Cary Clark 186d08f621 fix bugs exposed by documenting SkImageInfo

- More rigorous symbol identification creates additional
links, and finds spurious errors like unnecessary
parentheses.

- Fixed code to allow preprocessor directives in
#Code blocks (still more to do).

- Fixed examples waiting on fiddle updates.

- Make SkImageInfo officially documented (update in status.json).

- Fixed enum indentation.



Docs-Preview: https://skia.org/?cl=115656
Bug: skia:6898
Change-Id: Ifcf5cfd3f6c03b3b83155c898b2b035a2f3d443c
Reviewed-on: https://skia-review.googlesource.com/115656
Commit-Queue: Cary Clark <caryclark@skia.org>
Reviewed-by: Cary Clark <caryclark@skia.org>

2018-04-03 16:09:56 +00:00

363 KiB

Raw Blame History

SkCanvas Reference

Canvas

Overview

Overview Subtopic

name	description
Class or Struct	embedded struct and class members
Constant	enum and enum class, const values
Constructor	functions that construct SkCanvas
Member Function	static functions and member methods
Related Function	similar methods grouped together

Class SkCanvas

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.

name	description
Clip	stack of clipping Paths
Draw	draws into Canvas
Draw Image	draws Image to Canvas
Draw Text	draws text into Canvas
Layer	temporary Bitmap to draw into
Matrix	coordinate transformation
Pixels	read and write pixel values
Property	metrics and attributes
State Stack	stack of state for hierarchical drawing
Utility	rarely called management functions

Constant

name	description
ColorBehavior	Android framework only
PointMode	sets drawPoints options
SrcRectConstraint	sets drawImageRect options
_anonymous	sets SaveLayerRec options

Class or Struct

name	description
Lattice	divides Bitmap or Image into a rectangular grid
SaveLayerRec	contains the state used to create the Layer

Constructor

Create the desired type of Surface to obtain its Canvas when possible. Useful when no Surface is required, and some helpers implicitly create Raster Surface.

name	description
MakeRasterDirect	creates from SkImageInfo and Pixel Storage
MakeRasterDirectN32	creates from image data and Pixel Storage
SkCanvas()	creates with no Surface, no dimensions
SkCanvas(const SkBitmap& bitmap)	uses existing Bitmap
SkCanvas(const SkBitmap& bitmap, ColorBehavior behavior)	Android framework only
SkCanvas(const SkBitmap& bitmap, const SkSurfaceProps& props)	uses existing Bitmap and Surface Properties
SkCanvas(int width, int height, const SkSurfaceProps* props = nullptr)	no Surface, set dimensions, Surface Properties
makeSurface	creates Surface matching SkImageInfo and SkSurfaceProps
~SkCanvas()	draws saved Layers, frees resources

