skia2/docs/SkCanvas_Reference.bmh

#Topic Canvas
#Alias Canvas_Reference ##

#Class SkCanvas

#Code
#Populate
##

Canvas provides an interface for drawing, and how the drawing is clipped and transformed.
Canvas contains a stack of Matrix and Clip values.

Canvas and Paint together provide the state to draw into Surface or Device.
Each Canvas draw call transforms the geometry of the object by the concatenation of all
Matrix values in the stack. The transformed geometry is clipped by the intersection
of all of Clip values in the stack. The Canvas draw calls use Paint to supply drawing
state such as Color, Typeface, text size, stroke width, Shader and so on.

To draw to a pixel-based destination, create Raster_Surface or GPU_Surface.
Request Canvas from Surface to obtain the interface to draw.
Canvas generated by Raster_Surface draws to memory visible to the CPU.
Canvas generated by GPU_Surface uses Vulkan or OpenGL to draw to the GPU.

To draw to a document, obtain Canvas from SVG_Canvas, Document_PDF, or Picture_Recorder.
Document based Canvas and other Canvas subclasses reference Device describing the
destination.

Canvas can be constructed to draw to Bitmap without first creating Raster_Surface.
This approach may be deprecated in the future.

Canvas may be created directly when no Surface is required; some Canvas methods
implicitly create Raster_Surface.

# ------------------------------------------------------------------------------

#Method static std::unique_ptr<SkCanvas> MakeRasterDirect(const SkImageInfo& info, void* pixels,
                                                          size_t rowBytes,
                                                          const SkSurfaceProps* props = nullptr)
#In Constructors
#Line # creates from SkImageInfo and Pixel_Storage ##
#Populate

#Example
    #Description
        Allocates a three by three bitmap, clears it to white, and draws a black pixel
        in the center.
    ##
void draw(SkCanvas* ) {
    SkImageInfo info = SkImageInfo::MakeN32Premul(3, 3);  // device aligned, 32 bpp, Premultiplied
    const size_t minRowBytes = info.minRowBytes();  // bytes used by one bitmap row
    const size_t size = info.computeMinByteSize();  // bytes used by all rows
    SkAutoTMalloc<SkPMColor> storage(size);  // allocate storage for pixels
    SkPMColor* pixels = storage.get();  // get pointer to allocated storage
    // create a SkCanvas backed by a raster device, and delete it when the
    // function goes out of scope.
    std::unique_ptr<SkCanvas> canvas = SkCanvas::MakeRasterDirect(info, pixels, minRowBytes);
    canvas->clear(SK_ColorWHITE);  // white is Unpremultiplied, in ARGB order
    canvas->flush();  // ensure that pixels are cleared
    SkPMColor pmWhite = pixels[0];  // the Premultiplied format may vary
    SkPaint paint;  // by default, draws black
    canvas->drawPoint(1, 1, paint);  // draw in the center
    canvas->flush();  // ensure that point was drawn
    for (int y = 0; y < info.height(); ++y) {
        for (int x = 0; x < info.width(); ++x) {
            SkDebugf("%c", *pixels++ == pmWhite ? '-' : 'x');
        }
        SkDebugf("\n");
    }
}
    #StdOut
        ---
        -x-
        ---
    ##
##

#SeeAlso MakeRasterDirectN32 SkSurface::MakeRasterDirect

##

# ------------------------------------------------------------------------------

#Method static std::unique_ptr<SkCanvas> MakeRasterDirectN32(int width, int height, SkPMColor* pixels,
                                                         size_t rowBytes)
#In Constructors
#Line # creates from image data and Pixel_Storage ##
#Populate

#Example
    #Description
        Allocates a three by three bitmap, clears it to white, and draws a black pixel
        in the center.
    ##
void draw(SkCanvas* ) {
    const int width = 3;
    const int height = 3;
    SkPMColor pixels[height][width];  // allocate a 3 by 3 Premultiplied bitmap on the stack
    // create a SkCanvas backed by a raster device, and delete it when the
    // function goes out of scope.
    std::unique_ptr<SkCanvas> canvas = SkCanvas::MakeRasterDirectN32(
            width,
            height,
            pixels[0],  // top-left of the bitmap
            sizeof(pixels[0]));  // byte width of the each row
    // write a Premultiplied value for white into all pixels in the bitmap
    canvas->clear(SK_ColorWHITE);
    SkPMColor pmWhite = pixels[0][0];  // the Premultiplied format may vary
    SkPaint paint;  // by default, draws black
    canvas->drawPoint(1, 1, paint);  // draw in the center
    canvas->flush();  // ensure that pixels is ready to be read
    for (int y = 0; y < height; ++y) {
        for (int x = 0; x < width; ++x) {
            SkDebugf("%c", pixels[y][x] == pmWhite ? '-' : 'x');
        }
        SkDebugf("\n");
    }
}
    #StdOut
        ---
        -x-
        ---
    ##
##

#SeeAlso MakeRasterDirect SkSurface::MakeRasterDirect SkImageInfo::MakeN32Premul

##

# ------------------------------------------------------------------------------

#Method SkCanvas()

#Line # creates with no Surface, no dimensions ##
#Populate

#Example

#Description
Passes a placeholder to a function that requires one.
##

#Function
static void check_for_rotated_ctm(const SkCanvas* canvas) {
    const SkMatrix& matrix = canvas->getTotalMatrix();
    SkDebugf("rect stays rect is %s\n", matrix.rectStaysRect() ? "true" : "false");
}

##
void draw(SkCanvas* canvas) {
    check_for_rotated_ctm(canvas);
    canvas->rotate(30);
    check_for_rotated_ctm(canvas);

    SkCanvas defaultCanvas;
    check_for_rotated_ctm(&defaultCanvas);
}

    #StdOut
        rect stays rect is true
        rect stays rect is false
        rect stays rect is true
    ##
##

#SeeAlso MakeRasterDirect SkRasterHandleAllocator::MakeCanvas SkSurface::getCanvas SkCreateColorSpaceXformCanvas

##

# ------------------------------------------------------------------------------

#Method SkCanvas(int width, int height, const SkSurfaceProps* props = nullptr)

#Line # creates with no Surface, set dimensions, Surface_Properties ##
#Populate

#Example
    SkCanvas canvas(10, 20);  // 10 units wide, 20 units high
    canvas.clipRect(SkRect::MakeXYWH(30, 40, 5, 10));  // clip is outside canvas' device
    SkDebugf("canvas %s empty\n", canvas.getDeviceClipBounds().isEmpty() ? "is" : "is not");

    #StdOut
        canvas is empty
    ##
##

#SeeAlso MakeRasterDirect SkSurfaceProps SkPixelGeometry SkCreateColorSpaceXformCanvas

##

# ------------------------------------------------------------------------------

#Method explicit SkCanvas(const SkBitmap& bitmap)

#Line # uses existing Bitmap ##
#Populate

#Example
#Description
The actual output depends on the installed fonts.
##
    SkBitmap bitmap;
    // create a bitmap 5 wide and 11 high
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(5, 11));
    SkCanvas canvas(bitmap);
    canvas.clear(SK_ColorWHITE);  // white is Unpremultiplied, in ARGB order
    SkPixmap pixmap;  // provides guaranteed access to the drawn pixels
    if (!canvas.peekPixels(&pixmap)) {
        SkDebugf("peekPixels should never fail.\n");
    }
    const SkPMColor* pixels = pixmap.addr32();  // points to top-left of bitmap
    SkPMColor pmWhite = pixels[0];  // the Premultiplied format may vary
    SkPaint paint;  // by default, draws black, 12 point text
    canvas.drawString("!", 1, 10, SkFont(), paint);  // 1 char at baseline (1, 10)
    for (int y = 0; y < bitmap.height(); ++y) {
        for (int x = 0; x < bitmap.width(); ++x) {
            SkDebugf("%c", *pixels++ == pmWhite ? '-' : 'x');
        }
        SkDebugf("\n");
    }

    #StdOut
    -----
    ---x-
    ---x-
    ---x-
    ---x-
    ---x-
    ---x-
    -----
    ---x-
    ---x-
    -----
    #StdOut ##
##

#SeeAlso MakeRasterDirect SkRasterHandleAllocator::MakeCanvas SkSurface::getCanvas SkCreateColorSpaceXformCanvas

##

# ------------------------------------------------------------------------------

#Method SkCanvas(const SkBitmap& bitmap, const SkSurfaceProps& props)

#Line # uses existing Bitmap and Surface_Properties ##
#Populate

#Example
#Description
The actual output depends on the installed fonts.
##
    SkBitmap bitmap;
    // create a bitmap 5 wide and 11 high
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(5, 11));
    SkCanvas canvas(bitmap, SkSurfaceProps(0, kUnknown_SkPixelGeometry));
    canvas.clear(SK_ColorWHITE);  // white is Unpremultiplied, in ARGB order
    SkPixmap pixmap;  // provides guaranteed access to the drawn pixels
    if (!canvas.peekPixels(&pixmap)) {
        SkDebugf("peekPixels should never fail.\n");
    }
    const SkPMColor* pixels = pixmap.addr32();  // points to top-left of bitmap
    SkPMColor pmWhite = pixels[0];  // the Premultiplied format may vary
    SkPaint paint;  // by default, draws black, 12 point text
    canvas.drawString("!", 1, 10, SkFont(), paint);  // 1 char at baseline (1, 10)
    for (int y = 0; y < bitmap.height(); ++y) {
        for (int x = 0; x < bitmap.width(); ++x) {
            SkDebugf("%c", *pixels++ == pmWhite ? '-' : 'x');
        }
        SkDebugf("\n");
    }

    #StdOut
    -----
    ---x-
    ---x-
    ---x-
    ---x-
    ---x-
    ---x-
    -----
    ---x-
    ---x-
    -----
    #StdOut ##
##

#SeeAlso MakeRasterDirect SkRasterHandleAllocator::MakeCanvas SkSurface::getCanvas SkCreateColorSpaceXformCanvas

##

# ------------------------------------------------------------------------------

#Method virtual ~SkCanvas()

#Line # draws saved Layers, frees resources ##
#Populate

#Example
#Description
Canvas Layer draws into bitmap. saveLayerAlpha sets up an additional
drawing surface that blends with the bitmap. When Layer goes out of
scope, Layer destructor is called. The saved Layer is restored, drawing
transparent letters.
##
void draw(SkCanvas* canvas) {
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(200, 200));
    {
        SkCanvas offscreen(bitmap);
        SkPaint paint;
        SkFont font(nullptr, 100);
        offscreen.drawString("ABC", 20, 160, font, paint);
        SkRect layerBounds = SkRect::MakeXYWH(32, 32, 192, 192);
        offscreen.saveLayerAlpha(&layerBounds, 128);
        offscreen.clear(SK_ColorWHITE);
        offscreen.drawString("DEF", 20, 160, font, paint);
    }
    canvas->drawBitmap(bitmap, 0, 0, nullptr);
}
##

#SeeAlso State_Stack

##

# ------------------------------------------------------------------------------
#Subtopic Property
#Line # metrics and attributes ##
##

#Method SkImageInfo imageInfo() const
#In Property
#Line # returns Image_Info for Canvas ##
#Populate

#Example
    SkCanvas emptyCanvas;
    SkImageInfo canvasInfo = emptyCanvas.imageInfo();
    SkImageInfo emptyInfo;
    SkDebugf("emptyInfo %c= canvasInfo\n", emptyInfo == canvasInfo ? '=' : '!');

    #StdOut
        emptyInfo == canvasInfo
    ##
##

#SeeAlso SkImageInfo MakeRasterDirect makeSurface

##

# ------------------------------------------------------------------------------

#Method bool getProps(SkSurfaceProps* props) const
#In Property
#Line # copies Surface_Properties if available ##
#Populate

#Example
    SkBitmap bitmap;
    SkCanvas canvas(bitmap, SkSurfaceProps(0, kRGB_V_SkPixelGeometry));
    SkSurfaceProps surfaceProps(0, kUnknown_SkPixelGeometry);
    SkDebugf("isRGB:%d\n", SkPixelGeometryIsRGB(surfaceProps.pixelGeometry()));
    if (!canvas.getProps(&surfaceProps)) {
        SkDebugf("getProps failed unexpectedly.\n");
    }
    SkDebugf("isRGB:%d\n", SkPixelGeometryIsRGB(surfaceProps.pixelGeometry()));

    #StdOut
        isRGB:0
        isRGB:1
    #StdOut ##
##

#SeeAlso SkSurfaceProps makeSurface

##

# ------------------------------------------------------------------------------
#Subtopic Utility
#Line # rarely called management functions ##
##

#Method void flush()
#In Utility
#Line # triggers execution of all pending draw operations ##
#Populate

#NoExample
##

#SeeAlso peekPixels SkSurface::flush GrContext::flush GrContext::abandonContext

##

# ------------------------------------------------------------------------------

#Method virtual SkISize getBaseLayerSize() const
#In Property
#Line # returns size of base Layer in global coordinates ##
#Populate

#Example
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(20, 30));
    SkCanvas canvas(bitmap, SkSurfaceProps(0, kUnknown_SkPixelGeometry));
    canvas.clipRect(SkRect::MakeWH(10, 40));
    SkIRect clipDeviceBounds = canvas.getDeviceClipBounds();
    if (clipDeviceBounds.isEmpty()) {
        SkDebugf("Empty clip bounds is unexpected!\n");
    }
    SkDebugf("clip=%d,%d\n", clipDeviceBounds.width(), clipDeviceBounds.height());
    SkISize baseLayerSize = canvas.getBaseLayerSize();
    SkDebugf("size=%d,%d\n", baseLayerSize.width(), baseLayerSize.height());

    #StdOut
        clip=10,30
        size=20,30
    ##
##

#ToDo is this the same as the width and height of surface? ##

#SeeAlso getDeviceClipBounds

##

# ------------------------------------------------------------------------------

#Method sk_sp<SkSurface> makeSurface(const SkImageInfo& info, const SkSurfaceProps* props = nullptr)
#In Constructors
#Line # creates Surface matching SkImageInfo and SkSurfaceProps ##
#Populate

#Example
    sk_sp<SkSurface> surface = SkSurface::MakeRasterN32Premul(5, 6);
    SkCanvas* smallCanvas = surface->getCanvas();
    SkImageInfo imageInfo = SkImageInfo::MakeN32Premul(3, 4);
    sk_sp<SkSurface> compatible = smallCanvas->makeSurface(imageInfo);
    SkDebugf("compatible %c= nullptr\n", compatible == nullptr ? '=' : '!');
    SkDebugf("size = %d, %d\n", compatible->width(), compatible->height());

    #StdOut
        compatible != nullptr
        size = 3, 4
    ##
##

#SeeAlso SkSurface SkSurface::makeSurface SkImageInfo SkSurfaceProps

##

# ------------------------------------------------------------------------------

#Method virtual GrContext* getGrContext()
#In Property
#Line # returns GPU_Context of the GPU_Surface ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    if (canvas->getGrContext()) {
         canvas->clear(SK_ColorRED);
    } else {
         canvas->clear(SK_ColorBLUE);
    }
}
##

#ToDo fiddle should show both CPU and GPU out ##

#SeeAlso GrContext

##

# ------------------------------------------------------------------------------

#Method void* accessTopLayerPixels(SkImageInfo* info, size_t* rowBytes, SkIPoint* origin = nullptr)
#In Utility
#In Property
#Line # returns writable pixel access if available ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    if (canvas->accessTopLayerPixels(nullptr, nullptr)) {
         canvas->clear(SK_ColorRED);
    } else {
         canvas->clear(SK_ColorBLUE);
    }
}
##

#Example
#Description
Draws "ABC" on the device. Then draws "DEF" in Layer, and reads
Layer to add a large dotted "DEF". Finally blends Layer with the
device.

The Layer and blended result appear on the CPU and GPU but the large dotted
"DEF" appear only on the CPU.
##
void draw(SkCanvas* canvas) {
  SkPaint paint;
  SkFont font(nullptr, 100);
  canvas->drawString("ABC", 20, 160, font, paint);
  SkRect layerBounds = SkRect::MakeXYWH(32, 32, 192, 192);
  canvas->saveLayerAlpha(&layerBounds, 128);
  canvas->clear(SK_ColorWHITE);
  canvas->drawString("DEF", 20, 160, font, paint);
  SkImageInfo imageInfo;
  size_t rowBytes;
  SkIPoint origin;
  uint32_t* access = (uint32_t*) canvas->accessTopLayerPixels(&imageInfo, &rowBytes, &origin);
  if (access) {
    int h = imageInfo.height();
    int v = imageInfo.width();
    int rowWords = rowBytes / sizeof(uint32_t);
    for (int y = 0; y < h; ++y) {
        int newY = (y - h / 2) * 2 + h / 2;
        if (newY < 0 || newY >= h) {
            continue;
        }
        for (int x = 0; x < v; ++x) {
            int newX = (x - v / 2) * 2 + v / 2;
            if (newX < 0 || newX >= v) {
                continue;
            }
            if (access[y * rowWords + x] == SK_ColorBLACK) {
                access[newY * rowWords + newX] = SK_ColorGRAY;
            }
        }
    }

  }
  canvas->restore();
}
##

#ToDo there are no callers of this that I can find. Deprecate? ##
#ToDo fiddle should show both CPU and GPU out ##

#SeeAlso SkImageInfo SkPixmap

##

# ------------------------------------------------------------------------------

#Method SkRasterHandleAllocator::Handle accessTopRasterHandle() const
#In Utility
#In Property
#Line # returns context that tracks Clip and Matrix ##
#Populate

#Example
#Description
#ToDo ##
##
#Function
    static void DeleteCallback(void*, void* context) {
        delete (char*) context;
    }

    class CustomAllocator : public SkRasterHandleAllocator {
    public:
        bool allocHandle(const SkImageInfo& info, Rec* rec) override {
            char* context = new char[4]{'s', 'k', 'i', 'a'};
            rec->fReleaseProc = DeleteCallback;
            rec->fReleaseCtx = context;
            rec->fHandle = context;
            rec->fPixels = context;
            rec->fRowBytes = 4;
            return true;
        }

        void updateHandle(Handle handle, const SkMatrix& ctm, const SkIRect& clip_bounds) override {
            // apply canvas matrix and clip to custom environment
        }
    };

##
    void draw(SkCanvas* canvas) {
        const SkImageInfo info = SkImageInfo::MakeN32Premul(1, 1);
        std::unique_ptr<SkCanvas> c2 =
                SkRasterHandleAllocator::MakeCanvas(std::unique_ptr<CustomAllocator>(
                new CustomAllocator()), info);
        char* context = (char*) c2->accessTopRasterHandle();
        SkDebugf("context = %.4s\n", context);

    }
    #StdOut
        context = skia
    ##
    #ToDo skstd::make_unique could not be used because def is private -- note to fix in c++14? ##
##

#SeeAlso SkRasterHandleAllocator

##

# ------------------------------------------------------------------------------
#Subtopic Pixels
#Line # read and write pixel values ##
##

#Method bool peekPixels(SkPixmap* pixmap)
#In Pixels
#Line # returns if Canvas has direct access to its pixels ##
#Populate

#Example
    SkPixmap pixmap;
    if (canvas->peekPixels(&pixmap)) {
        SkDebugf("width=%d height=%d\n", pixmap.bounds().width(), pixmap.bounds().height());
    }
    #StdOut
        width=256 height=256
    ##
##

#SeeAlso readPixels SkBitmap::peekPixels SkImage::peekPixels SkSurface::peekPixels

##

# ------------------------------------------------------------------------------

#Method bool readPixels(const SkImageInfo& dstInfo, void* dstPixels, size_t dstRowBytes,
                    int srcX, int srcY)
#In Pixels
#Line # copies and converts rectangle of pixels from Canvas ##

Copies Rect of pixels from Canvas into dstPixels. Matrix and Clip are
ignored.