Member Function

name	description
MakeRasterDirect	creates from SkImageInfo and Pixel Storage
MakeRasterDirectN32	creates from image data and Pixel Storage
accessTopLayerPixels	returns writable pixel access if available
accessTopRasterHandle	returns context that tracks Clip and Matrix
androidFramework setDeviceClipRestriction	for use by Android framework
clear	fills Clip with Color
clipPath	combines Clip with Path
clipRRect	combines Clip with Round Rect
clipRect	combines Clip with Rect
clipRegion	combines Clip with Region
concat	multiplies Matrix by Matrix
discard	makes Canvas contents undefined
drawAnnotation	associates a Rect with a key-value pair
drawArc	draws Arc using Clip, Matrix, and Paint
drawAtlas	draws sprites using Clip, Matrix, and Paint
drawBitmap	draws Bitmap at (x, y) position
drawBitmapLattice	draws proportionally stretched Bitmap
drawBitmapNine	draws Nine Patch Bitmap
drawBitmapRect	draws Bitmap, source Rect to destination Rect
drawCircle	draws Circle using Clip, Matrix, and Paint
drawColor	fills Clip with Color and Blend Mode
drawDRRect	draws double Round Rect stroked or filled
drawDrawable	draws Drawable, encapsulated drawing commands
drawIRect	draws IRect using Clip, Matrix, and Paint
drawImage	draws Image at (x, y) position
drawImageLattice	draws proportionally stretched Image
drawImageNine	draws Nine Patch Image
drawImageRect	draws Image, source Rect to destination Rect
drawLine	draws line segment between two points
drawOval	draws Oval using Clip, Matrix, and Paint
drawPaint	fills Clip with Paint
drawPatch	draws Coons_Patch
drawPath	draws Path using Clip, Matrix, and Paint
drawPicture	draws Picture using Clip and Matrix
drawPoint	draws point at (x, y) position
drawPoints	draws array as points, lines, polygon
drawPosText	draws text at array of (x, y) positions
drawPosTextH	draws text at x positions with common baseline
drawRRect	draws Round Rect using Clip, Matrix, and Paint
drawRect	draws Rect using Clip, Matrix, and Paint
drawRegion	draws Region using Clip, Matrix, and Paint
drawRoundRect	draws Round Rect using Clip, Matrix, and Paint
drawString	draws null terminated string at (x, y) using font advance
drawText	draws text at (x, y), using font advance
drawTextBlob	draws text with arrays of positions and Paint
drawTextOnPath	draws text following Path contour
drawTextOnPathHV	draws text following Path with offsets
drawTextRSXform	draws text with array of RSXform
drawVertices	draws Vertices, a triangle mesh
flush	triggers execution of all pending draw operations
getBaseLayerSize	returns size of base Layer in global coordinates
getDeviceClipBounds	returns IRect bounds of Clip
getGrContext	returns GPU Context of the GPU Surface
getLocalClipBounds	returns Clip bounds in source coordinates
getMetaData	associates additional data with the canvas
getProps	copies Surface Properties if available
getSaveCount	returns depth of stack containing Clip and Matrix
getTotalMatrix	returns Matrix
imageInfo	returns Image Info for Canvas
isClipEmpty	returns if Clip is empty
isClipRect	returns if Clip is Rect and not empty
makeSurface	creates Surface matching SkImageInfo and SkSurfaceProps
peekPixels	returns if Canvas has direct access to its pixels
quickReject	returns if Rect is outside Clip
readPixels	copies and converts rectangle of pixels from Canvas
resetMatrix	resets Matrix to identity
restore	restores changes to Clip and Matrix, pops save stack
restoreToCount	restores changes to Clip and Matrix to given depth
rotate	rotates Matrix
save	saves Clip and Matrix on stack
saveLayer	saves Clip and Matrix on stack; creates Layer
saveLayerAlpha	saves Clip and Matrix on stack; creates Layer; sets opacity
saveLayerPreserveLCDTextRequests	saves Clip and Matrix on stack; creates Layer for LCD text
scale	scales Matrix
setAllowSimplifyClip	experimental
setMatrix	sets Matrix
skew	skews Matrix
translate	translates Matrix
writePixels	copies and converts rectangle of pixels to Canvas

MakeRasterDirect

static std::unique_ptr<SkCanvas> MakeRasterDirect(const SkImageInfo& info, void* pixels,
                                                  size_t rowBytes,
                                                  const SkSurfaceProps* props = nullptr)

Allocates raster Canvas that will draw directly into pixels.

Canvas is returned if all parameters are valid. Valid parameters include: info dimensions are zero or positive; info contains Color Type and Alpha Type supported by Raster Surface; pixels is not nullptr; rowBytes is zero or large enough to contain info width pixels of Color Type.

Pass zero for rowBytes to compute rowBytes from info width and size of pixel. If rowBytes is greater than zero, it must be equal to or greater than info width times bytes required for Color Type.

Pixel buffer size should be info height times computed rowBytes. Pixels are not initialized. To access pixels after drawing, call flush or peekPixels.

Parameters

`info`	width, height, Color Type, Alpha Type, Color Space, of Raster Surface; width, or height, or both, may be zero
`pixels`	pointer to destination pixels buffer
`rowBytes`	interval from one Surface row to the next, or zero
`props`	LCD striping orientation and setting for device independent fonts; may be nullptr

Return Value

Canvas if all parameters are valid; otherwise, nullptr

Example

Allocates a three by three bitmap, clears it to white, and draws a black pixel in the center.

Example Output

---
-x-
---

MakeRasterDirectN32

static std::unique_ptr<SkCanvas> MakeRasterDirectN32(int width, int height, SkPMColor* pixels,
                                                     size_t rowBytes)

Allocates raster Canvas specified by inline image specification. Subsequent Canvas calls draw into pixels. Color Type is set to kN32_SkColorType. Alpha Type is set to kPremul_SkAlphaType. To access pixels after drawing, call flush or peekPixels.

Canvas is returned if all parameters are valid. Valid parameters include: width and height are zero or positive; pixels is not nullptr; rowBytes is zero or large enough to contain width pixels of kN32_SkColorType.

Pass zero for rowBytes to compute rowBytes from width and size of pixel. If rowBytes is greater than zero, it must be equal to or greater than width times bytes required for Color Type.

Pixel buffer size should be height times rowBytes.

Parameters

`width`	pixel column count on Raster Surface created; must be zero or greater
`height`	pixel row count on Raster Surface created; must be zero or greater
`pixels`	pointer to destination pixels buffer; buffer size should be height times rowBytes
`rowBytes`	interval from one Surface row to the next, or zero

Return Value

Canvas if all parameters are valid; otherwise, nullptr

Example

Allocates a three by three bitmap, clears it to white, and draws a black pixel in the center.

Example Output

---
-x-
---

SkCanvas

SkCanvas()

Creates an empty Canvas with no backing device or pixels, with a width and height of zero.

Return Value

empty Canvas

Example

Passes a placeholder to a function that requires one.

Example Output

paint draws text left to right
paint draws text top to bottom
paint draws text top to bottom

SkCanvas

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

Creates Canvas of the specified dimensions without a Surface. Used by Subclasses with custom implementations for draw methods.

If props equals nullptr, Surface Properties are created with Surface Properties Legacy Font Host settings, which choose the pixel striping direction and order. Since a platform may dynamically change its direction when the device is rotated, and since a platform may have multiple monitors with different characteristics, it is best not to rely on this legacy behavior.

Parameters

`width`	zero or greater
`height`	zero or greater
`props`	LCD striping orientation and setting for device independent fonts; may be nullptr

Return Value

Canvas placeholder with dimensions

Example

Example Output

canvas is empty

SkCanvas

explicit SkCanvas(SkBaseDevice* device)

soon

SkCanvas

explicit SkCanvas(const SkBitmap& bitmap)

Construct a canvas that draws into bitmap. Sets SkSurfaceProps::kLegacyFontHost InitType in constructed Surface.

Bitmap is copied so that subsequently editing bitmap will not affect constructed Canvas.

May be deprecated in the future.

Parameters

bitmap width, height, Color Type, Alpha Type, and pixel storage of Raster Surface

Return Value

Canvas that can be used to draw into bitmap

Example

The actual output depends on the installed fonts.

Example Output

-----
---x-
---x-
---x-
---x-
---x-
---x-
-----
---x-
---x-
-----

Enum SkCanvas::ColorBehavior

    enum class ColorBehavior {
        kLegacy,
    };

Constants

SkCanvas

SkCanvas(const SkBitmap& bitmap, ColorBehavior behavior)

Parameters

SkCanvas::ColorBehavior::kLegacy 0 Is a placeholder to allow specialized constructor; has no meaning.

`bitmap`	specifies a bitmap for the canvas to draw into
`behavior`	specializes this constructor; value is unused

Return Value

Canvas that can be used to draw into bitmap

SkCanvas

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

Construct a canvas that draws into bitmap. Use props to match the device characteristics, like LCD striping.

bitmap is copied so that subsequently editing bitmap will not affect constructed Canvas.

Parameters

`bitmap`	width, height, Color Type, Alpha Type, and pixel storage of Raster Surface
`props`	order and orientation of RGB striping; and whether to use device independent fonts

Return Value

Canvas that can be used to draw into bitmap

Example

The actual output depends on the installed fonts.

Example Output

-----
---x-
---x-
---x-
---x-
---x-
---x-
-----
---x-
---x-
-----

~SkCanvas

virtual ~SkCanvas()

Draws saved Layers, if any. Frees up resources used by Canvas.

Example

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.

Property

name	description
getBaseLayerSize	returns size of base Layer in global coordinates
getGrContext	returns GPU Context of the GPU Surface
getMetaData	associates additional data with the canvas
getProps	copies Surface Properties if available
imageInfo	returns Image Info for Canvas
isClipEmpty	returns if Clip is empty
isClipRect	returns if Clip is Rect and not empty

getMetaData

SkMetaData& getMetaData()

Returns storage to associate additional data with the canvas. The storage is freed when Canvas is deleted.