Source Rect corners are (srcX, srcY) and (imageInfo().width(), imageInfo().height()).
Destination Rect corners are (0, 0) and (dstInfo.width(), dstInfo.height()).
Copies each readable pixel intersecting both rectangles, without scaling,
converting to dstInfo.colorType() and dstInfo.alphaType() if required.

Pixels are readable when Device is raster, or backed by a GPU.
Pixels are not readable when SkCanvas is returned by SkDocument::beginPage,
returned by SkPictureRecorder::beginRecording, or Canvas is the base of a utility
class like SkDebugCanvas.

The destination pixel storage must be allocated by the caller.

Pixel values are converted only if Color_Type and Alpha_Type
do not match. Only pixels within both source and destination rectangles
are copied. dstPixels contents outside Rect intersection are unchanged.

Pass negative values for srcX or srcY to offset pixels across or down destination.

Does not copy, and returns false if:

#List
# Source and destination rectangles do not intersect. ##
# Canvas pixels could not be converted to dstInfo.colorType() or dstInfo.alphaType(). ##
# Canvas pixels are not readable; for instance, Canvas is document-based. ##
# dstRowBytes is too small to contain one row of pixels. ##
##

#Param dstInfo  width, height, Color_Type, and Alpha_Type of dstPixels ##
#Param dstPixels  storage for pixels; dstInfo.height() times dstRowBytes, or larger ##
#Param dstRowBytes  size of one destination row; dstInfo.width() times pixel size, or larger ##
#Param srcX  offset into readable pixels on x-axis; may be negative ##
#Param srcY  offset into readable pixels on y-axis; may be negative ##

#Return  true if pixels were copied ##

#Example
#Width 64
#Height 64
#Description
    A black circle drawn on a blue background provides an image to copy.
    readPixels copies one quarter of the canvas into each of the four corners.
    The copied quarter circles overdraw the original circle.
##
    canvas->clear(SK_ColorBLUE);
    SkPaint paint;
    canvas->drawCircle(32, 32, 28, paint);
    SkImageInfo info = SkImageInfo::Make(64, 64, kBGRA_8888_SkColorType, kPremul_SkAlphaType);
    sk_sp<SkData> data(SkData::MakeUninitialized(info.minRowBytes() * info.height()));
    sk_bzero(data->writable_data(), info.minRowBytes() * info.height());
    for (int x : { 32, -32 } ) {
        for (int y : { 32, -32 } ) {
            canvas->readPixels(info, data->writable_data(), info.minRowBytes(), x, y);
        }
    }
    sk_sp<SkImage> image = SkImage::MakeRasterData(info, data, info.minRowBytes());
    canvas->drawImage(image, 0, 0);
##

#Example
#Description
    Canvas returned by Raster_Surface has Premultiplied pixel values.
    clear() takes Unpremultiplied input with Color_Alpha equal 0x80
    and RGB equal 0x55, 0xAA, 0xFF. RGB is multiplied by Color_Alpha
    to generate Premultiplied value 0x802B5580. readPixels converts pixel back
    to Unpremultiplied value 0x8056A9FF, introducing error.
##
    canvas->clear(0x8055aaff);
    for (SkAlphaType alphaType : { kPremul_SkAlphaType, kUnpremul_SkAlphaType } ) {
        uint32_t pixel = 0;
        SkImageInfo info = SkImageInfo::Make(1, 1, kBGRA_8888_SkColorType, alphaType);
        if (canvas->readPixels(info, &pixel, 4, 0, 0)) {
            SkDebugf("pixel = %08x\n", pixel);
        }
    }

    #StdOut
        pixel = 802b5580
        pixel = 8056a9ff
    ##
##

#SeeAlso peekPixels writePixels drawBitmap drawImage SkBitmap::readPixels SkPixmap::readPixels SkImage::readPixels SkSurface::readPixels

##

# ------------------------------------------------------------------------------

#Method bool readPixels(const SkPixmap& pixmap, int srcX, int srcY)

Copies Rect of pixels from Canvas into pixmap. Matrix and Clip are
ignored.

Source Rect corners are (srcX, srcY) and (imageInfo().width(), imageInfo().height()).
Destination Rect corners are (0, 0) and (pixmap.width(), pixmap.height()).
Copies each readable pixel intersecting both rectangles, without scaling,
converting to pixmap.colorType() and pixmap.alphaType() if required.

Pixels are readable when Device is raster, or backed by a GPU.
Pixels are not readable when SkCanvas is returned by SkDocument::beginPage,
returned by SkPictureRecorder::beginRecording, or Canvas is the base of a utility
class like SkDebugCanvas.

Caller must allocate pixel storage in pixmap if needed.

Pixel values are converted only if Color_Type and Alpha_Type
do not match. Only pixels within both source and destination Rects
are copied. pixmap pixels contents outside Rect intersection are unchanged.

Pass negative values for srcX or srcY to offset pixels across or down pixmap.

Does not copy, and returns false if:

#List
# Source and destination rectangles do not intersect. ##
# Canvas pixels could not be converted to pixmap.colorType() or pixmap.alphaType(). ##
# Canvas pixels are not readable; for instance, Canvas is document-based. ##
# Pixmap pixels could not be allocated. ##
# pixmap.rowBytes() is too small to contain one row of pixels. ##
##

#Param pixmap  storage for pixels copied from Canvas ##
#Param srcX    offset into readable pixels on x-axis; may be negative ##
#Param srcY    offset into readable pixels on y-axis; may be negative ##

#Return  true if pixels were copied ##

#Example
    #Description
        clear() takes Unpremultiplied input with Color_Alpha equal 0x80
        and RGB equal 0x55, 0xAA, 0xFF. RGB is multiplied by Color_Alpha
        to generate Premultiplied value 0x802B5580.
    ##
    void draw(SkCanvas* canvas) {
        canvas->clear(0x8055aaff);
        uint32_t pixels[1] = { 0 };
        SkPixmap pixmap(SkImageInfo::MakeN32Premul(1, 1), pixels, 4);
        canvas->readPixels(pixmap, 0, 0);
        SkDebugf("pixel = %08x\n", pixels[0]);
    }
    #StdOut
        pixel = 802b5580
    ##
##

#SeeAlso peekPixels writePixels drawBitmap drawImage SkBitmap::readPixels SkPixmap::readPixels SkImage::readPixels SkSurface::readPixels

##

# ------------------------------------------------------------------------------

#Method bool readPixels(const SkBitmap& bitmap, int srcX, int srcY)

Copies Rect of pixels from Canvas into bitmap. Matrix and Clip are
ignored.

Source Rect corners are (srcX, srcY) and (imageInfo().width(), imageInfo().height()).
Destination Rect corners are (0, 0) and (bitmap.width(), bitmap.height()).
Copies each readable pixel intersecting both rectangles, without scaling,
converting to bitmap.colorType() and bitmap.alphaType() if required.

Pixels are readable when Device is raster, or backed by a GPU.
Pixels are not readable when SkCanvas is returned by SkDocument::beginPage,
returned by SkPictureRecorder::beginRecording, or Canvas is the base of a utility
class like SkDebugCanvas.

Caller must allocate pixel storage in bitmap if needed.

Bitmap values are converted only if Color_Type and Alpha_Type
do not match. Only pixels within both source and destination rectangles
are copied. Bitmap pixels outside Rect intersection are unchanged.

Pass negative values for srcX or srcY to offset pixels across or down bitmap.

Does not copy, and returns false if:

#List
# Source and destination rectangles do not intersect. ##
# Canvas pixels could not be converted to bitmap.colorType() or bitmap.alphaType(). ##
# Canvas pixels are not readable; for instance, Canvas is document-based. ##
# bitmap pixels could not be allocated. ##
# bitmap.rowBytes() is too small to contain one row of pixels. ##
##

#Param bitmap  storage for pixels copied from Canvas ##
#Param srcX    offset into readable pixels on x-axis; may be negative ##
#Param srcY    offset into readable pixels on y-axis; may be negative ##

#Return  true if pixels were copied ##

#Example
    #Description
        clear() takes Unpremultiplied input with Color_Alpha equal 0x80
        and RGB equal 0x55, 0xAA, 0xFF. RGB is multiplied by Color_Alpha
        to generate Premultiplied value 0x802B5580.
    ##
void draw(SkCanvas* canvas) {
    canvas->clear(0x8055aaff);
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(1, 1));
    canvas->readPixels(bitmap, 0, 0);
    SkDebugf("pixel = %08x\n", bitmap.getAddr32(0, 0)[0]);
}
    #StdOut
        pixel = 802b5580
    ##
##

#SeeAlso peekPixels writePixels drawBitmap drawImage SkBitmap::readPixels SkPixmap::readPixels SkImage::readPixels SkSurface::readPixels

##

# ------------------------------------------------------------------------------

#Method bool writePixels(const SkImageInfo& info, const void* pixels, size_t rowBytes, int x, int y)
#In Pixels
#Line # copies and converts rectangle of pixels to Canvas ##
Copies Rect from pixels to Canvas. Matrix and Clip are ignored.
Source Rect corners are (0, 0) and (info.width(), info.height()).
Destination Rect corners are (x, y) and
(imageInfo().width(), imageInfo().height()).

Copies each readable pixel intersecting both rectangles, without scaling,
converting to imageInfo().colorType() and imageInfo().alphaType() if required.

Pixels are writable when Device is raster, or backed by a GPU.
Pixels are not writable when SkCanvas is returned by SkDocument::beginPage,
returned by SkPictureRecorder::beginRecording, or Canvas is the base of a utility
class like SkDebugCanvas.

Pixel values are converted only if Color_Type and Alpha_Type
do not match. Only pixels within both source and destination rectangles
are copied. Canvas pixels outside Rect intersection are unchanged.

Pass negative values for x or y to offset pixels to the left or
above Canvas pixels.

Does not copy, and returns false if:

#List
# Source and destination rectangles do not intersect. ##
# pixels could not be converted to Canvas imageInfo().colorType() or
  imageInfo().alphaType(). ##
# Canvas pixels are not writable; for instance, Canvas is document-based. ##
# rowBytes is too small to contain one row of pixels. ##
##

#Param info  width, height, Color_Type, and Alpha_Type of pixels ##
#Param pixels  pixels to copy, of size info.height() times rowBytes, or larger ##
#Param rowBytes  size of one row of pixels; info.width() times pixel size, or larger ##
#Param x  offset into Canvas writable pixels on x-axis; may be negative ##
#Param y  offset into Canvas writable pixels on y-axis; may be negative ##

#Return  true if pixels were written to Canvas ##

#Example
    SkImageInfo imageInfo = SkImageInfo::MakeN32(256, 1, kPremul_SkAlphaType);
    for (int y = 0; y < 256; ++y) {
        uint32_t pixels[256];
        for (int x = 0; x < 256; ++x) {
            pixels[x] = SkColorSetARGB(x, x + y, x, x - y);
        }
        canvas->writePixels(imageInfo, &pixels, sizeof(pixels), 0, y);
    }
##

#SeeAlso readPixels drawBitmap drawImage SkBitmap::writePixels

##

# ------------------------------------------------------------------------------

#Method bool writePixels(const SkBitmap& bitmap, int x, int y)

Copies Rect from pixels to Canvas. Matrix and Clip are ignored.
Source Rect corners are (0, 0) and (bitmap.width(), bitmap.height()).

Destination Rect corners are (x, y) and
(imageInfo().width(), imageInfo().height()).

Copies each readable pixel intersecting both rectangles, without scaling,
converting to imageInfo().colorType() and imageInfo().alphaType() if required.

Pixels are writable when Device is raster, or backed by a GPU.
Pixels are not writable when SkCanvas is returned by SkDocument::beginPage,
returned by SkPictureRecorder::beginRecording, or Canvas is the base of a utility
class like SkDebugCanvas.

Pixel values are converted only if Color_Type and Alpha_Type
do not match. Only pixels within both source and destination rectangles
are copied. Canvas pixels outside Rect intersection are unchanged.

Pass negative values for x or y to offset pixels to the left or
above Canvas pixels.

Does not copy, and returns false if:

#List
# Source and destination rectangles do not intersect. ##
# bitmap does not have allocated pixels. ##
# bitmap pixels could not be converted to Canvas imageInfo().colorType() or
  imageInfo().alphaType(). ##
# Canvas pixels are not writable; for instance, Canvas is document based. ##
# bitmap pixels are inaccessible; for instance, bitmap wraps a texture. ##
##

#Param bitmap  contains pixels copied to Canvas ##
#Param x       offset into Canvas writable pixels in x; may be negative ##
#Param y       offset into Canvas writable pixels in y; may be negative ##

#Return  true if pixels were written to Canvas ##

#Example
void draw(SkCanvas* canvas) {
    SkImageInfo imageInfo = SkImageInfo::MakeN32Premul(2, 2);
    SkBitmap bitmap;
    bitmap.setInfo(imageInfo);
    uint32_t pixels[4];
    bitmap.setPixels(pixels);
    for (int y = 0; y < 256; y += 2) {
        for (int x = 0; x < 256;  x += 2) {
            pixels[0] = SkColorSetRGB(x, y, x | y);
            pixels[1] = SkColorSetRGB(x ^ y, y, x);
            pixels[2] = SkColorSetRGB(x, x & y, y);
            pixels[3] = SkColorSetRGB(~x, ~y, x);
            canvas->writePixels(bitmap, x, y);
        }
    }
}
##

#SeeAlso readPixels drawBitmap drawImage SkBitmap::writePixels

##

# ------------------------------------------------------------------------------
#Subtopic State_Stack
#Line # stack of state for hierarchical drawing ##

Canvas maintains a stack of state that allows hierarchical drawing, commonly used
to implement windows and views. The initial state has an identity matrix and and
an infinite clip. Even with a wide-open clip, drawing is constrained by the
bounds of the Canvas Surface or Device.

Canvas savable state consists of Clip and Matrix.
Clip describes the area that may be drawn to.
Matrix transforms the geometry.

save(), saveLayer, and saveLayerAlpha
save state and return the depth of the stack.

restore(), restoreToCount, and ~SkCanvas() revert state to its value when saved.

Each state on the stack intersects Clip with the previous Clip,
and concatenates Matrix with the previous Matrix.
The intersected Clip makes the drawing area the same or smaller;
the concatenated Matrix may move the origin and potentially scale or rotate
the coordinate space.

Canvas does not require balancing the state stack but it is a good idea
to do so. Calling save() without restore() will eventually cause Skia to fail;
mismatched save() and restore() create hard to find bugs.

It is not possible to use state to draw outside of the clip defined by the
previous state.

#Example
#Description
Draw to ever smaller clips; then restore drawing to full canvas.
Note that the second clipRect is not permitted to enlarge Clip.
##
#Height 160
void draw(SkCanvas* canvas) {
    SkPaint paint;
    canvas->save();                             // records stack depth to restore
    canvas->clipRect(SkRect::MakeWH(100, 100)); // constrains drawing to clip
    canvas->clear(SK_ColorRED);                 // draws to limit of clip
    canvas->save();                             // records stack depth to restore
    canvas->clipRect(SkRect::MakeWH(50, 150));  // Rect below 100 is ignored
    canvas->clear(SK_ColorBLUE);                // draws to smaller clip
    canvas->restore();                          // enlarges clip
    canvas->drawLine(20, 20, 150, 150, paint);  // line below 100 is not drawn
    canvas->restore();                          // enlarges clip
    canvas->drawLine(150, 20, 50, 120, paint);  // line below 100 is drawn
}
##

Each Clip uses the current Matrix for its coordinates.

#Example
#Description
While clipRect is given the same rectangle twice, Matrix makes the second
clipRect draw at half the size of the first.
##
#Height 128
void draw(SkCanvas* canvas) {
    canvas->clipRect(SkRect::MakeWH(100, 100));
    canvas->clear(SK_ColorRED);
    canvas->scale(.5, .5);
    canvas->clipRect(SkRect::MakeWH(100, 100));
    canvas->clear(SK_ColorBLUE);
}
##

#SeeAlso save saveLayer saveLayerAlpha restore() restoreToCount

#Method int save()

#In State_Stack
#Line # saves Clip and Matrix on stack ##
#Populate

#Example
#Description
The black square is translated 50 pixels down and to the right.
Restoring Canvas state removes translate() from Canvas stack;
the red square is not translated, and is drawn at the origin.
##
#Height 100
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkRect rect = { 0, 0, 25, 25 };
    canvas->drawRect(rect, paint);
    canvas->save();
    canvas->translate(50, 50);
    canvas->drawRect(rect, paint);
    canvas->restore();
    paint.setColor(SK_ColorRED);
    canvas->drawRect(rect, paint);
}
##

#SeeAlso saveLayer saveLayerAlpha restore restoreToCount

##

# ------------------------------------------------------------------------------

#Method void restore()

#In State_Stack
#Line # restores changes to Clip and Matrix, pops save stack ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkCanvas simple;
    SkDebugf("depth = %d\n", simple.getSaveCount());
    simple.restore();
    SkDebugf("depth = %d\n", simple.getSaveCount());
}
##

#SeeAlso save saveLayer saveLayerAlpha restoreToCount

##

# ------------------------------------------------------------------------------

#Method int getSaveCount() const

#In State_Stack
#Line # returns depth of stack containing Clip and Matrix ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkCanvas simple;
    SkDebugf("depth = %d\n", simple.getSaveCount());
    simple.save();
    SkDebugf("depth = %d\n", simple.getSaveCount());
    simple.restore();
    SkDebugf("depth = %d\n", simple.getSaveCount());
}
#StdOut
depth = 1
depth = 2
depth = 1
##
##

#SeeAlso save restore restoreToCount

##

# ------------------------------------------------------------------------------

#Method void restoreToCount(int saveCount)

#In State_Stack
#Line # restores changes to Clip and Matrix to given depth ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkDebugf("depth = %d\n", canvas->getSaveCount());
    canvas->save();
    canvas->save();
    SkDebugf("depth = %d\n", canvas->getSaveCount());
    canvas->restoreToCount(0);
    SkDebugf("depth = %d\n", canvas->getSaveCount());
}
#StdOut
depth = 1
depth = 3
depth = 1
##
##

#SeeAlso restore getSaveCount save

##

#Subtopic State_Stack ##

# ------------------------------------------------------------------------------

#Subtopic Layer
#Substitute layer
#Alias Layers
#Substitute layers
##
#Line # temporary Bitmap to draw into ##

Layer allocates a temporary Bitmap to draw into. When the drawing is
complete, the Bitmap is drawn into the Canvas.

Layer is saved in a stack along with other saved state. When state with a Layer
is restored, the Bitmap is drawn into the previous Layer.

Layer may be initialized with the contents of the previous Layer. When Layer is
restored, its Bitmap can be modified by Paint passed to Layer to apply
Color_Alpha, Color_Filter, Image_Filter, and Blend_Mode.

#Method int saveLayer(const SkRect* bounds, const SkPaint* paint)

#In Layer
#Line # saves Clip and Matrix on stack; creates Layer ##
#Populate

#Example
#Description
Rectangles are blurred by Image_Filter when restore() draws Layer to main
Canvas.
##
#Height 128
#Function
###$
#include "SkBlurImageFilter.h"
$$$#
##

void draw(SkCanvas* canvas) {
    SkPaint paint, blur;
    blur.setImageFilter(SkBlurImageFilter::Make(3, 3, nullptr));
    canvas->saveLayer(nullptr, &blur);
    SkRect rect = { 25, 25, 50, 50};
    canvas->drawRect(rect, paint);
    canvas->translate(50, 50);
    paint.setColor(SK_ColorRED);
    canvas->drawRect(rect, paint);
    canvas->restore();
}
##

#SeeAlso save restore saveLayer saveLayerAlpha SaveLayerRec

##

#Method int saveLayer(const SkRect& bounds, const SkPaint* paint)

#In Layer
#Populate

#Example
#Description
Rectangles are blurred by Image_Filter when restore() draws Layer to main Canvas.
The red rectangle is clipped; it does not fully fit on Layer.
Image_Filter blurs past edge of Layer so red rectangle is blurred on all sides.
##
#Height 128
#Function
###$
#include "SkBlurImageFilter.h"
$$$#
##

void draw(SkCanvas* canvas) {
    SkPaint paint, blur;
    blur.setImageFilter(SkBlurImageFilter::Make(3, 3, nullptr));
    canvas->saveLayer(SkRect::MakeWH(90, 90), &blur);
    SkRect rect = { 25, 25, 50, 50};
    canvas->drawRect(rect, paint);
    canvas->translate(50, 50);
    paint.setColor(SK_ColorRED);
    canvas->drawRect(rect, paint);
    canvas->restore();
}
##

#SeeAlso save restore saveLayerAlpha SaveLayerRec

##

#Method int saveLayerAlpha(const SkRect* bounds, U8CPU alpha)

#In Layer
#Line # saves Clip and Matrix on stack; creates Layer; sets opacity ##
#Populate

#Example
    SkPaint paint;
    paint.setColor(SK_ColorRED);
    canvas->drawCircle(50, 50, 50, paint);
    canvas->saveLayerAlpha(nullptr, 128);
    paint.setColor(SK_ColorBLUE);
    canvas->drawCircle(100, 50, 50, paint);
    paint.setColor(SK_ColorGREEN);
    paint.setAlpha(128);
    canvas->drawCircle(75, 90, 50, paint);
    canvas->restore();
##

#SeeAlso save restore saveLayer SaveLayerRec

##

#Enum SaveLayerFlagsSet
#Line # sets SaveLayerRec options ##
#Code
#Populate
##


#Typedef uint32_t SaveLayerFlags
#Line # options for SaveLayerRec ##
##

SaveLayerFlags provides options that may be used in any combination in SaveLayerRec,
defining how Layer allocated by saveLayer operates. It may be set to zero or
kInitWithPrevious_SaveLayerFlag.

#Const kInitWithPrevious_SaveLayerFlag 4
#Line # initializes with previous contents ##
  Initializes Layer with the contents of the previous Layer.
##

#Example
#Height 160
#Description
Canvas Layer captures red and blue circles scaled up by four.
scalePaint blends Layer back with transparency.
##
void draw(SkCanvas* canvas) {
    SkPaint redPaint, bluePaint, scalePaint;
    redPaint.setColor(SK_ColorRED);
    canvas->drawCircle(21, 21, 8, redPaint);
    bluePaint.setColor(SK_ColorBLUE);
    canvas->drawCircle(31, 21, 8, bluePaint);
    SkMatrix matrix;
    matrix.setScale(4, 4);
    scalePaint.setAlpha(0x40);
    scalePaint.setImageFilter(
            SkImageFilter::MakeMatrixFilter(matrix, kNone_SkFilterQuality, nullptr));
    SkCanvas::SaveLayerRec saveLayerRec(nullptr, &scalePaint,
            SkCanvas::kInitWithPrevious_SaveLayerFlag);
    canvas->saveLayer(saveLayerRec);
    canvas->restore();
}
##

#SeeAlso save restore saveLayer saveLayerAlpha SaveLayerRec

#Enum ##

#Subtopic SaveLayerRec
#Line # contains the state used to create the Layer ##

#Struct SaveLayerRec
#Line # contains the state used to create the Layer ##

#Code
#Populate
##

SaveLayerRec contains the state used to create the Layer.

#Member const SkRect*           fBounds
#Line # hints at Layer size limit ##
    fBounds is used as a hint to limit the size of Layer; may be nullptr.
    fBounds suggests but does not define Layer size. To clip drawing to
    a specific rectangle, use clipRect.
##

#Member const SkPaint*          fPaint
#Line # modifies overlay ##
    fPaint modifies how Layer overlays the prior Layer; may be nullptr.
    Color_Alpha, Blend_Mode, Color_Filter, Draw_Looper, Image_Filter, and
    Mask_Filter affect Layer draw.
##

#Member const SkImageFilter*    fBackdrop
#Line # applies Image_Filter to prior Layer ##
    fBackdrop applies Image_Filter to the prior Layer when copying to the Layer;
    may be nullptr. Use kInitWithPrevious_SaveLayerFlag to copy the
    prior Layer without an Image_Filter.
##

#Member const SkImage*          fClipMask
#Line # clips Layer with Mask_Alpha ##
  restore() clips Layer by the Color_Alpha channel of fClipMask when
  Layer is copied to Device. fClipMask may be nullptr.    .
##

#Member const SkMatrix*         fClipMatrix
#Line # transforms Mask_Alpha used to clip ##
  fClipMatrix transforms fClipMask before it clips Layer. If
  fClipMask describes a translucent gradient, it may be scaled and rotated
  without introducing artifacts. fClipMatrix may be nullptr.
##

#Member SaveLayerFlags          fSaveLayerFlags
#Line # creates with prior Layer contents ##
    fSaveLayerFlags are used to create Layer without transparency,
    and to create Layer with the ontents of the previous Layer.
##

#Example
#Height 160
#Description
Canvas Layer captures a red Anti_Aliased circle and a blue Aliased circle scaled
up by four. After drawing another red circle without scaling on top, the Layer is
transferred to the main canvas.
##
void draw(SkCanvas* canvas) {
    SkPaint redPaint, bluePaint;
    redPaint.setAntiAlias(true);
    redPaint.setColor(SK_ColorRED);
    canvas->drawCircle(21, 21, 8, redPaint);
    bluePaint.setColor(SK_ColorBLUE);
    canvas->drawCircle(31, 21, 8, bluePaint);
    SkMatrix matrix;
    matrix.setScale(4, 4);
    auto scaler = SkImageFilter::MakeMatrixFilter(matrix, kNone_SkFilterQuality, nullptr);
    SkCanvas::SaveLayerRec saveLayerRec(nullptr, nullptr, scaler.get(), 0);
    canvas->saveLayer(saveLayerRec);
    canvas->drawCircle(125, 85, 8, redPaint);
    canvas->restore();
}
##

#Subtopic Constructors
##

#Method SaveLayerRec()
#Line # constructs SaveLayerRec ##
#Populate

#Example
    SkCanvas::SaveLayerRec rec1;
    rec1.fSaveLayerFlags = SkCanvas::kInitWithPrevious_SaveLayerFlag;
    SkCanvas::SaveLayerRec rec2(nullptr, nullptr, SkCanvas::kInitWithPrevious_SaveLayerFlag);
    SkDebugf("rec1 %c= rec2\n", rec1.fBounds == rec2.fBounds
            && rec1.fPaint == rec2.fPaint
            && rec1.fBackdrop == rec2.fBackdrop
            && rec1.fSaveLayerFlags == rec2.fSaveLayerFlags ? '=' : '!');
    #StdOut
        rec1 == rec2
    ##
##

#SeeAlso save restore saveLayer saveLayerAlpha

##

#Method SaveLayerRec(const SkRect* bounds, const SkPaint* paint, SaveLayerFlags saveLayerFlags = 0)
#Populate

#Example
    SkCanvas::SaveLayerRec rec1;
    SkCanvas::SaveLayerRec rec2(nullptr, nullptr);
    SkDebugf("rec1 %c= rec2\n", rec1.fBounds == rec2.fBounds
            && rec1.fPaint == rec2.fPaint
            && rec1.fBackdrop == rec2.fBackdrop
            && rec1.fSaveLayerFlags == rec2.fSaveLayerFlags ? '=' : '!');
    #StdOut
        rec1 == rec2
    ##
##

#SeeAlso save restore saveLayer saveLayerAlpha

##

#Method SaveLayerRec(const SkRect* bounds, const SkPaint* paint, const SkImageFilter* backdrop,
                     SaveLayerFlags saveLayerFlags)
#Populate

#Example
    SkCanvas::SaveLayerRec rec1;
    SkCanvas::SaveLayerRec rec2(nullptr, nullptr, nullptr, 0);
    SkDebugf("rec1 %c= rec2\n", rec1.fBounds == rec2.fBounds
            && rec1.fPaint == rec2.fPaint
            && rec1.fBackdrop == rec2.fBackdrop
            && rec1.fSaveLayerFlags == rec2.fSaveLayerFlags ? '=' : '!');
    #StdOut
        rec1 == rec2
    ##
##

#SeeAlso save restore saveLayer saveLayerAlpha

##

#Struct ##

#Subtopic ##

#Method int saveLayer(const SaveLayerRec& layerRec)

#In Layer
#Populate

#Example
#Description
The example draws an image, and saves it into a Layer with kInitWithPrevious_SaveLayerFlag.
Next it punches a hole in Layer and restore with SkBlendMode::kPlus.
Where Layer was cleared, the original image will draw unchanged.
Outside of the circle the mandrill is brightened.
##
    #Image 3
    // sk_sp<SkImage> image = GetResourceAsImage("images/mandrill_256.png");
    canvas->drawImage(image, 0, 0, nullptr);
    SkCanvas::SaveLayerRec rec;
    SkPaint paint;
    paint.setBlendMode(SkBlendMode::kPlus);
    rec.fSaveLayerFlags = SkCanvas::kInitWithPrevious_SaveLayerFlag;
    rec.fPaint = &paint;
    canvas->saveLayer(rec);
    paint.setBlendMode(SkBlendMode::kClear);
    canvas->drawCircle(128, 128, 96, paint);
    canvas->restore();
##

#ToDo above example needs to replace GetResourceAsImage with way to select image in fiddle ##

#SeeAlso save restore saveLayer saveLayerAlpha

##

#Subtopic Layer ##

# ------------------------------------------------------------------------------
#Subtopic Matrix
#Line # coordinate transformation ##

#Method void translate(SkScalar dx, SkScalar dy)

#In Matrix
#Line # translates Matrix ##
#Populate

#Example
#Height 128
#Description
scale() followed by translate() produces different results from translate() followed
by scale().

The blue stroke follows translate of (50, 50); a black
fill follows scale of (2, 1/2.f). After restoring the clip, which resets
Matrix, a red frame follows the same scale of (2, 1/2.f); a gray fill
follows translate of (50, 50).
##
void draw(SkCanvas* canvas) {
    SkPaint filledPaint;
    SkPaint outlinePaint;
    outlinePaint.setStyle(SkPaint::kStroke_Style);
    outlinePaint.setColor(SK_ColorBLUE);
    canvas->save();
    canvas->translate(50, 50);
    canvas->drawCircle(28, 28, 15, outlinePaint);  // blue center: (50+28, 50+28)
    canvas->scale(2, 1/2.f);
    canvas->drawCircle(28, 28, 15, filledPaint);   // black center: (50+(28*2), 50+(28/2))
    canvas->restore();
    filledPaint.setColor(SK_ColorGRAY);
    outlinePaint.setColor(SK_ColorRED);
    canvas->scale(2, 1/2.f);
    canvas->drawCircle(28, 28, 15, outlinePaint);  // red center: (28*2, 28/2)
    canvas->translate(50, 50);
    canvas->drawCircle(28, 28, 15, filledPaint);   // gray center: ((50+28)*2, (50+28)/2)
}
##

#SeeAlso concat() scale() skew() rotate() setMatrix

##

# ------------------------------------------------------------------------------

#Method void scale(SkScalar sx, SkScalar sy)

#In Matrix
#Line # scales Matrix ##
#Populate

#Example
#Height 160
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkRect rect = { 10, 20, 60, 120 };
    canvas->translate(20, 20);
    canvas->drawRect(rect, paint);
    canvas->scale(2, .5f);
    paint.setColor(SK_ColorGRAY);
    canvas->drawRect(rect, paint);
}
##

#SeeAlso concat() translate() skew() rotate() setMatrix

##

# ------------------------------------------------------------------------------

#Method void rotate(SkScalar degrees)

#In Matrix
#Line # rotates Matrix ##
#Populate

#Example
#Description
Draw clock hands at time 5:10. The hour hand and minute hand point up and
are rotated clockwise.
##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setStyle(SkPaint::kStroke_Style);
    canvas->translate(128, 128);
    canvas->drawCircle(0, 0, 60, paint);
    canvas->save();
    canvas->rotate(10 * 360 / 60);   // 10 minutes of 60 scaled to 360 degrees
    canvas->drawLine(0, 0, 0, -50, paint);
    canvas->restore();
    canvas->rotate((5 + 10.f/60) * 360 / 12); // 5 and 10/60 hours of 12 scaled to 360 degrees
    canvas->drawLine(0, 0, 0, -30, paint);
}
##

#SeeAlso concat() translate() skew() scale() setMatrix

##

# ------------------------------------------------------------------------------

#Method void rotate(SkScalar degrees, SkScalar px, SkScalar py)

#In Matrix
#Populate

#Example
#Height 192
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkFont font(nullptr, 96);
    canvas->drawString("A1", 130, 100, font, paint);
    canvas->rotate(180, 130, 100);
    canvas->drawString("A1", 130, 100, font, paint);
}
##

#SeeAlso concat() translate() skew() scale() setMatrix

##

# ------------------------------------------------------------------------------

#Method void skew(SkScalar sx, SkScalar sy)

#In Matrix
#Line # skews Matrix ##
#Populate

#Example
    #Description
        Black text mimics an oblique text style by using a negative skew on x-axis
        that shifts the geometry to the right as the y-axis values decrease.
        Red text uses a positive skew on y-axis to shift the geometry down
        as the x-axis values increase.
        Blue text combines sx and sy skew to rotate and scale.
    ##
    SkPaint paint;
    SkFont font(nullptr, 128);
    canvas->translate(30, 130);
    canvas->save();
    canvas->skew(-.5, 0);
    canvas->drawString("A1", 0, 0, font, paint);
    canvas->restore();
    canvas->save();
    canvas->skew(0, .5);
    paint.setColor(SK_ColorRED);
    canvas->drawString("A1", 0, 0, font, paint);
    canvas->restore();
    canvas->skew(-.5, .5);
    paint.setColor(SK_ColorBLUE);
    canvas->drawString("A1", 0, 0, font, paint);
##

#SeeAlso concat() translate() rotate() scale() setMatrix

##

# ------------------------------------------------------------------------------

#Method void concat(const SkMatrix& matrix)

#In Matrix
#Line # multiplies Matrix by Matrix ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkFont font(nullptr, 80);
    font.setScaleX(.3);
    SkMatrix matrix;
    SkRect rect[2] = {{ 10, 20, 90, 110 }, { 40, 130, 140, 180 }};
    matrix.setRectToRect(rect[0], rect[1], SkMatrix::kFill_ScaleToFit);
    canvas->drawRect(rect[0], paint);
    canvas->drawRect(rect[1], paint);
    paint.setColor(SK_ColorWHITE);
    canvas->drawString("Here", rect[0].fLeft + 10, rect[0].fBottom - 10, font, paint);
    canvas->concat(matrix);
    canvas->drawString("There", rect[0].fLeft + 10, rect[0].fBottom - 10, font, paint);
}
##

#SeeAlso translate() rotate() scale() skew() setMatrix

##

# ------------------------------------------------------------------------------

#Method void setMatrix(const SkMatrix& matrix)

#In Matrix
#Line # sets Matrix ##
#Populate

#Example
#Height 128
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkFont font;
    canvas->scale(4, 6);
    canvas->drawString("truth", 2, 10, font, paint);
    SkMatrix matrix;
    matrix.setScale(2.8f, 6);
    canvas->setMatrix(matrix);
    canvas->drawString("consequences", 2, 20, font, paint);
}
##

#SeeAlso resetMatrix concat() translate() rotate() scale() skew()

##

# ------------------------------------------------------------------------------

#Method void resetMatrix()

#In Matrix
#Line # resets Matrix to identity ##
#Populate

#Example
#Height 128
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkFont font;
    canvas->scale(4, 6);
    canvas->drawString("truth", 2, 10, font, paint);
    canvas->resetMatrix();
    canvas->scale(2.8f, 6);
    canvas->drawString("consequences", 2, 20, font, paint);
}
##

#SeeAlso setMatrix concat() translate() rotate() scale() skew()

##

# ------------------------------------------------------------------------------

#Method const SkMatrix& getTotalMatrix() const

#In Matrix
#Line # returns Matrix ##
#Populate

#Example
    SkDebugf("isIdentity %s\n", canvas->getTotalMatrix().isIdentity() ? "true" : "false");
    #StdOut
        isIdentity true
    ##
##

#SeeAlso setMatrix resetMatrix concat()

##

#Subtopic Matrix ##

# ------------------------------------------------------------------------------
#Subtopic Clip
#Line # stack of clipping Paths ##

Clip is built from a stack of clipping paths. Each Path in the
stack can be constructed from one or more Path_Contour elements. The
Path_Contour may be composed of any number of Path_Verb segments. Each
Path_Contour forms a closed area; Path_Fill_Type defines the area enclosed
by Path_Contour.

Clip stack of Path elements successfully restrict the Path area. Each
Path is transformed by Matrix, then intersected with or subtracted from the
prior Clip to form the replacement Clip. Use SkClipOp::kDifference
to subtract Path from Clip; use SkClipOp::kIntersect to intersect Path
with Clip.

A clipping Path may be Anti_Aliased; if Path, after transformation, is
composed of horizontal and vertical lines, clearing Anti_Alias allows whole pixels
to either be inside or outside the clip. The fastest drawing has a Aliased,
rectangular clip.

If clipping Path has Anti_Alias set, clip may partially clip a pixel, requiring
that drawing blend partially with the destination along the edge. A rotated
rectangular Anti_Aliased clip looks smoother but draws slower.

Clip can combine with Rect and Round_Rect primitives; like
Path, these are transformed by Matrix before they are combined with Clip.

Clip can combine with Region. Region is assumed to be in Device coordinates
and is unaffected by Matrix.

#Example
#Height 90
    #Description
        Draw a red circle with an Aliased clip and an Anti_Aliased clip.
        Use an image filter to zoom into the pixels drawn.
        The edge of the Aliased clip fully draws pixels in the red circle.
        The edge of the Anti_Aliased clip partially draws pixels in the red circle.
    ##
    SkPaint redPaint, scalePaint;
    redPaint.setAntiAlias(true);
    redPaint.setColor(SK_ColorRED);
    canvas->save();
    for (bool antialias : { false, true } ) {
        canvas->save();
        canvas->clipRect(SkRect::MakeWH(19.5f, 11.5f), antialias);
        canvas->drawCircle(17, 11, 8, redPaint);
        canvas->restore();
        canvas->translate(16, 0);
    }
    canvas->restore();
    SkMatrix matrix;
    matrix.setScale(6, 6);
    scalePaint.setImageFilter(
            SkImageFilter::MakeMatrixFilter(matrix, kNone_SkFilterQuality, nullptr));
    SkCanvas::SaveLayerRec saveLayerRec(
            nullptr, &scalePaint, SkCanvas::kInitWithPrevious_SaveLayerFlag);
    canvas->saveLayer(saveLayerRec);
    canvas->restore();
##

#Method void clipRect(const SkRect& rect, SkClipOp op, bool doAntiAlias)

#In Clip
#Line # combines Clip with Rect ##
#Populate

#Example
#Height 128
void draw(SkCanvas* canvas) {
    canvas->rotate(10);
    SkPaint paint;
    paint.setAntiAlias(true);
    for (auto alias: { false, true } ) {
        canvas->save();
        canvas->clipRect(SkRect::MakeWH(90, 80), SkClipOp::kIntersect, alias);
        canvas->drawCircle(100, 60, 60, paint);
        canvas->restore();
        canvas->translate(80, 0);
    }
}
##

#SeeAlso clipRRect clipPath clipRegion

##

#Method void clipRect(const SkRect& rect, SkClipOp op)

#In Clip
#Populate

#Example
#Height 192
#Width 280
void draw(SkCanvas* canvas) {
    SkPaint paint;
    for (SkClipOp op: { SkClipOp::kIntersect, SkClipOp::kDifference } ) {
        canvas->save();
        canvas->clipRect(SkRect::MakeWH(90, 120), op, false);
        canvas->drawCircle(100, 100, 60, paint);
        canvas->restore();
        canvas->translate(80, 0);
    }
}
##

#SeeAlso clipRRect clipPath clipRegion

##

#Method void clipRect(const SkRect& rect, bool doAntiAlias = false)

#In Clip
#Populate

#Example
#Height 133
    #Description
        A circle drawn in pieces looks uniform when drawn Aliased.
        The same circle pieces blend with pixels more than once when Anti_Aliased,
        visible as a thin pair of lines through the right circle.
    ##
void draw(SkCanvas* canvas) {
    canvas->clear(SK_ColorWHITE);
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setColor(0x8055aaff);
    SkRect clipRect = { 0, 0, 87.4f, 87.4f };
    for (auto alias: { false, true } ) {
        canvas->save();
        canvas->clipRect(clipRect, SkClipOp::kIntersect, alias);
        canvas->drawCircle(67, 67, 60, paint);
        canvas->restore();
        canvas->save();
        canvas->clipRect(clipRect, SkClipOp::kDifference, alias);
        canvas->drawCircle(67, 67, 60, paint);
        canvas->restore();
        canvas->translate(120, 0);
    }
}
##

#SeeAlso clipRRect clipPath clipRegion

##

#Method void clipRRect(const SkRRect& rrect, SkClipOp op, bool doAntiAlias)

#In Clip
#Line # combines Clip with Round_Rect ##
#Populate

#Example
#Height 128
void draw(SkCanvas* canvas) {
    canvas->clear(SK_ColorWHITE);
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setColor(0x8055aaff);
    SkRRect oval;
    oval.setOval({10, 20, 90, 100});
    canvas->clipRRect(oval, SkClipOp::kIntersect, true);
    canvas->drawCircle(70, 100, 60, paint);
}
##

#SeeAlso clipRect clipPath clipRegion

##

#Method void clipRRect(const SkRRect& rrect, SkClipOp op)

#In Clip
#Populate

#Example
#Height 128
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setColor(0x8055aaff);
    auto oval = SkRRect::MakeOval({10, 20, 90, 100});
    canvas->clipRRect(oval, SkClipOp::kIntersect);
    canvas->drawCircle(70, 100, 60, paint);
}
##

#SeeAlso clipRect clipPath clipRegion

##

#Method void clipRRect(const SkRRect& rrect, bool doAntiAlias = false)

#In Clip
#Populate

#Example
#Height 128
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    auto oval = SkRRect::MakeRectXY({10, 20, 90, 100}, 9, 13);
    canvas->clipRRect(oval, true);
    canvas->drawCircle(70, 100, 60, paint);
}
##

#SeeAlso clipRect clipPath clipRegion

##

#Method void clipPath(const SkPath& path, SkClipOp op, bool doAntiAlias)

#In Clip
#Line # combines Clip with Path ##
#Populate

#Example
#Description
Top figure uses SkPath::kInverseWinding_FillType and SkClipOp::kDifference;
area outside clip is subtracted from circle.

Bottom figure uses SkPath::kWinding_FillType and SkClipOp::kIntersect;
area inside clip is intersected with circle.
##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    SkPath path;
    path.addRect({20, 30, 100, 110});
    path.setFillType(SkPath::kInverseWinding_FillType);
    canvas->save();
    canvas->clipPath(path, SkClipOp::kDifference, false);
    canvas->drawCircle(70, 100, 60, paint);
    canvas->restore();
    canvas->translate(100, 100);
    path.setFillType(SkPath::kWinding_FillType);
    canvas->clipPath(path, SkClipOp::kIntersect, false);
    canvas->drawCircle(70, 100, 60, paint);
}
##

#SeeAlso clipRect clipRRect clipRegion

##

#Method void clipPath(const SkPath& path, SkClipOp op)

#In Clip
#Populate

#Example
#Description
Overlapping Rects form a clip. When clip Path_Fill_Type is set to
SkPath::kWinding_FillType, the overlap is included. Set to
SkPath::kEvenOdd_FillType, the overlap is excluded and forms a hole.
##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    SkPath path;
    path.addRect({20, 15, 100, 95});
    path.addRect({50, 65, 130, 135});
    path.setFillType(SkPath::kWinding_FillType);
    canvas->save();
    canvas->clipPath(path, SkClipOp::kIntersect);
    canvas->drawCircle(70, 85, 60, paint);
    canvas->restore();
    canvas->translate(100, 100);
    path.setFillType(SkPath::kEvenOdd_FillType);
    canvas->clipPath(path, SkClipOp::kIntersect);
    canvas->drawCircle(70, 85, 60, paint);
}
##

#SeeAlso clipRect clipRRect clipRegion

##

#Method void clipPath(const SkPath& path, bool doAntiAlias = false)

#In Clip
#Populate

#Example
#Height 212
#Description
Clip loops over itself covering its center twice. When clip Path_Fill_Type
is set to SkPath::kWinding_FillType, the overlap is included. Set to
SkPath::kEvenOdd_FillType, the overlap is excluded and forms a hole.
##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    SkPath path;
    SkPoint poly[] = {{20, 20}, { 80, 20}, { 80,  80}, {40,  80},
                      {40, 40}, {100, 40}, {100, 100}, {20, 100}};
    path.addPoly(poly, SK_ARRAY_COUNT(poly), true);
    path.setFillType(SkPath::kWinding_FillType);
    canvas->save();
    canvas->clipPath(path, SkClipOp::kIntersect);
    canvas->drawCircle(50, 50, 45, paint);
    canvas->restore();
    canvas->translate(100, 100);
    path.setFillType(SkPath::kEvenOdd_FillType);
    canvas->clipPath(path, SkClipOp::kIntersect);
    canvas->drawCircle(50, 50, 45, paint);
}
##

#SeeAlso clipRect clipRRect clipRegion

##

# ------------------------------------------------------------------------------

#Method void clipRegion(const SkRegion& deviceRgn, SkClipOp op = SkClipOp::kIntersect)

#In Clip
#Line # combines Clip with Region ##
#Populate

#Example
#Description
    region is unaffected by canvas rotation; iRect is affected by canvas rotation.
    Both clips are Aliased; this is not noticeable on Region clip because it
    aligns to pixel boundaries.
##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    SkIRect iRect = {30, 40, 120, 130 };
    SkRegion region(iRect);
    canvas->rotate(10);
    canvas->save();
    canvas->clipRegion(region, SkClipOp::kIntersect);
    canvas->drawCircle(50, 50, 45, paint);
    canvas->restore();
    canvas->translate(100, 100);
    canvas->clipRect(SkRect::Make(iRect), SkClipOp::kIntersect);
    canvas->drawCircle(50, 50, 45, paint);
}
##

#SeeAlso clipRect clipRRect clipPath

##

#Method bool quickReject(const SkRect& rect) const

#In Clip
#Line # returns if Rect is outside Clip ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkRect testRect = {30, 30, 120, 129 };
    SkRect clipRect = {30, 130, 120, 230 };
    canvas->save();
    canvas->clipRect(clipRect);
    SkDebugf("quickReject %s\n", canvas->quickReject(testRect) ? "true" : "false");
    canvas->restore();
    canvas->rotate(10);
    canvas->clipRect(clipRect);
    SkDebugf("quickReject %s\n", canvas->quickReject(testRect) ? "true" : "false");
}
    #StdOut
        quickReject true
        quickReject false
    ##
##

#SeeAlso getLocalClipBounds getTotalMatrix SkBitmap::drawsNothing

##

#Method bool quickReject(const SkPath& path) const

#In Clip
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkPoint testPoints[] = {{30,  30}, {120,  30}, {120, 129} };
    SkPoint clipPoints[] = {{30, 130}, {120, 130}, {120, 230} };
    SkPath testPath, clipPath;
    testPath.addPoly(testPoints, SK_ARRAY_COUNT(testPoints), true);
    clipPath.addPoly(clipPoints, SK_ARRAY_COUNT(clipPoints), true);
    canvas->save();
    canvas->clipPath(clipPath);
    SkDebugf("quickReject %s\n", canvas->quickReject(testPath) ? "true" : "false");
    canvas->restore();
    canvas->rotate(10);
    canvas->clipPath(clipPath);
    SkDebugf("quickReject %s\n", canvas->quickReject(testPath) ? "true" : "false");
    #StdOut
        quickReject true
        quickReject false
    ##
}
##

#SeeAlso getLocalClipBounds getTotalMatrix SkBitmap::drawsNothing

##

#Method SkRect getLocalClipBounds() const

#In Clip
#Line # returns Clip bounds in source coordinates ##
#Populate

#Example
    #Description
        Initial bounds is device bounds outset by 1 on all sides.
        Clipped bounds is clipPath bounds outset by 1 on all sides.
        Scaling the canvas by two on both axes scales the local bounds by 1/2
        on both axes.
    ##
    SkCanvas local(256, 256);
    canvas = &local;
    SkRect bounds = canvas->getLocalClipBounds();
    SkDebugf("left:%g  top:%g  right:%g  bottom:%g\n",
            bounds.fLeft, bounds.fTop, bounds.fRight, bounds.fBottom);
    SkPoint clipPoints[]  = {{30, 130}, {120, 130}, {120, 230} };
    SkPath clipPath;
    clipPath.addPoly(clipPoints, SK_ARRAY_COUNT(clipPoints), true);
    canvas->clipPath(clipPath);
    bounds = canvas->getLocalClipBounds();
    SkDebugf("left:%g  top:%g  right:%g  bottom:%g\n",
            bounds.fLeft, bounds.fTop, bounds.fRight, bounds.fBottom);
    canvas->scale(2, 2);
    bounds = canvas->getLocalClipBounds();
    SkDebugf("left:%g  top:%g  right:%g  bottom:%g\n",
            bounds.fLeft, bounds.fTop, bounds.fRight, bounds.fBottom);
    #StdOut
        left:-1  top:-1  right:257  bottom:257
        left:29  top:129  right:121  bottom:231
        left:14.5  top:64.5  right:60.5  bottom:115.5
    ##
##

# local canvas in example works around bug in fiddle ##
#Bug 6524
#SeeAlso getDeviceClipBounds getBaseLayerSize quickReject

##

#Method bool getLocalClipBounds(SkRect* bounds) const

#In Clip
#Populate

#Example
    void draw(SkCanvas* canvas) {
        SkCanvas local(256, 256);
        canvas = &local;
        SkRect bounds;
        SkDebugf("local bounds empty = %s\n", canvas->getLocalClipBounds(&bounds)
                 ? "false" : "true");
        SkPath path;
        canvas->clipPath(path);
        SkDebugf("local bounds empty = %s\n", canvas->getLocalClipBounds(&bounds)
                 ? "false" : "true");
    }
    #StdOut
        local bounds empty = false
        local bounds empty = true
    ##
##

# local canvas in example works around bug in fiddle ##
#Bug 6524
#SeeAlso getDeviceClipBounds getBaseLayerSize quickReject

##

#Method SkIRect getDeviceClipBounds() const

#In Clip
#Line # returns IRect bounds of Clip ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    #Description
        Initial bounds is device bounds, not outset.
        Clipped bounds is clipPath bounds, not outset.
        Scaling the canvas by 1/2 on both axes scales the device bounds by 1/2
        on both axes.
    ##
    SkCanvas device(256, 256);
    canvas = &device;
    SkIRect bounds = canvas->getDeviceClipBounds();
    SkDebugf("left:%d  top:%d  right:%d  bottom:%d\n",
            bounds.fLeft, bounds.fTop, bounds.fRight, bounds.fBottom);
    SkPoint clipPoints[]  = {{30, 130}, {120, 130}, {120, 230} };
    SkPath clipPath;
    clipPath.addPoly(clipPoints, SK_ARRAY_COUNT(clipPoints), true);
    canvas->save();
    canvas->clipPath(clipPath);
    bounds = canvas->getDeviceClipBounds();
    SkDebugf("left:%d  top:%d  right:%d  bottom:%d\n",
            bounds.fLeft, bounds.fTop, bounds.fRight, bounds.fBottom);
    canvas->restore();
    canvas->scale(1.f/2, 1.f/2);
    canvas->clipPath(clipPath);
    bounds = canvas->getDeviceClipBounds();
    SkDebugf("left:%d  top:%d  right:%d  bottom:%d\n",
            bounds.fLeft, bounds.fTop, bounds.fRight, bounds.fBottom);
    #StdOut
        left:0  top:0  right:256  bottom:256
        left:30  top:130  right:120  bottom:230
        left:15  top:65  right:60  bottom:115
    ##
}
##

#ToDo some confusion on why with an identity Matrix local and device are different ##
#SeeAlso getLocalClipBounds getBaseLayerSize quickReject

# device canvas in example works around bug in fiddle ##
#Bug 6524

##

#Method bool getDeviceClipBounds(SkIRect* bounds) const

#In Clip
#Populate

#Example
    void draw(SkCanvas* canvas) {
        SkIRect bounds;
        SkDebugf("device bounds empty = %s\n", canvas->getDeviceClipBounds(&bounds)
                 ? "false" : "true");
        SkPath path;
        canvas->clipPath(path);
        SkDebugf("device bounds empty = %s\n", canvas->getDeviceClipBounds(&bounds)
                 ? "false" : "true");
    }
    #StdOut
        device bounds empty = false
        device bounds empty = true
    ##
##

#SeeAlso getLocalClipBounds getBaseLayerSize quickReject

##

#Subtopic Clip ##

# ------------------------------------------------------------------------------
#Subtopic Draw
#Line # draws into Canvas ##
##

#Method void drawColor(SkColor color, SkBlendMode mode = SkBlendMode::kSrcOver)
#In Draw
#Line # fills Clip with Color and Blend_Mode ##
#Populate

#Example
    canvas->drawColor(SK_ColorRED);
    canvas->clipRect(SkRect::MakeWH(150, 150));
    canvas->drawColor(SkColorSetARGB(0x80, 0x00, 0xFF, 0x00), SkBlendMode::kPlus);
    canvas->clipRect(SkRect::MakeWH(75, 75));
    canvas->drawColor(SkColorSetARGB(0x80, 0x00, 0x00, 0xFF), SkBlendMode::kPlus);
##

#SeeAlso clear SkBitmap::erase drawPaint

##

# ------------------------------------------------------------------------------

#Method void clear(SkColor color)
#In Draw
#Line # fills Clip with Color ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    canvas->save();
    canvas->clipRect(SkRect::MakeWH(256, 128));
    canvas->clear(SkColorSetARGB(0x80, 0xFF, 0x00, 0x00));
    canvas->restore();
    canvas->save();
    canvas->clipRect(SkRect::MakeWH(150, 192));
    canvas->clear(SkColorSetARGB(0x80, 0x00, 0xFF, 0x00));
    canvas->restore();
    canvas->clipRect(SkRect::MakeWH(75, 256));
    canvas->clear(SkColorSetARGB(0x80, 0x00, 0x00, 0xFF));
}
##

#SeeAlso drawColor SkBitmap::erase drawPaint

##

# ------------------------------------------------------------------------------

#Method void discard()
#In Utility
#Line # makes Canvas contents undefined ##
#Populate

#NoExample
##

#SeeAlso flush() GrContext::abandonContext

##

# ------------------------------------------------------------------------------

#Method void drawPaint(const SkPaint& paint)
#In Draw
#Line # fills Clip with Paint ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkColor     colors[] = { SK_ColorRED, SK_ColorGREEN, SK_ColorBLUE };
    SkScalar    pos[] = { 0, SK_Scalar1/2, SK_Scalar1 };
    SkPaint     paint;
    paint.setShader(SkGradientShader::MakeSweep(256, 256, colors, pos, SK_ARRAY_COUNT(colors)));
    canvas->drawPaint(paint);
}
##

#SeeAlso clear drawColor SkBitmap::erase

##

# ------------------------------------------------------------------------------

#Enum PointMode
#Line # sets drawPoints options ##

#Code
#Populate
##

Selects if an array of points are drawn as discrete points, as lines, or as
an open polygon.

#Const kPoints_PointMode 0
#Line # draw each point separately ##
##

#Const kLines_PointMode 1
#Line # draw each pair of points as a line segment ##
##

#Const kPolygon_PointMode 2
#Line # draw the array of points as a open polygon ##
##

#Example
    #Description
        The upper left corner shows three squares when drawn as points.
        The upper right corner shows one line; when drawn as lines, two points are required per line.
        The lower right corner shows two lines; when draw as polygon, no miter is drawn at the corner.
        The lower left corner shows two lines with a miter when path contains polygon.
    ##
void draw(SkCanvas* canvas) {
  SkPaint paint;
  paint.setStyle(SkPaint::kStroke_Style);
  paint.setStrokeWidth(10);
  SkPoint points[] = {{64, 32}, {96, 96}, {32, 96}};
  canvas->drawPoints(SkCanvas::kPoints_PointMode, 3, points, paint);
  canvas->translate(128, 0);
  canvas->drawPoints(SkCanvas::kLines_PointMode, 3, points, paint);
  canvas->translate(0, 128);
  canvas->drawPoints(SkCanvas::kPolygon_PointMode, 3, points, paint);
  SkPath path;
  path.addPoly(points, 3, false);
  canvas->translate(-128, 0);
  canvas->drawPath(path, paint);
}
##

#SeeAlso drawLine drawPoint drawPath

##

# ------------------------------------------------------------------------------

#Method void drawPoints(PointMode mode, size_t count, const SkPoint pts[], const SkPaint& paint)
#In Draw
#Line # draws array as points, lines, polygon ##
#Populate

#Example
#Height 200
    #Description
    #List
    # The first column draws points. ##
    # The second column draws points as lines. ##
    # The third column draws points as a polygon. ##
    # The fourth column draws points as a polygonal path. ##
    # The first row uses a round cap and round join. ##
    # The second row uses a square cap and a miter join. ##
    # The third row uses a butt cap and a bevel join. ##
    ##
    The transparent color makes multiple line draws visible;
    the path is drawn all at once.
    ##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStroke_Style);
    paint.setStrokeWidth(10);
    paint.setColor(0x80349a45);
    const SkPoint points[] = {{32, 16}, {48, 48}, {16, 32}};
    const SkPaint::Join join[] = { SkPaint::kRound_Join,
                                   SkPaint::kMiter_Join,
                                   SkPaint::kBevel_Join };
    int joinIndex = 0;
    SkPath path;
    path.addPoly(points, 3, false);
    for (const auto cap : { SkPaint::kRound_Cap, SkPaint::kSquare_Cap, SkPaint::kButt_Cap } ) {
        paint.setStrokeCap(cap);
        paint.setStrokeJoin(join[joinIndex++]);
        for (const auto mode : { SkCanvas::kPoints_PointMode,
                                 SkCanvas::kLines_PointMode,
                                 SkCanvas::kPolygon_PointMode } ) {
            canvas->drawPoints(mode, 3, points, paint);
            canvas->translate(64, 0);
        }
        canvas->drawPath(path, paint);
        canvas->translate(-192, 64);
    }
}
##

#SeeAlso drawLine drawPoint drawPath

##

# ------------------------------------------------------------------------------

#Method void drawPoint(SkScalar x, SkScalar y, const SkPaint& paint)
#In Draw
#Line # draws point at (x, y) position ##
#Populate

#Example
void draw(SkCanvas* canvas) {
  SkPaint paint;
  paint.setAntiAlias(true);
  paint.setColor(0x80349a45);
  paint.setStyle(SkPaint::kStroke_Style);
  paint.setStrokeWidth(100);
  paint.setStrokeCap(SkPaint::kRound_Cap);
  canvas->scale(1, 1.2f);
  canvas->drawPoint(64, 96, paint);
  canvas->scale(.6f, .8f);
  paint.setColor(SK_ColorWHITE);
  canvas->drawPoint(106, 120, paint);
}
##

#SeeAlso drawPoints drawCircle drawRect drawLine drawPath

##

#Method void drawPoint(SkPoint p, const SkPaint& paint)
#Populate

#Example
void draw(SkCanvas* canvas) {
  SkPaint paint;
  paint.setAntiAlias(true);
  paint.setColor(0x80349a45);
  paint.setStyle(SkPaint::kStroke_Style);
  paint.setStrokeWidth(100);
  paint.setStrokeCap(SkPaint::kSquare_Cap);
  canvas->scale(1, 1.2f);
  canvas->drawPoint({64, 96}, paint);
  canvas->scale(.6f, .8f);
  paint.setColor(SK_ColorWHITE);
  canvas->drawPoint(106, 120, paint);
}
##

#SeeAlso drawPoints drawCircle drawRect drawLine drawPath

##

# ------------------------------------------------------------------------------

#Method void drawLine(SkScalar x0, SkScalar y0, SkScalar x1, SkScalar y1, const SkPaint& paint)
#In Draw
#Line # draws line segment between two points ##
#Populate

#Example
  SkPaint paint;
  paint.setAntiAlias(true);
  paint.setColor(0xFF9a67be);
  paint.setStrokeWidth(20);
  canvas->skew(1, 0);
  canvas->drawLine(32, 96, 32, 160, paint);
  canvas->skew(-2, 0);
  canvas->drawLine(288, 96, 288, 160, paint);
##

#SeeAlso drawPoint drawCircle drawRect drawPath

##

#Method void drawLine(SkPoint p0, SkPoint p1, const SkPaint& paint)
#Populate

#Example
  SkPaint paint;
  paint.setAntiAlias(true);
  paint.setColor(0xFF9a67be);
  paint.setStrokeWidth(20);
  canvas->skew(1, 0);
  canvas->drawLine({32, 96}, {32, 160}, paint);
  canvas->skew(-2, 0);
  canvas->drawLine({288, 96}, {288, 160}, paint);
##

#SeeAlso drawPoint drawCircle drawRect drawPath

##

# ------------------------------------------------------------------------------

#Method void drawRect(const SkRect& rect, const SkPaint& paint)
#In Draw
#Line # draws Rect using Clip, Matrix, and Paint ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkPoint rectPts[] = { {64, 48}, {192, 160} };
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStroke_Style);
    paint.setStrokeWidth(20);
    paint.setStrokeJoin(SkPaint::kRound_Join);
    SkMatrix rotator;
    rotator.setRotate(30, 128, 128);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, SK_ColorYELLOW, SK_ColorMAGENTA } ) {
        paint.setColor(color);
        SkRect rect;
        rect.set(rectPts[0], rectPts[1]);
        canvas->drawRect(rect, paint);
        rotator.mapPoints(rectPts, 2);
    }
}
##

#SeeAlso drawIRect drawRRect drawRoundRect drawRegion drawPath drawLine

##

# ------------------------------------------------------------------------------

#Method void drawIRect(const SkIRect& rect, const SkPaint& paint)
#In Draw
#Line # draws IRect using Clip, Matrix, and Paint ##
#Populate

#Example
    SkIRect rect = { 64, 48, 192, 160 };
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStroke_Style);
    paint.setStrokeWidth(20);
    paint.setStrokeJoin(SkPaint::kRound_Join);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, SK_ColorYELLOW, SK_ColorMAGENTA } ) {
        paint.setColor(color);
        canvas->drawIRect(rect, paint);
        canvas->rotate(30, 128, 128);
    }
##

#SeeAlso drawRect drawRRect drawRoundRect drawRegion drawPath drawLine

##

# ------------------------------------------------------------------------------

#Method void drawRegion(const SkRegion& region, const SkPaint& paint)
#In Draw
#Line # draws Region using Clip, Matrix, and Paint ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkRegion region;
    region.op( 10, 10, 50, 50, SkRegion::kUnion_Op);
    region.op( 10, 50, 90, 90, SkRegion::kUnion_Op);
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStroke_Style);
    paint.setStrokeWidth(20);
    paint.setStrokeJoin(SkPaint::kRound_Join);
    canvas->drawRegion(region, paint);
}
##

#SeeAlso drawRect drawIRect drawPath

##

# ------------------------------------------------------------------------------

#Method void drawOval(const SkRect& oval, const SkPaint& paint)
#In Draw
#Line # draws Oval using Clip, Matrix, and Paint ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    canvas->clear(0xFF3f5f9f);
    SkColor  kColor1 = SkColorSetARGB(0xff, 0xff, 0x7f, 0);
    SkColor  g1Colors[] = { kColor1, SkColorSetA(kColor1, 0x20) };
    SkPoint  g1Points[] = { { 0, 0 }, { 0, 100 } };
    SkScalar pos[] = { 0.2f, 1.0f };
    SkRect bounds = SkRect::MakeWH(80, 70);
    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setShader(SkGradientShader::MakeLinear(g1Points, g1Colors, pos, SK_ARRAY_COUNT(g1Colors),
            SkShader::kClamp_TileMode));
    canvas->drawOval(bounds , paint);
}
##

#SeeAlso drawCircle drawPoint drawPath drawRRect drawRoundRect

##

# ------------------------------------------------------------------------------

#Method void drawRRect(const SkRRect& rrect, const SkPaint& paint)
#In Draw
#Line # draws Round_Rect using Clip, Matrix, and Paint ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    SkRect outer = {30, 40, 210, 220};
    SkRect radii = {30, 50, 70, 90 };
    SkRRect rRect;
    rRect.setNinePatch(outer, radii.fLeft, radii.fTop, radii.fRight, radii.fBottom);
    canvas->drawRRect(rRect, paint);
    paint.setColor(SK_ColorWHITE);
    canvas->drawLine(outer.fLeft + radii.fLeft, outer.fTop,
                     outer.fLeft + radii.fLeft, outer.fBottom, paint);
    canvas->drawLine(outer.fRight - radii.fRight, outer.fTop,
                     outer.fRight - radii.fRight, outer.fBottom, paint);
    canvas->drawLine(outer.fLeft,  outer.fTop + radii.fTop,
                     outer.fRight, outer.fTop + radii.fTop, paint);
    canvas->drawLine(outer.fLeft,  outer.fBottom - radii.fBottom,
                     outer.fRight, outer.fBottom - radii.fBottom, paint);
}
##

#SeeAlso drawRect drawRoundRect drawDRRect drawCircle drawOval drawPath

##

# ------------------------------------------------------------------------------

#Method void drawDRRect(const SkRRect& outer, const SkRRect& inner, const SkPaint& paint)
#In Draw
#Line # draws double Round_Rect stroked or filled ##
#Populate

#Example
void draw(SkCanvas* canvas) {
   SkRRect outer = SkRRect::MakeRect({20, 40, 210, 200});
   SkRRect inner = SkRRect::MakeOval({60, 70, 170, 160});
   SkPaint paint;
   canvas->drawDRRect(outer, inner, paint);
}
##

#Example
#Description
    Outer Rect has no corner radii, but stroke join is rounded.
    Inner Round_Rect has corner radii; outset stroke increases radii of corners.
    Stroke join does not affect inner Round_Rect since it has no sharp corners.
##
void draw(SkCanvas* canvas) {
   SkRRect outer = SkRRect::MakeRect({20, 40, 210, 200});
   SkRRect inner = SkRRect::MakeRectXY({60, 70, 170, 160}, 10, 10);
   SkPaint paint;
   paint.setAntiAlias(true);
   paint.setStyle(SkPaint::kStroke_Style);
   paint.setStrokeWidth(20);
   paint.setStrokeJoin(SkPaint::kRound_Join);
   canvas->drawDRRect(outer, inner, paint);
   paint.setStrokeWidth(1);
   paint.setColor(SK_ColorWHITE);
   canvas->drawDRRect(outer, inner, paint);
}
##

#SeeAlso drawRect drawRoundRect drawRRect drawCircle drawOval drawPath

##

# ------------------------------------------------------------------------------

#Method void drawCircle(SkScalar cx, SkScalar cy, SkScalar radius, const SkPaint& paint)
#In Draw
#Line # draws Circle using Clip, Matrix, and Paint ##
#Populate

#Example
    void draw(SkCanvas* canvas) {
        SkPaint paint;
        paint.setAntiAlias(true);
        canvas->drawCircle(128, 128, 90, paint);
        paint.setColor(SK_ColorWHITE);
        canvas->drawCircle(86, 86, 20, paint);
        canvas->drawCircle(160, 76, 20, paint);
        canvas->drawCircle(140, 150, 35, paint);
    }
##

#SeeAlso drawOval drawRRect drawRoundRect drawPath drawArc drawPoint drawLine

##

#Method void drawCircle(SkPoint center, SkScalar radius, const SkPaint& paint)
#Populate

#Example
    void draw(SkCanvas* canvas) {
        SkPaint paint;
        paint.setAntiAlias(true);
        canvas->drawCircle(128, 128, 90, paint);
        paint.setColor(SK_ColorWHITE);
        canvas->drawCircle({86, 86}, 20, paint);
        canvas->drawCircle({160, 76}, 20, paint);
        canvas->drawCircle({140, 150}, 35, paint);
    }
##

#SeeAlso drawOval drawRRect drawRoundRect drawPath drawArc drawPoint drawLine

##

# ------------------------------------------------------------------------------

#Method void drawArc(const SkRect& oval, SkScalar startAngle, SkScalar sweepAngle,
                 bool useCenter, const SkPaint& paint)
#In Draw
#Line # draws Arc using Clip, Matrix, and Paint ##
#Populate

#Example
    void draw(SkCanvas* canvas) {
        SkPaint paint;
        paint.setAntiAlias(true);
        SkRect oval = { 4, 4, 60, 60};
        for (auto useCenter : { false, true } ) {
            for (auto style : { SkPaint::kFill_Style, SkPaint::kStroke_Style } ) {
                paint.setStyle(style);
                for (auto degrees : { 45, 90, 180, 360} ) {
                    canvas->drawArc(oval, 0, degrees , useCenter, paint);
                    canvas->translate(64, 0);
                }
                canvas->translate(-256, 64);
            }
        }
    }
##

#Example
#Height 64
    void draw(SkCanvas* canvas) {
        SkPaint paint;
        paint.setAntiAlias(true);
        paint.setStyle(SkPaint::kStroke_Style);
        paint.setStrokeWidth(4);
        SkRect oval = { 4, 4, 60, 60};
        float intervals[] = { 5, 5 };
        paint.setPathEffect(SkDashPathEffect::Make(intervals, 2, 2.5f));
        for (auto degrees : { 270, 360, 540, 720 } ) {
            canvas->drawArc(oval, 0, degrees, false, paint);
            canvas->translate(64, 0);
        }
    }
##

#SeeAlso SkPath::arcTo drawCircle drawOval drawPath

##

# ------------------------------------------------------------------------------

#Method void drawRoundRect(const SkRect& rect, SkScalar rx, SkScalar ry, const SkPaint& paint)
#In Draw
#Line # draws Round_Rect using Clip, Matrix, and Paint ##
#Populate

#Example
#Description
    Top row has a zero radius a generates a rectangle.
    Second row radii sum to less than sides.
    Third row radii sum equals sides.
    Fourth row radii sum exceeds sides; radii are scaled to fit.
##
    void draw(SkCanvas* canvas) {
        SkVector radii[] = { {0, 20}, {10, 10}, {10, 20}, {10, 40} };
        SkPaint paint;
        paint.setStrokeWidth(15);
        paint.setStrokeJoin(SkPaint::kRound_Join);
        paint.setAntiAlias(true);
        for (auto style : { SkPaint::kStroke_Style, SkPaint::kFill_Style  } ) {
            paint.setStyle(style );
            for (size_t i = 0; i < SK_ARRAY_COUNT(radii); ++i) {
               canvas->drawRoundRect({10, 10, 60, 40}, radii[i].fX, radii[i].fY, paint);
               canvas->translate(0, 60);
            }
            canvas->translate(80, -240);
        }
    }
##

#SeeAlso drawRRect drawRect drawDRRect drawPath drawCircle drawOval drawPoint

##

# ------------------------------------------------------------------------------

#Method void drawPath(const SkPath& path, const SkPaint& paint)
#In Draw
#Line # draws Path using Clip, Matrix, and Paint ##
#Populate

#Example
#Description
    Top rows draw stroked path with combinations of joins and caps. The open contour
    is affected by caps; the closed contour is affected by joins.
    Bottom row draws fill the same for open and closed contour.
    First bottom column shows winding fills overlap.
    Second bottom column shows even odd fills exclude overlap.
    Third bottom column shows inverse winding fills area outside both contours.
##
void draw(SkCanvas* canvas) {
    SkPath path;
    path.moveTo(20, 20);
    path.quadTo(60, 20, 60, 60);
    path.close();
    path.moveTo(60, 20);
    path.quadTo(60, 60, 20, 60);
    SkPaint paint;
    paint.setStrokeWidth(10);
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStroke_Style);
    for (auto join: { SkPaint::kBevel_Join, SkPaint::kRound_Join, SkPaint::kMiter_Join } ) {
        paint.setStrokeJoin(join);
        for (auto cap: { SkPaint::kButt_Cap, SkPaint::kSquare_Cap, SkPaint::kRound_Cap  } ) {
            paint.setStrokeCap(cap);
            canvas->drawPath(path, paint);
            canvas->translate(80, 0);
        }
        canvas->translate(-240, 60);
    }
    paint.setStyle(SkPaint::kFill_Style);
    for (auto fill : { SkPath::kWinding_FillType,
                       SkPath::kEvenOdd_FillType,
                       SkPath::kInverseWinding_FillType } ) {
        path.setFillType(fill);
        canvas->save();
        canvas->clipRect({0, 10, 80, 70});
        canvas->drawPath(path, paint);
        canvas->restore();
        canvas->translate(80, 0);
    }
}
##

#SeeAlso SkPath drawLine drawArc drawRect drawPoints

##

# ------------------------------------------------------------------------------
#Subtopic Draw_Image
#Line # draws Image to Canvas ##

drawImage, drawImageRect, and drawImageNine can be called with a bare pointer or
a smart pointer as a convenience. The pairs of calls are otherwise identical.

#Method void drawImage(const SkImage* image, SkScalar left, SkScalar top, const SkPaint* paint = nullptr)
#In Draw_Image
#In Draw
#Line # draws Image at (x, y) position ##
#Populate

#Example
#Height 64
#Image 4
void draw(SkCanvas* canvas) {
   // sk_sp<SkImage> image;
   SkImage* imagePtr = image.get();
   canvas->drawImage(imagePtr, 0, 0);
   SkPaint paint;
   canvas->drawImage(imagePtr, 80, 0, &paint);
   paint.setAlpha(0x80);
   canvas->drawImage(imagePtr, 160, 0, &paint);
}
##

#SeeAlso drawBitmap drawImageLattice drawImageNine drawImageRect SkPaint::setImageFilter

##

# ------------------------------------------------------------------------------

#Method void drawImage(const sk_sp<SkImage>& image, SkScalar left, SkScalar top,
                   const SkPaint* paint = nullptr)
#Populate

#Example
#Height 64
#Image 4
void draw(SkCanvas* canvas) {
   // sk_sp<SkImage> image;
   canvas->drawImage(image, 0, 0);
   SkPaint paint;
   canvas->drawImage(image, 80, 0, &paint);
   paint.setAlpha(0x80);
   canvas->drawImage(image, 160, 0, &paint);
}
##

#SeeAlso drawBitmap drawImageLattice drawImageNine drawImageRect SkPaint::setImageFilter

##

# ------------------------------------------------------------------------------

#Enum SrcRectConstraint
#Line # sets drawImageRect options ##

#Code
#Populate
##

SrcRectConstraint controls the behavior at the edge of source Rect,
provided to drawImageRect, trading off speed for precision.

Image_Filter in Paint may sample multiple pixels in the image. Source Rect
restricts the bounds of pixels that may be read. Image_Filter may slow down if
it cannot read outside the bounds, when sampling near the edge of source Rect.
SrcRectConstraint specifies whether an Image_Filter is allowed to read pixels
outside source Rect.

#Const kStrict_SrcRectConstraint 0
#Line # sample only inside bounds; slower ##
    Requires Image_Filter to respect source Rect,
    sampling only inside of its bounds, possibly with a performance penalty.
##

#Const kFast_SrcRectConstraint 1
#Line # sample outside bounds; faster ##
    Permits Image_Filter to sample outside of source Rect
    by half the width of Image_Filter, permitting it to run faster but with
    error at the image edges.
##

#Example
#Height 64
#Description
    redBorder contains a black and white checkerboard bordered by red.
    redBorder is drawn scaled by 16 on the left.
    The middle and right bitmaps are filtered checkerboards.
    Drawing the checkerboard with kStrict_SrcRectConstraint shows only a blur of black and white.
    Drawing the checkerboard with kFast_SrcRectConstraint allows red to bleed in the corners.
##
void draw(SkCanvas* canvas) {
    SkBitmap redBorder;
    redBorder.allocPixels(SkImageInfo::MakeN32Premul(4, 4));
    SkCanvas checkRed(redBorder);
    checkRed.clear(SK_ColorRED);
    uint32_t checkers[][2] = { { SK_ColorBLACK, SK_ColorWHITE },
                               { SK_ColorWHITE, SK_ColorBLACK } };
    checkRed.writePixels(
            SkImageInfo::MakeN32Premul(2, 2), (void*) checkers, sizeof(checkers[0]), 1, 1);
    canvas->scale(16, 16);
    canvas->drawBitmap(redBorder, 0, 0, nullptr);
    canvas->resetMatrix();
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(redBorder);
    SkPaint lowPaint;
    lowPaint.setFilterQuality(kLow_SkFilterQuality);
    for (auto constraint : { SkCanvas::kStrict_SrcRectConstraint,
                             SkCanvas::kFast_SrcRectConstraint } ) {
        canvas->translate(80, 0);
        canvas->drawImageRect(image.get(), SkRect::MakeLTRB(1, 1, 3, 3),
                SkRect::MakeLTRB(16, 16, 48, 48), &lowPaint, constraint);
    }
}
##

#SeeAlso drawImageRect drawImage SkPaint::setImageFilter

##

# ------------------------------------------------------------------------------

#Method void drawImageRect(const SkImage* image, const SkRect& src, const SkRect& dst,
                       const SkPaint* paint,
                       SrcRectConstraint constraint = kStrict_SrcRectConstraint)
#In Draw_Image
#In Draw
#Line # draws Image, source Rect to destination Rect ##
#Populate

#Example
#Height 64
#Description
    The left bitmap draws with Paint default kNone_SkFilterQuality, and stays within
    its bounds; there is no bleeding with kFast_SrcRectConstraint.
    the middle and right bitmaps draw with kLow_SkFilterQuality; with
    kStrict_SrcRectConstraint, the filter remains within the checkerboard, and
    with kFast_SrcRectConstraint red bleeds on the edges.
##
void draw(SkCanvas* canvas) {
    uint32_t pixels[][4] = {
            { 0xFFFF0000, 0xFFFF0000, 0xFFFF0000, 0xFFFF0000 },
            { 0xFFFF0000, 0xFF000000, 0xFFFFFFFF, 0xFFFF0000 },
            { 0xFFFF0000, 0xFFFFFFFF, 0xFF000000, 0xFFFF0000 },
            { 0xFFFF0000, 0xFFFF0000, 0xFFFF0000, 0xFFFF0000 } };
    SkBitmap redBorder;
    redBorder.installPixels(SkImageInfo::MakeN32Premul(4, 4),
            (void*) pixels, sizeof(pixels[0]));
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(redBorder);
    SkPaint lowPaint;
    for (auto constraint : {
            SkCanvas::kFast_SrcRectConstraint,
            SkCanvas::kStrict_SrcRectConstraint,
            SkCanvas::kFast_SrcRectConstraint } ) {
        canvas->drawImageRect(image.get(), SkRect::MakeLTRB(1, 1, 3, 3),
                SkRect::MakeLTRB(16, 16, 48, 48), &lowPaint, constraint);
        lowPaint.setFilterQuality(kLow_SkFilterQuality);
        canvas->translate(80, 0);
    }
}
##

#SeeAlso SrcRectConstraint drawImage drawImageLattice drawImageNine

##

# ------------------------------------------------------------------------------

#Method void drawImageRect(const SkImage* image, const SkIRect& isrc, const SkRect& dst,
                       const SkPaint* paint, SrcRectConstraint constraint = kStrict_SrcRectConstraint)
#In Draw_Image
#In Draw
#Populate

#Example
#Image 4
void draw(SkCanvas* canvas) {
    // sk_sp<SkImage> image;
    for (auto i : { 1, 2, 4, 8 } ) {
        canvas->drawImageRect(image.get(), SkIRect::MakeLTRB(0, 0, 100, 100),
                SkRect::MakeXYWH(i * 20, i * 20, i * 20, i * 20), nullptr);
    }
}
##

#SeeAlso SrcRectConstraint drawImage drawImageLattice drawImageNine

##

# ------------------------------------------------------------------------------

#Method void drawImageRect(const SkImage* image, const SkRect& dst, const SkPaint* paint)
#In Draw_Image
#In Draw
#Populate

#Example
#Image 4
void draw(SkCanvas* canvas) {
    // sk_sp<SkImage> image;
    for (auto i : { 20, 40, 80, 160 } ) {
        canvas->drawImageRect(image.get(), SkRect::MakeXYWH(i, i, i, i), nullptr);
    }
}
##

#SeeAlso SrcRectConstraint drawImage drawImageLattice drawImageNine

##

# ------------------------------------------------------------------------------

#Method void drawImageRect(const sk_sp<SkImage>& image, const SkRect& src, const SkRect& dst,
                       const SkPaint* paint,
                       SrcRectConstraint constraint = kStrict_SrcRectConstraint)
#In Draw_Image
#In Draw
#Populate

#Example
#Height 64
#Description
    Canvas scales and translates; transformation from src to dst also scales.
    The two matrices are concatenated to create the final transformation.
##
void draw(SkCanvas* canvas) {
    uint32_t pixels[][2] = { { SK_ColorBLACK, SK_ColorWHITE },
                             { SK_ColorWHITE, SK_ColorBLACK } };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeN32Premul(2, 2),
            (void*) pixels, sizeof(pixels[0]));
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(bitmap);
    SkPaint paint;
    canvas->scale(4, 4);
    for (auto alpha : { 50, 100, 150, 255 } ) {
        paint.setAlpha(alpha);
        canvas->drawImageRect(image, SkRect::MakeWH(2, 2), SkRect::MakeWH(8, 8), &paint);
        canvas->translate(8, 0);
    }
}
##

#SeeAlso SrcRectConstraint drawImage drawImageLattice drawImageNine

##

# ------------------------------------------------------------------------------

#Method void drawImageRect(const sk_sp<SkImage>& image, const SkIRect& isrc, const SkRect& dst,
                       const SkPaint* paint, SrcRectConstraint constraint = kStrict_SrcRectConstraint)
#In Draw_Image
#In Draw
#Populate

#Example
#Height 64
void draw(SkCanvas* canvas) {
    uint32_t pixels[][2] = { { 0x00000000, 0x55555555},
                             { 0xAAAAAAAA, 0xFFFFFFFF} };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeN32Premul(2, 2),
            (void*) pixels, sizeof(pixels[0]));
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(bitmap);
    SkPaint paint;
    canvas->scale(4, 4);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, SK_ColorGREEN } ) {
        paint.setColorFilter(SkColorFilter::MakeModeFilter(color, SkBlendMode::kPlus));
        canvas->drawImageRect(image, SkIRect::MakeWH(2, 2), SkRect::MakeWH(8, 8), &paint);
        canvas->translate(8, 0);
    }
}
##

#SeeAlso SrcRectConstraint drawImage drawImageLattice drawImageNine

##

# ------------------------------------------------------------------------------

#Method void drawImageRect(const sk_sp<SkImage>& image, const SkRect& dst, const SkPaint* paint)
#In Draw_Image
#In Draw
#Populate

#Example
#Height 64
void draw(SkCanvas* canvas) {
    uint32_t pixels[][2] = { { 0x00000000, 0x55550000},
                             { 0xAAAA0000, 0xFFFF0000} };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeN32Premul(2, 2),
            (void*) pixels, sizeof(pixels[0]));
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(bitmap);
    SkPaint paint;
    canvas->scale(4, 4);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, SK_ColorGREEN } ) {
        paint.setColorFilter(SkColorFilter::MakeModeFilter(color, SkBlendMode::kPlus));
        canvas->drawImageRect(image, SkRect::MakeWH(8, 8), &paint);
        canvas->translate(8, 0);
    }
}
##

#SeeAlso SrcRectConstraint drawImage drawImageLattice drawImageNine

##

# ------------------------------------------------------------------------------

#Method void drawImageNine(const SkImage* image, const SkIRect& center, const SkRect& dst,
                       const SkPaint* paint = nullptr)
#In Draw_Image
#In Draw
#Line # draws Nine_Patch Image ##

Draws Image image stretched proportionally to fit into Rect dst.
IRect center divides the image into nine sections: four sides, four corners, and
the center. Corners are unmodified or scaled down proportionately if their sides
are larger than dst; center and four sides are scaled to fit remaining space, if any.

Additionally transform draw using Clip, Matrix, and optional Paint paint.

#paint_as_used_by_draw_lattice_or_draw_nine(image)#

If generated mask extends beyond image bounds, replicate image edge colors, just
as Shader made from SkImage::makeShader with SkShader::kClamp_TileMode set
replicates the image edge color when it samples outside of its bounds.

#Param  image      Image containing pixels, dimensions, and format ##
#Param  center     IRect edge of image corners and sides ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint      Paint containing Blend_Mode, Color_Filter, Image_Filter,
                   and so on; or nullptr
##

#Example
#Height 128
#Description
    The leftmost image is smaller than center; only corners are drawn, all scaled to fit.
    The second image equals the size of center; only corners are drawn without scaling.
    The remaining images are larger than center. All corners draw without scaling.
    The sides and center are scaled if needed to take up the remaining space.
##
void draw(SkCanvas* canvas) {
    SkIRect center = { 20, 10, 50, 40 };
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(60, 60));
    SkCanvas bitCanvas(bitmap);
    SkPaint paint;
    SkColor gray = 0xFF000000;
    int left = 0;
    for (auto right: { center.fLeft, center.fRight, bitmap.width() } ) {
        int top = 0;
        for (auto bottom: { center.fTop, center.fBottom, bitmap.height() } ) {
            paint.setColor(gray);
            bitCanvas.drawIRect(SkIRect::MakeLTRB(left, top, right, bottom), paint);
            gray += 0x001f1f1f;
            top = bottom;
        }
        left = right;
    }
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(bitmap);
    SkImage* imagePtr = image.get();
    for (auto dest: { 20, 30, 40, 60, 90 } ) {
        canvas->drawImageNine(imagePtr, center, SkRect::MakeWH(dest, dest), nullptr);
        canvas->translate(dest + 4, 0);
    }
}
##

#SeeAlso drawImage drawBitmapNine drawImageLattice drawImageRect

##

# ------------------------------------------------------------------------------

#Method void drawImageNine(const sk_sp<SkImage>& image, const SkIRect& center, const SkRect& dst,
                       const SkPaint* paint = nullptr)
#In Draw_Image
#In Draw
Draws Image image stretched proportionally to fit into Rect dst.
IRect center divides the image into nine sections: four sides, four corners, and
the center. Corners are not scaled, or scaled down proportionately if their sides
are larger than dst; center and four sides are scaled to fit remaining space, if any.

Additionally transform draw using Clip, Matrix, and optional Paint paint.

#paint_as_used_by_draw_lattice_or_draw_nine(image)#

If generated mask extends beyond image bounds, replicate image edge colors, just
as Shader made from SkImage::makeShader with SkShader::kClamp_TileMode set
replicates the image edge color when it samples outside of its bounds.

#Param  image      Image containing pixels, dimensions, and format ##
#Param  center     IRect edge of image corners and sides ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint      Paint containing Blend_Mode, Color_Filter, Image_Filter,
                   and so on; or nullptr
##

#Example
#Height 128
#Description
    The two leftmost images has four corners and sides to the left and right of center.
    The leftmost image scales the width of corners proportionately to fit.
    The third and fourth image corners are not scaled; the sides and center are scaled to
    fill the remaining space.
    The rightmost image has four corners scaled vertically to fit, and uses sides above
    and below center to fill the remaining space.
##
void draw(SkCanvas* canvas) {
    SkIRect center = { 20, 10, 50, 40 };
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(60, 60));
    SkCanvas bitCanvas(bitmap);
    SkPaint paint;
    SkColor gray = 0xFF000000;
    int left = 0;
    for (auto right: { center.fLeft, center.fRight, bitmap.width() } ) {
        int top = 0;
        for (auto bottom: { center.fTop, center.fBottom, bitmap.height() } ) {
            paint.setColor(gray);
            bitCanvas.drawIRect(SkIRect::MakeLTRB(left, top, right, bottom), paint);
            gray += 0x001f1f1f;
            top = bottom;
        }
        left = right;
    }
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(bitmap);
    for (auto dest: { 20, 30, 40, 60, 90 } ) {
        canvas->drawImageNine(image, center, SkRect::MakeWH(dest, 110 - dest), nullptr);
        canvas->translate(dest + 4, 0);
    }
}
##

#SeeAlso drawImage drawBitmapNine drawImageLattice drawImageRect

##

# ------------------------------------------------------------------------------

#Method void drawBitmap(const SkBitmap& bitmap, SkScalar left, SkScalar top,
                    const SkPaint* paint = nullptr)
#In Draw_Image
#In Draw
#Line # draws Bitmap at (x, y) position ##
#Populate

#Example
#Height 64
void draw(SkCanvas* canvas) {
    uint8_t pixels[][8] = { { 0x00, 0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00, 0x00},
                            { 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00},
                            { 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00},
                            { 0xFF, 0xFF, 0x00, 0xFF, 0xFF, 0x00, 0xFF, 0xFF},
                            { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF},
                            { 0x00, 0x00, 0xFF, 0x00, 0x00, 0xFF, 0x00, 0x00},
                            { 0x00, 0xFF, 0x00, 0xFF, 0xFF, 0x00, 0xFF, 0x00},
                            { 0xFF, 0x00, 0xFF, 0x00, 0x00, 0xFF, 0x00, 0xFF} };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeA8(8, 8),
            (void*) pixels, sizeof(pixels[0]));
    SkPaint paint;
    canvas->scale(4, 4);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xFF007F00} ) {
        paint.setColor(color);
        canvas->drawBitmap(bitmap, 0, 0, &paint);
        canvas->translate(12, 0);
    }
}
##

#SeeAlso drawImage drawBitmapLattice drawBitmapNine drawBitmapRect SkBitmap::readPixels SkBitmap::writePixels

##

# ------------------------------------------------------------------------------

#Method void drawBitmapRect(const SkBitmap& bitmap, const SkRect& src, const SkRect& dst,
                        const SkPaint* paint, SrcRectConstraint constraint = kStrict_SrcRectConstraint)
#In Draw_Image
#In Draw
#Line # draws Bitmap, source Rect to destination Rect ##
#Populate

#Example
#Height 64
void draw(SkCanvas* canvas) {
    uint8_t pixels[][8] = { { 0x00, 0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00, 0x00},
                            { 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00},
                            { 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00},
                            { 0xFF, 0xFF, 0x00, 0xFF, 0xFF, 0x00, 0xFF, 0xFF},
                            { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF},
                            { 0x00, 0x00, 0xFF, 0x00, 0x00, 0xFF, 0x00, 0x00},
                            { 0x00, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xFF, 0x00},
                            { 0x00, 0x00, 0xFF, 0x00, 0x00, 0xFF, 0x00, 0x00} };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeA8(8, 8),
            (void*) pixels, sizeof(pixels[0]));
    SkPaint paint;
    paint.setMaskFilter(SkMaskFilter::MakeBlur(kSolid_SkBlurStyle, 6));
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xFF007F00} ) {
        paint.setColor(color);
        canvas->drawBitmapRect(bitmap, SkRect::MakeWH(8, 8), SkRect::MakeWH(32, 32), &paint);
        canvas->translate(48, 0);
    }
}
##

#SeeAlso drawImageRect drawBitmap drawBitmapLattice drawBitmapNine

##

# ------------------------------------------------------------------------------

#Method void drawBitmapRect(const SkBitmap& bitmap, const SkIRect& isrc, const SkRect& dst,
                        const SkPaint* paint, SrcRectConstraint constraint = kStrict_SrcRectConstraint)
#In Draw_Image
#In Draw
#Populate

#Example
#Height 64
void draw(SkCanvas* canvas) {
    uint8_t pixels[][8] = { { 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00},
                            { 0x00, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xFF, 0x00},
                            { 0xFF, 0x00, 0xFF, 0x00, 0xFF, 0x00, 0x00, 0xFF},
                            { 0xFF, 0x00, 0xFF, 0x00, 0xFF, 0x00, 0x00, 0xFF},
                            { 0xFF, 0x00, 0x00, 0x00, 0x00, 0xFF, 0x00, 0xFF},
                            { 0xFF, 0x00, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0xFF},
                            { 0x00, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xFF, 0x00},
                            { 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00} };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeA8(8, 8),
            (void*) pixels, sizeof(pixels[0]));
    SkPaint paint;
    paint.setFilterQuality(kHigh_SkFilterQuality);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xFF007F00, 0xFF7f007f} ) {
        paint.setColor(color);
        canvas->drawBitmapRect(bitmap, SkIRect::MakeWH(8, 8), SkRect::MakeWH(32, 32), &paint);
        canvas->translate(48.25f, 0);
    }
}
##

#SeeAlso drawImageRect drawBitmap drawBitmapLattice drawBitmapNine

##

# ------------------------------------------------------------------------------

#Method void drawBitmapRect(const SkBitmap& bitmap, const SkRect& dst, const SkPaint* paint,
                        SrcRectConstraint constraint = kStrict_SrcRectConstraint)
#In Draw_Image
#In Draw
#Populate

#Example
#Height 64
void draw(SkCanvas* canvas) {
    uint32_t pixels[][2] = { { 0x00000000, 0x55550000},
                             { 0xAAAA0000, 0xFFFF0000} };
    SkBitmap bitmap;
    bitmap.installPixels(SkImageInfo::MakeN32Premul(2, 2),
            (void*) pixels, sizeof(pixels[0]));
    SkPaint paint;
    canvas->scale(4, 4);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, SK_ColorGREEN } ) {
        paint.setColorFilter(SkColorFilter::MakeModeFilter(color, SkBlendMode::kPlus));
        canvas->drawBitmapRect(bitmap, SkRect::MakeWH(8, 8), &paint);
        canvas->translate(8, 0);
    }
}
##

#SeeAlso drawImageRect drawBitmap drawBitmapLattice drawBitmapNine

##

# ------------------------------------------------------------------------------

#PhraseDef paint_as_used_by_draw_lattice_or_draw_nine(bitmap_or_image)
If Paint paint is supplied, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper. If #bitmap_or_image# is kAlpha_8_SkColorType, apply Shader.
If paint contains Mask_Filter, generate mask from #bitmap_or_image# bounds. If paint
Filter_Quality set to kNone_SkFilterQuality, disable pixel filtering. For all
other values of paint Filter_Quality, use kLow_SkFilterQuality to filter pixels.
Any SkMaskFilter on paint is ignored as is paint Anti_Aliasing state.
##

#Method void drawBitmapNine(const SkBitmap& bitmap, const SkIRect& center, const SkRect& dst,
                        const SkPaint* paint = nullptr)
#In Draw_Image
#In Draw
#Line # draws Nine_Patch Bitmap ##

Draws Bitmap bitmap stretched proportionally to fit into Rect dst.
IRect center divides the bitmap into nine sections: four sides, four corners,
and the center. Corners are not scaled, or scaled down proportionately if their
sides are larger than dst; center and four sides are scaled to fit remaining
space, if any.

Additionally transform draw using Clip, Matrix, and optional Paint paint.

#paint_as_used_by_draw_lattice_or_draw_nine(bitmap)#

If generated mask extends beyond bitmap bounds, replicate bitmap edge colors,
just as Shader made from SkShader::MakeBitmapShader with
SkShader::kClamp_TileMode set replicates the bitmap edge color when it samples
outside of its bounds.

#Param  bitmap     Bitmap containing pixels, dimensions, and format ##
#Param  center     IRect edge of image corners and sides ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint    Paint containing Blend_Mode, Color_Filter, Image_Filter,
                 and so on; or nullptr
##

#Example
#Height 128
#Description
    The two leftmost bitmap draws has four corners and sides to the left and right of center.
    The leftmost bitmap draw scales the width of corners proportionately to fit.
    The third and fourth draw corners are not scaled; the sides and center are scaled to
    fill the remaining space.
    The rightmost bitmap draw has four corners scaled vertically to fit, and uses sides above
    and below center to fill the remaining space.
##
void draw(SkCanvas* canvas) {
    SkIRect center = { 20, 10, 50, 40 };
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(60, 60));
    SkCanvas bitCanvas(bitmap);
    SkPaint paint;
    SkColor gray = 0xFF000000;
    int left = 0;
    for (auto right: { center.fLeft, center.fRight, bitmap.width() } ) {
        int top = 0;
        for (auto bottom: { center.fTop, center.fBottom, bitmap.height() } ) {
            paint.setColor(gray);
            bitCanvas.drawIRect(SkIRect::MakeLTRB(left, top, right, bottom), paint);
            gray += 0x001f1f1f;
            top = bottom;
        }
        left = right;
    }
    for (auto dest: { 20, 30, 40, 60, 90 } ) {
        canvas->drawBitmapNine(bitmap, center, SkRect::MakeWH(dest, 110 - dest), nullptr);
        canvas->translate(dest + 4, 0);
    }
}
##

#SeeAlso drawImageNine drawBitmap drawBitmapLattice drawBitmapRect

##

# ------------------------------------------------------------------------------
#Subtopic Lattice
#Line # divides Bitmap or Image into a rectangular grid ##

#Struct Lattice
#Line # divides Bitmap or Image into a rectangular grid ##

#Code
#Populate
##

Lattice divides Bitmap or Image into a rectangular grid.
Grid entries on even columns and even rows are fixed; these entries are
always drawn at their original size if the destination is large enough.
If the destination side is too small to hold the fixed entries, all fixed
entries are proportionately scaled down to fit.
The grid entries not on even columns and rows are scaled to fit the
remaining space, if any.

    #Enum RectType
    #Line # optional setting per rectangular grid entry ##
        #Code
        #Populate
        ##

        Optional setting per rectangular grid entry to make it transparent,
        or to fill the grid entry with a color.

        #Const kDefault 0
        #Line # draws Bitmap into lattice rectangle ##
        ##

        #Const kTransparent 1
        #Line # skips lattice rectangle by making it transparent ##
        ##

        #Const kFixedColor 2
        #Line # draws one of fColors into lattice rectangle ##
        ##
    ##

#Subtopic Members
##

    #Member const int*   fXDivs
    #Line # x-axis values dividing bitmap ##
        Array of x-axis values that divide the bitmap vertically.
        Array entries must be unique, increasing, greater than or equal to
        fBounds left edge, and less than fBounds right edge.
        Set the first element to fBounds left to collapse the left column of
        fixed grid entries.
    ##

    #Member const int*   fYDivs
    #Line # y-axis values dividing bitmap ##
        Array of y-axis values that divide the bitmap horizontally.
        Array entries must be unique, increasing, greater than or equal to
        fBounds top edge, and less than fBounds bottom edge.
        Set the first element to fBounds top to collapse the top row of fixed
        grid entries.
    ##

    #Member const RectType* fRectTypes
    #Line # array of fill types ##
        Optional array of fill types, one per rectangular grid entry:
        array length must be #Formula # (fXCount + 1) * (fYCount + 1) ##.

        Each RectType is one of: kDefault, kTransparent, kFixedColor.

        Array entries correspond to the rectangular grid entries, ascending
        left to right and then top to bottom.
    ##

    #Member int   fXCount
    #Line # number of x-coordinates ##
        Number of entries in fXDivs array; one less than the number of
        horizontal divisions.
    ##

    #Member int   fYCount
    #Line # number of y-coordinates ##
        Number of entries in fYDivs array; one less than the number of vertical
        divisions.
    ##

    #Member const SkIRect*   fBounds
    #Line # source bounds to draw from ##
       Optional subset IRect source to draw from.
       If nullptr, source bounds is dimensions of Bitmap or Image.
    ##

    #Member const SkColor*   fColors
    #Line # array of colors ##
       Optional array of colors, one per rectangular grid entry.
       Array length must be #Formula # (fXCount + 1) * (fYCount + 1) ##.

       Array entries correspond to the rectangular grid entries, ascending
       left to right, then top to bottom.
    ##

#Struct Lattice ##

#Method void drawBitmapLattice(const SkBitmap& bitmap, const Lattice& lattice, const SkRect& dst,
                           const SkPaint* paint = nullptr)
#In Draw_Image
#In Draw
#Line # draws proportionally stretched Bitmap ##

Draws Bitmap bitmap stretched proportionally to fit into Rect dst.

Lattice lattice divides bitmap into a rectangular grid.
Each intersection of an even-numbered row and column is fixed; like the corners
of drawBitmapNine, fixed lattice elements never scale larger than their initial
size and shrink proportionately when all fixed elements exceed the bitmap
dimension. All other grid elements scale to fill the available space, if any.

Additionally transform draw using Clip, Matrix, and optional Paint paint.

#paint_as_used_by_draw_lattice_or_draw_nine(bitmap)#

If generated mask extends beyond bitmap bounds, replicate bitmap edge colors,
just as Shader made from SkShader::MakeBitmapShader with
SkShader::kClamp_TileMode set replicates the bitmap edge color when it samples
outside of its bounds.

#Param  bitmap     Bitmap containing pixels, dimensions, and format ##
#Param  lattice    division of bitmap into fixed and variable rectangles ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint    Paint containing Blend_Mode, Color_Filter, Image_Filter,
                 and so on; or nullptr
##

#Example
#Height 128
#Description
    The two leftmost bitmap draws has four corners and sides to the left and right of center.
    The leftmost bitmap draw scales the width of corners proportionately to fit.
    The third and fourth draw corners are not scaled; the sides are scaled to
    fill the remaining space; the center is transparent.
    The rightmost bitmap draw has four corners scaled vertically to fit, and uses sides above
    and below center to fill the remaining space.
##
void draw(SkCanvas* canvas) {
    SkIRect center = { 20, 10, 50, 40 };
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(60, 60));
    SkCanvas bitCanvas(bitmap);
    SkPaint paint;
    SkColor gray = 0xFF000000;
    int left = 0;
    for (auto right: { center.fLeft, center.fRight, bitmap.width() } ) {
        int top = 0;
        for (auto bottom: { center.fTop, center.fBottom, bitmap.height() } ) {
            paint.setColor(gray);
            bitCanvas.drawIRect(SkIRect::MakeLTRB(left, top, right, bottom), paint);
            gray += 0x001f1f1f;
            top = bottom;
        }
        left = right;
    }
    const int xDivs[] = { center.fLeft, center.fRight };
    const int yDivs[] = { center.fTop, center.fBottom };
    SkCanvas::Lattice::RectType fillTypes[3][3];
    memset(fillTypes, 0, sizeof(fillTypes));
    fillTypes[1][1] = SkCanvas::Lattice::kTransparent;
    SkColor dummy[9];  // temporary pending bug fix
    SkCanvas::Lattice lattice = { xDivs, yDivs, fillTypes[0], SK_ARRAY_COUNT(xDivs),
         SK_ARRAY_COUNT(yDivs), nullptr, dummy };
    for (auto dest: { 20, 30, 40, 60, 90 } ) {
        canvas->drawBitmapLattice(bitmap, lattice, SkRect::MakeWH(dest, 110 - dest), nullptr);
        canvas->translate(dest + 4, 0);
    }
}
##

#SeeAlso drawImageLattice drawBitmap drawBitmapNine Lattice

##

# ------------------------------------------------------------------------------

#Method void drawImageLattice(const SkImage* image, const Lattice& lattice, const SkRect& dst,
                          const SkPaint* paint = nullptr)
#In Draw_Image
#In Draw
#Line # draws proportionally stretched Image ##

Draws Image image stretched proportionally to fit into Rect dst.

Lattice lattice divides image into a rectangular grid.
Each intersection of an even-numbered row and column is fixed; like the corners
of drawBitmapNine, fixed lattice elements never scale larger than their initial
size and shrink proportionately when all fixed elements exceed the bitmap
dimension. All other grid elements scale to fill the available space, if any.

Additionally transform draw using Clip, Matrix, and optional Paint paint.

#paint_as_used_by_draw_lattice_or_draw_nine(image)#

If generated mask extends beyond bitmap bounds, replicate bitmap edge colors,
just as Shader made from SkShader::MakeBitmapShader with
SkShader::kClamp_TileMode set replicates the bitmap edge color when it samples
outside of its bounds.

#Param  image      Image containing pixels, dimensions, and format ##
#Param  lattice    division of bitmap into fixed and variable rectangles ##
#Param  dst        destination Rect of image to draw to ##
#Param  paint    Paint containing Blend_Mode, Color_Filter, Image_Filter,
                 and so on; or nullptr
##

#Example
#Height 128
#Description
    The leftmost image is smaller than center; only corners are drawn, all scaled to fit.
    The second image equals the size of center; only corners are drawn without scaling.
    The remaining images are larger than center. All corners draw without scaling. The sides
    are scaled if needed to take up the remaining space; the center is transparent.
##
void draw(SkCanvas* canvas) {
    SkIRect center = { 20, 10, 50, 40 };
    SkBitmap bitmap;
    bitmap.allocPixels(SkImageInfo::MakeN32Premul(60, 60));
    SkCanvas bitCanvas(bitmap);
    SkPaint paint;
    SkColor gray = 0xFF000000;
    int left = 0;
    for (auto right: { center.fLeft, center.fRight, bitmap.width() } ) {
        int top = 0;
        for (auto bottom: { center.fTop, center.fBottom, bitmap.height() } ) {
            paint.setColor(gray);
            bitCanvas.drawIRect(SkIRect::MakeLTRB(left, top, right, bottom), paint);
            gray += 0x001f1f1f;
            top = bottom;
        }
        left = right;
    }
    sk_sp<SkImage> image = SkImage::MakeFromBitmap(bitmap);
    SkImage* imagePtr = image.get();
    for (auto dest: { 20, 30, 40, 60, 90 } ) {
        canvas->drawImageNine(imagePtr, center, SkRect::MakeWH(dest, dest), nullptr);
        canvas->translate(dest + 4, 0);
    }
}
##

#SeeAlso drawBitmapLattice drawImage drawImageNine Lattice

##

#Subtopic Lattice ##

#Subtopic Draw_Image ##

# ------------------------------------------------------------------------------
#Subtopic Draw_Text
#Line # draws text into Canvas ##
##

#Method void drawSimpleText(const void* text, size_t byteLength, SkTextEncoding encoding,
                            SkScalar x, SkScalar y, const SkFont& font, const SkPaint& paint)
#In Draw_Text
#In Draw
#Line # draws text at (x, y), using font advance ##
#Populate

#Example
#Height 200
#Description
The same text is drawn varying Paint_Text_Size and varying
Matrix.
##
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkFont font;
    float textSizes[] = { 12, 18, 24, 36 };
    for (auto size: textSizes ) {
        font.setSize(size);
        canvas->drawSimpleText("Aa", 2, kUTF8_SkTextEncoding, 10, 20, font, paint);
        canvas->translate(0, size * 2);
    }
    font.setSize(12);
    float yPos = 20;
    for (auto size: textSizes ) {
        float scale = size / 12.f;
        canvas->resetMatrix();
        canvas->translate(100, 0);
        canvas->scale(scale, scale);
        canvas->drawSimpleText("Aa", 2, kUTF8_SkTextEncoding,
                               10 / scale, yPos / scale, font, paint);
        yPos += size * 2;
    }
}
##

#SeeAlso drawString drawTextBlob

##

# ------------------------------------------------------------------------------

#Method void drawTextBlob(const SkTextBlob* blob, SkScalar x, SkScalar y, const SkPaint& paint)
#In Draw_Text
#In Draw
#Line # draws text with arrays of positions and Paint ##
Draws Text_Blob blob at (x, y), using Clip, Matrix, and Paint paint.

blob contains Glyphs, their positions, and paint attributes specific to text:
#font_metrics#.

Paint_Text_Encoding must be set to kGlyphID_SkTextEncoding.

Elements of paint: Anti_Alias, Blend_Mode, Color including Color_Alpha,
Color_Filter, Paint_Dither, Draw_Looper, Mask_Filter, Path_Effect, Shader, and
Paint_Style; apply to blob. If Paint contains SkPaint::kStroke_Style:
Paint_Miter_Limit, Paint_Stroke_Cap, Paint_Stroke_Join, and Paint_Stroke_Width;
apply to Path created from blob.

#Param  blob     Glyphs, positions, and their paints' text size, typeface, and so on ##
#Param  x        horizontal offset applied to blob ##
#Param  y        vertical offset applied to blob ##
#Param  paint    blend, color, stroking, and so on, used to draw ##

#Example
#Height 120
void draw(SkCanvas* canvas) {
    SkTextBlobBuilder textBlobBuilder;
    const char bunny[] = "/(^x^)\\";
    const int len = sizeof(bunny) - 1;
    uint16_t glyphs[len];
    SkFont font;
    font.textToGlyphs(bunny, len, SkTextEncoding::kUTF8, glyphs, len);
    int runs[] = { 3, 1, 3 };
    SkPoint textPos = { 20, 100 };
    int glyphIndex = 0;
    for (auto runLen : runs) {
        font.setSize(1 == runLen ? 20 : 50);
        const SkTextBlobBuilder::RunBuffer& run =
                textBlobBuilder.allocRun(font, runLen, textPos.fX, textPos.fY);
        memcpy(run.glyphs, &glyphs[glyphIndex], sizeof(glyphs[0]) * runLen);
        font.setSize(1 == runLen ? 20 : 50);
        textPos.fX += font.measureText(&glyphs[glyphIndex], sizeof(glyphs[0]) * runLen,
                SkTextEncoding::kGlyphID);
        glyphIndex += runLen;
    }
    sk_sp<const SkTextBlob> blob = textBlobBuilder.make();
    canvas->drawTextBlob(blob.get(), 0, 0, SkPaint());
}
##

#SeeAlso drawText

##

# ------------------------------------------------------------------------------

#Method void drawTextBlob(const sk_sp<SkTextBlob>& blob, SkScalar x, SkScalar y, const SkPaint& paint)

Draws Text_Blob blob at (x, y), using Clip, Matrix, and Paint paint.

blob contains Glyphs, their positions, and paint attributes specific to text:
#font_metrics#.

Paint_Text_Encoding must be set to kGlyphID_SkTextEncoding.

Elements of paint: Path_Effect, Mask_Filter, Shader, Color_Filter,
Image_Filter, and Draw_Looper; apply to blob.

#Param  blob     Glyphs, positions, and their paints' text size, typeface, and so on ##
#Param  x        horizontal offset applied to blob ##
#Param  y        vertical offset applied to blob ##
#Param  paint    blend, color, stroking, and so on, used to draw ##

#Example
#Height 120
#Description
Paint attributes related to text, like text size, have no effect on paint passed to drawTextBlob.
##
    void draw(SkCanvas* canvas) {
        SkTextBlobBuilder textBlobBuilder;
        SkFont font;
        font.setSize(50);
        const SkTextBlobBuilder::RunBuffer& run =
                textBlobBuilder.allocRun(font, 1, 20, 100);
        run.glyphs[0] = 20;
        sk_sp<const SkTextBlob> blob = textBlobBuilder.make();
        SkPaint paint;
        paint.setTextSize(10);
        paint.setColor(SK_ColorBLUE);
        canvas->drawTextBlob(blob.get(), 0, 0, paint);
    }
##

#SeeAlso drawText

##

# ------------------------------------------------------------------------------

#Method void drawPicture(const SkPicture* picture)
#In Draw
#Line # draws Picture using Clip and Matrix ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkPictureRecorder recorder;
    SkCanvas* recordingCanvas = recorder.beginRecording(50, 50);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xff007f00 } ) {
        SkPaint paint;
        paint.setColor(color);
        recordingCanvas->drawRect({10, 10, 30, 40}, paint);
        recordingCanvas->translate(10, 10);
        recordingCanvas->scale(1.2f, 1.4f);
    }
    sk_sp<SkPicture> playback = recorder.finishRecordingAsPicture();
    canvas->drawPicture(playback);
    canvas->scale(2, 2);
    canvas->translate(50, 0);
    canvas->drawPicture(playback);
}
##

#SeeAlso drawDrawable SkPicture SkPicture::playback

##

# ------------------------------------------------------------------------------

#Method void drawPicture(const sk_sp<SkPicture>& picture)
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkPictureRecorder recorder;
    SkCanvas* recordingCanvas = recorder.beginRecording(50, 50);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xff007f00 } ) {
        SkPaint paint;
        paint.setColor(color);
        recordingCanvas->drawRect({10, 10, 30, 40}, paint);
        recordingCanvas->translate(10, 10);
        recordingCanvas->scale(1.2f, 1.4f);
    }
    sk_sp<SkPicture> playback = recorder.finishRecordingAsPicture();
    canvas->drawPicture(playback);
    canvas->scale(2, 2);
    canvas->translate(50, 0);
    canvas->drawPicture(playback);
}
##

#SeeAlso drawDrawable SkPicture SkPicture::playback

##

# ------------------------------------------------------------------------------

#Method void drawPicture(const SkPicture* picture, const SkMatrix* matrix, const SkPaint* paint)
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkPictureRecorder recorder;
    SkCanvas* recordingCanvas = recorder.beginRecording(50, 50);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xff007f00 } ) {
        paint.setColor(color);
        recordingCanvas->drawRect({10, 10, 30, 40}, paint);
        recordingCanvas->translate(10, 10);
        recordingCanvas->scale(1.2f, 1.4f);
    }
    sk_sp<SkPicture> playback = recorder.finishRecordingAsPicture();
    const SkPicture* playbackPtr = playback.get();
    SkMatrix matrix;
    matrix.reset();
    for (auto alpha : { 70, 140, 210 } ) {
    paint.setAlpha(alpha);
    canvas->drawPicture(playbackPtr, &matrix, &paint);
    matrix.preTranslate(70, 70);
    }
}
##

#SeeAlso drawDrawable SkPicture SkPicture::playback

##

# ------------------------------------------------------------------------------

#Method void drawPicture(const sk_sp<SkPicture>& picture, const SkMatrix* matrix, const SkPaint* paint)
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkPictureRecorder recorder;
    SkCanvas* recordingCanvas = recorder.beginRecording(50, 50);
    for (auto color : { SK_ColorRED, SK_ColorBLUE, 0xff007f00 } ) {
        paint.setColor(color);
        recordingCanvas->drawRect({10, 10, 30, 40}, paint);
        recordingCanvas->translate(10, 10);
        recordingCanvas->scale(1.2f, 1.4f);
    }
    sk_sp<SkPicture> playback = recorder.finishRecordingAsPicture();
    SkMatrix matrix;
    matrix.reset();
    for (auto alpha : { 70, 140, 210 } ) {
    paint.setAlpha(alpha);
    canvas->drawPicture(playback, &matrix, &paint);
    matrix.preTranslate(70, 70);
    }
}
##

#SeeAlso drawDrawable SkPicture SkPicture::playback

##

# ------------------------------------------------------------------------------

#Method void drawVertices(const SkVertices* vertices, SkBlendMode mode, const SkPaint& paint)
#In Draw
#Line # draws Vertices, a triangle mesh ##
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkPoint points[] = { { 0, 0 }, { 250, 0 }, { 100, 100 }, { 0, 250 } };
    SkColor colors[] = { SK_ColorRED, SK_ColorBLUE, SK_ColorYELLOW, SK_ColorCYAN };
    auto vertices = SkVertices::MakeCopy(SkVertices::kTriangleFan_VertexMode,
            SK_ARRAY_COUNT(points), points, nullptr, colors);
    canvas->drawVertices(vertices.get(), SkBlendMode::kSrc, paint);
}
##

#SeeAlso drawPatch drawPicture

##

# ------------------------------------------------------------------------------

#Method void drawVertices(const sk_sp<SkVertices>& vertices, SkBlendMode mode, const SkPaint& paint)
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkPoint points[] = { { 0, 0 }, { 250, 0 }, { 100, 100 }, { 0, 250 } };
    SkPoint texs[] = { { 0, 0 }, { 0, 250 }, { 250, 250 }, { 250, 0 } };
    SkColor colors[] = { SK_ColorRED, SK_ColorBLUE, SK_ColorYELLOW, SK_ColorCYAN };
    paint.setShader(SkGradientShader::MakeLinear(points, colors, nullptr, 4,
            SkShader::kClamp_TileMode));
    auto vertices = SkVertices::MakeCopy(SkVertices::kTriangleFan_VertexMode,
            SK_ARRAY_COUNT(points), points, texs, colors);
    canvas->drawVertices(vertices, SkBlendMode::kDarken, paint);
}
##

#SeeAlso drawPatch drawPicture

##

# ------------------------------------------------------------------------------

#Method void drawVertices(const SkVertices* vertices, const SkVertices::Bone bones[],
                          int boneCount, SkBlendMode mode, const SkPaint& paint)
#Populate

#NoExample
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkPoint points[] = { { 0, 0 }, { 250, 0 }, { 100, 100 }, { 0, 250 } };
    SkPoint texs[] = { { 0, 0 }, { 0, 250 }, { 250, 250 }, { 250, 0 } };
    SkColor colors[] = { SK_ColorRED, SK_ColorBLUE, SK_ColorYELLOW, SK_ColorCYAN };
    SkVertices::BoneIndices boneIndices[] = { { 0, 0, 0, 0 },
                                              { 1, 0, 0, 0 },
                                              { 2, 0, 0, 0 },
                                              { 3, 0, 0, 0 } };
    SkVertices::BoneWeights boneWeights[] = { { 0.0f, 0.0f, 0.0f, 0.0f },
                                              { 1.0f, 0.0f, 0.0f, 0.0f },
                                              { 1.0f, 0.0f, 0.0f, 0.0f },
                                              { 1.0f, 0.0f, 0.0f, 0.0f } };
    SkVertices::Bone bones[] = { {{ 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f }},
                                 {{ 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 20.0f }},
                                 {{ 1.0f, 0.0f, 0.0f, 1.0f, 50.0f, 50.0f }},
                                 {{ 1.0f, 0.0f, 0.0f, 1.0f, 20.0f, 0.0f }} };
    paint.setShader(SkGradientShader::MakeLinear(points, colors, nullptr, 4,
            SkShader::kClamp_TileMode));
    auto vertices = SkVertices::MakeCopy(SkVertices::kTriangleFan_VertexMode,
            SK_ARRAY_COUNT(points), points, texs, colors, boneIndices, boneWeights);
    canvas->drawVertices(vertices.get(), bones, SK_ARRAY_COUNT(bones), SkBlendMode::kDarken, paint);
}
##

#SeeAlso drawPatch drawPicture

##

# ------------------------------------------------------------------------------

#Method void drawVertices(const sk_sp<SkVertices>& vertices, const SkVertices::Bone bones[],
                          int boneCount, SkBlendMode mode, const SkPaint& paint)
#Populate

#NoExample
void draw(SkCanvas* canvas) {
    SkPaint paint;
    SkPoint points[] = { { 0, 0 }, { 250, 0 }, { 100, 100 }, { 0, 250 } };
    SkPoint texs[] = { { 0, 0 }, { 0, 250 }, { 250, 250 }, { 250, 0 } };
    SkColor colors[] = { SK_ColorRED, SK_ColorBLUE, SK_ColorYELLOW, SK_ColorCYAN };
    SkVertices::BoneIndices boneIndices[] = { { 0, 0, 0, 0 },
                                              { 1, 0, 0, 0 },
                                              { 2, 0, 0, 0 },
                                              { 3, 0, 0, 0 } };
    SkVertices::BoneWeights boneWeights[] = { { 0.0f, 0.0f, 0.0f, 0.0f },
                                              { 1.0f, 0.0f, 0.0f, 0.0f },
                                              { 1.0f, 0.0f, 0.0f, 0.0f },
                                              { 1.0f, 0.0f, 0.0f, 0.0f } };
    SkVertices::Bone bones[] = { {{ 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f }},
                                 {{ 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 20.0f }},
                                 {{ 1.0f, 0.0f, 0.0f, 1.0f, 50.0f, 50.0f }},
                                 {{ 1.0f, 0.0f, 0.0f, 1.0f, 20.0f, 0.0f }} };
    paint.setShader(SkGradientShader::MakeLinear(points, colors, nullptr, 4,
            SkShader::kClamp_TileMode));
    auto vertices = SkVertices::MakeCopy(SkVertices::kTriangleFan_VertexMode,
            SK_ARRAY_COUNT(points), points, texs, colors, boneIndices, boneWeights);
    canvas->drawVertices(vertices, bones, SK_ARRAY_COUNT(bones), SkBlendMode::kDarken, paint);
}
##

#SeeAlso drawPatch drawPicture

##

# ------------------------------------------------------------------------------

#Method void drawPatch(const SkPoint cubics[12], const SkColor colors[4],
                   const SkPoint texCoords[4], SkBlendMode mode, const SkPaint& paint)
#In Draw
#Line # draws Coons_Patch ##
#Populate

#Example
#Image 5
void draw(SkCanvas* canvas) {
    // SkBitmap source = cmbkygk;
    SkPaint paint;
    paint.setFilterQuality(kLow_SkFilterQuality);
    paint.setAntiAlias(true);
    SkPoint cubics[] = { { 3, 1 },    { 4, 2 }, { 5, 1 },    { 7, 3 },
                      /* { 7, 3 }, */ { 6, 4 }, { 7, 5 },    { 5, 7 },
                      /* { 5, 7 }, */ { 4, 6 }, { 3, 7 },    { 1, 5 },
                      /* { 1, 5 }, */ { 2, 4 }, { 1, 3 }, /* { 3, 1 } */ };
    SkColor colors[] = { 0xbfff0000, 0xbf0000ff, 0xbfff00ff, 0xbf00ffff };
    SkPoint texCoords[] = { { -30, -30 }, { 162, -30}, { 162, 162}, { -30, 162} };
    paint.setShader(SkShader::MakeBitmapShader(source, SkShader::kClamp_TileMode,
                                                       SkShader::kClamp_TileMode, nullptr));
    canvas->scale(15, 15);
    for (auto blend : { SkBlendMode::kSrcOver, SkBlendMode::kModulate, SkBlendMode::kXor } ) {
        canvas->drawPatch(cubics, colors, texCoords, blend, paint);
        canvas->translate(4, 4);
    }
}
##

#ToDo can patch use image filter? ##
#SeeAlso drawVertices drawPicture

##

# ------------------------------------------------------------------------------

#Method void drawPatch(const SkPoint cubics[12], const SkColor colors[4],
                   const SkPoint texCoords[4], const SkPaint& paint)
#Populate

#Example
void draw(SkCanvas* canvas) {
    SkPaint paint;
    paint.setAntiAlias(true);
    SkPoint cubics[] = { { 3, 1 },    { 4, 2 }, { 5, 1 },    { 7, 3 },
                      /* { 7, 3 }, */ { 6, 4 }, { 7, 5 },    { 5, 7 },
                      /* { 5, 7 }, */ { 4, 6 }, { 3, 7 },    { 1, 5 },
                      /* { 1, 5 }, */ { 2, 4 }, { 1, 3 }, /* { 3, 1 } */ };
    SkColor colors[] = { SK_ColorRED, SK_ColorBLUE, SK_ColorYELLOW, SK_ColorCYAN };
    canvas->scale(30, 30);
    canvas->drawPatch(cubics, colors, nullptr, paint);
    SkPoint text[] = { {3,0.9f}, {4,2.5f}, {5,0.9f}, {7.5f,3.2f}, {5.5f,4.2f},
            {7.5f,5.2f}, {5,7.5f}, {4,5.9f}, {3,7.5f}, {0.5f,5.2f}, {2.5f,4.2f},
            {0.5f,3.2f} };

    SkFont font(nullptr, 18.f / 30);
    for (int i = 0; i< 10; ++i) {
       char digit = '0' + i;
       canvas->drawSimpleText(&digit, kUTF8_SkTextEncoding, 1, text[i].fX, text[i].fY, font, paint);
    }
    canvas->drawString("10", text[10].fX, text[10].fY, font, paint);
    canvas->drawString("11", text[11].fX, text[11].fY, font, paint);
    paint.setStyle(SkPaint::kStroke_Style);
    canvas->drawPoints(SkCanvas::kPolygon_PointMode, 12, cubics, paint);
    canvas->drawLine(cubics[11].fX, cubics[11].fY, cubics[0].fX, cubics[0].fY, paint);
}
##

#Example
#Image 6
void draw(SkCanvas* canvas) {
    // SkBitmap source = checkerboard;
    SkPaint paint;
    paint.setFilterQuality(kLow_SkFilterQuality);
    paint.setAntiAlias(true);
    SkPoint cubics[] = { { 3, 1 },    { 4, 2 }, { 5, 1 },    { 7, 3 },
                      /* { 7, 3 }, */ { 6, 4 }, { 7, 5 },    { 5, 7 },
                      /* { 5, 7 }, */ { 4, 6 }, { 3, 7 },    { 1, 5 },
                      /* { 1, 5 }, */ { 2, 4 }, { 1, 3 }, /* { 3, 1 } */ };
    SkPoint texCoords[] = { { 0, 0 }, { 0, 62}, { 62, 62}, { 62, 0 } };
    paint.setShader(SkShader::MakeBitmapShader(source, SkShader::kClamp_TileMode,
                                                       SkShader::kClamp_TileMode, nullptr));
    canvas->scale(30, 30);
    canvas->drawPatch(cubics, nullptr, texCoords, paint);
}
##

#ToDo can patch use image filter? ##
#SeeAlso drawVertices drawPicture

##

# ------------------------------------------------------------------------------

#Method void drawAtlas(const SkImage* atlas, const SkRSXform xform[], const SkRect tex[],
                   const SkColor colors[], int count, SkBlendMode mode, const SkRect* cullRect,
                   const SkPaint* paint)
#In Draw
#Line # draws sprites using Clip, Matrix, and Paint ##
#Populate

#Example
#Image 3
void draw(SkCanvas* canvas) {
  // SkBitmap source = mandrill;
  SkRSXform xforms[] = { { .5f, 0, 0, 0 }, {0, .5f, 200, 100 } };
  SkRect tex[] = { { 0, 0, 250, 250 }, { 0, 0, 250, 250 } };
  SkColor colors[] = { 0x7f55aa00, 0x7f3333bf };
  const SkImage* imagePtr = image.get();
  canvas->drawAtlas(imagePtr, xforms, tex, colors, 2, SkBlendMode::kSrcOver, nullptr, nullptr);
}
##

#SeeAlso drawBitmap drawImage

##

# ------------------------------------------------------------------------------

#Method void drawAtlas(const sk_sp<SkImage>& atlas, const SkRSXform xform[], const SkRect tex[],
                   const SkColor colors[], int count, SkBlendMode mode, const SkRect* cullRect,
                   const SkPaint* paint)
#Populate

#Example
#Image 3
void draw(SkCanvas* canvas) {
  // SkBitmap source = mandrill;
  SkRSXform xforms[] = { { .5f, 0, 0, 0 }, {0, .5f, 200, 100 } };
  SkRect tex[] = { { 0, 0, 250, 250 }, { 0, 0, 250, 250 } };
  SkColor colors[] = { 0x7f55aa00, 0x7f3333bf };
  SkPaint paint;
  paint.setAlpha(127);
  canvas->drawAtlas(image, xforms, tex, colors, 2, SkBlendMode::kPlus, nullptr, &paint);
}
##

#ToDo bug in example on cpu side, gpu looks ok ##

#SeeAlso drawBitmap drawImage

##

# ------------------------------------------------------------------------------

#Method void drawAtlas(const SkImage* atlas, const SkRSXform xform[], const SkRect tex[], int count,
                   const SkRect* cullRect, const SkPaint* paint)
#Populate

#Example
#Image 3
void draw(SkCanvas* canvas) {
  // sk_sp<SkImage> image = mandrill;
  SkRSXform xforms[] = { { .5f, 0, 0, 0 }, {0, .5f, 200, 100 } };
  SkRect tex[] = { { 0, 0, 250, 250 }, { 0, 0, 250, 250 } };
  const SkImage* imagePtr = image.get();
  canvas->drawAtlas(imagePtr, xforms, tex, 2, nullptr, nullptr);
}
##

#SeeAlso drawBitmap drawImage

##

# ------------------------------------------------------------------------------

#Method void drawAtlas(const sk_sp<SkImage>& atlas, const SkRSXform xform[], const SkRect tex[],
                   int count, const SkRect* cullRect, const SkPaint* paint)
#Populate

#Example
#Image 3
void draw(SkCanvas* canvas) {
  // sk_sp<SkImage> image = mandrill;
  SkRSXform xforms[] = { { 1, 0, 0, 0 }, {0, 1, 300, 100 } };
  SkRect tex[] = { { 0, 0, 200, 200 }, { 200, 0, 400, 200 } };
  canvas->drawAtlas(image, xforms, tex, 2, nullptr, nullptr);
}
##

#SeeAlso drawBitmap drawImage

##

# ------------------------------------------------------------------------------

#Method void drawDrawable(SkDrawable* drawable, const SkMatrix* matrix = nullptr)
#In Draw
#Line # draws Drawable, encapsulated drawing commands ##
#Populate

#Example
#Height 100
#Function
struct MyDrawable : public SkDrawable {
    SkRect onGetBounds() override { return SkRect::MakeWH(50, 100);  }

    void onDraw(SkCanvas* canvas) override {
       SkPath path;
       path.conicTo(10, 90, 50, 90, 0.9f);
       SkPaint paint;
       paint.setColor(SK_ColorBLUE);
       canvas->drawRect(path.getBounds(), paint);
       paint.setAntiAlias(true);
       paint.setColor(SK_ColorWHITE);
       canvas->drawPath(path, paint);
    }
};

#Function ##
void draw(SkCanvas* canvas) {
    sk_sp<SkDrawable> drawable(new MyDrawable);
  SkMatrix matrix;
  matrix.setTranslate(10, 10);
  canvas->drawDrawable(drawable.get(), &matrix);
}
##

#SeeAlso SkDrawable drawPicture

##

# ------------------------------------------------------------------------------

#Method void drawDrawable(SkDrawable* drawable, SkScalar x, SkScalar y)
#Populate

#Example
#Height 100
#Function
struct MyDrawable : public SkDrawable {
    SkRect onGetBounds() override { return SkRect::MakeWH(50, 100);  }

    void onDraw(SkCanvas* canvas) override {
       SkPath path;
       path.conicTo(10, 90, 50, 90, 0.9f);
       SkPaint paint;
       paint.setColor(SK_ColorBLUE);
       canvas->drawRect(path.getBounds(), paint);
       paint.setAntiAlias(true);
       paint.setColor(SK_ColorWHITE);
       canvas->drawPath(path, paint);
    }
};

#Function ##
void draw(SkCanvas* canvas) {
    sk_sp<SkDrawable> drawable(new MyDrawable);
  canvas->drawDrawable(drawable.get(), 10, 10);
}
##

#SeeAlso SkDrawable drawPicture

##

# ------------------------------------------------------------------------------

#Method void drawAnnotation(const SkRect& rect, const char key[], SkData* value)
#In Draw
#In Utility
#Line # associates a Rect with a key-value pair ##
#Populate

#Example
    #Height 1
    const char text[] = "Click this link!";
    SkRect bounds;
    SkPaint paint;
    SkFont font(nullptr, 40);
    (void)font.measureText(text, strlen(text), SkTextEncoding::kUTF8, &bounds);
    const char url[] = "https://www.google.com/";
    sk_sp<SkData> urlData(SkData::MakeWithCString(url));
    canvas->drawAnnotation(bounds, "url_key", urlData.get());
##

#SeeAlso SkPicture SkDocument

##

# ------------------------------------------------------------------------------

#Method void drawAnnotation(const SkRect& rect, const char key[], const sk_sp<SkData>& value)
#Populate

#Example
#Height 1
    const char text[] = "Click this link!";
    SkRect bounds;
    SkPaint paint;
    SkFont font(nullptr, 40);
    (void)font.measureText(text, strlen(text), SkTextEncoding::kUTF8, &bounds);
    const char url[] = "https://www.google.com/";
    sk_sp<SkData> urlData(SkData::MakeWithCString(url));
    canvas->drawAnnotation(bounds, "url_key", urlData.get());
##

#SeeAlso SkPicture SkDocument

##

# ------------------------------------------------------------------------------

#Method virtual bool isClipEmpty() const
#In Property
#Line # returns if Clip is empty ##
#Populate

#Example
    void draw(SkCanvas* canvas) {
        SkDebugf("clip is%s empty\n", canvas->isClipEmpty() ? "" : " not");
        SkPath path;
        canvas->clipPath(path);
        SkDebugf("clip is%s empty\n", canvas->isClipEmpty() ? "" : " not");
    }
    #StdOut
        clip is not empty
        clip is empty
    ##
##

#SeeAlso isClipRect getLocalClipBounds getDeviceClipBounds

##

# ------------------------------------------------------------------------------

#Method virtual bool isClipRect() const
#In Property
#Line # returns if Clip is Rect and not empty ##
#Populate

#Example
    void draw(SkCanvas* canvas) {
        SkDebugf("clip is%s rect\n", canvas->isClipRect() ? "" : " not");
        canvas->clipRect({0, 0, 0, 0});
        SkDebugf("clip is%s rect\n", canvas->isClipRect() ? "" : " not");
    }
    #StdOut
        clip is rect
        clip is not rect
    ##
##

#SeeAlso isClipEmpty getLocalClipBounds getDeviceClipBounds

##

#Class SkCanvas ##

#Topic Canvas ##