Return Value

storage that can be read from and written to

Example

Example Output

before: (null)
during: Hello!
after: (null)

imageInfo

SkImageInfo imageInfo() const

Returns Image Info for Canvas. If Canvas is not associated with Raster Surface or GPU Surface, returned Color Type is set to kUnknown_SkColorType.

Return Value

dimensions and Color Type of Canvas

Example

Example Output

emptyInfo == canvasInfo

getProps

bool getProps(SkSurfaceProps* props) const

If Canvas is associated with Raster Surface or GPU Surface, copies Surface Properties and returns true. Otherwise, return false and leave props unchanged.

Parameters

props storage for writable SkSurfaceProps

Return Value

true if Surface Properties was copied

Example

Example Output

isRGB:0
isRGB:1

Utility

name	description
accessTopLayerPixels	returns writable pixel access if available
accessTopRasterHandle	returns context that tracks Clip and Matrix
discard	makes Canvas contents undefined
flush	triggers execution of all pending draw operations

flush

void flush()

Triggers the immediate execution of all pending draw operations. If Canvas is associated with GPU Surface, resolves all pending GPU operations. If Canvas is associated with Raster Surface, has no effect; raster draw operations are never deferred.

getBaseLayerSize

virtual SkISize getBaseLayerSize() const

Gets the size of the base or root Layer in global canvas coordinates. The origin of the base Layer is always (0,0). The area available for drawing may be smaller (due to clipping or saveLayer).

Return Value

integral width and height of base Layer

Example

Example Output

clip=10,30
size=20,30

makeSurface

sk_sp<SkSurface> makeSurface(const SkImageInfo& info, const SkSurfaceProps* props = nullptr)

Creates Surface matching info and props, and associates it with Canvas. Returns nullptr if no match found.

If props is nullptr, matches Surface Properties in Canvas. If props is nullptr and Canvas does not have Surface Properties, creates Surface with default Surface Properties.

Parameters

`info`	width, height, Color Type, Alpha Type, and Color Space
`props`	Surface Properties to match; may be nullptr to match Canvas

Return Value

Surface matching info and props, or nullptr if no match is available

Example

Example Output

compatible != nullptr
size = 3, 4

getGrContext

virtual GrContext* getGrContext()

Returns GPU Context of the GPU Surface associated with Canvas.

Return Value

GPU Context, if available; nullptr otherwise

Example

accessTopLayerPixels

void* accessTopLayerPixels(SkImageInfo* info, size_t* rowBytes, SkIPoint* origin = nullptr)

Returns the pixel base address, Image Info, rowBytes, and origin if the pixels can be read directly. The returned address is only valid while Canvas is in scope and unchanged. Any Canvas call or Surface call may invalidate the returned address and other returned values.

If pixels are inaccessible, info, rowBytes, and origin are unchanged.

Parameters

`info`	storage for writable pixels' Image Info; may be nullptr
`rowBytes`	storage for writable pixels' row bytes; may be nullptr
`origin`	storage for Canvas top Layer origin, its top-left corner; may be nullptr

Return Value

address of pixels, or nullptr if inaccessible

Example

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

The Layer and blended result appear on the CPU and GPU but the large dotted "" appear only on the CPU.

accessTopRasterHandle

SkRasterHandleAllocator::Handle accessTopRasterHandle() const

Returns custom context that tracks the Matrix and Clip.

Use Raster Handle Allocator to blend Skia drawing with custom drawing, typically performed by the host platform user interface. The custom context returned is generated by SkRasterHandleAllocator::MakeCanvas, which creates a custom canvas with raster storage for the drawing destination.

Return Value

context of custom allocation

Example

Example Output

context = skia

Pixels

name	description
peekPixels	returns if Canvas has direct access to its pixels
readPixels	copies and converts rectangle of pixels from Canvas
	readPixels(const SkImageInfo& dstInfo, void* dstPixels, size t dstRowBytes, int srcX, int srcY)
	readPixels(const SkPixmap& pixmap, int srcX, int srcY)
	readPixels(const SkBitmap& bitmap, int srcX, int srcY)
writePixels	copies and converts rectangle of pixels to Canvas
	writePixels(const SkImageInfo& info, const void* pixels, size t rowBytes, int x, int y)
	writePixels(const SkBitmap& bitmap, int x, int y)

peekPixels

bool peekPixels(SkPixmap* pixmap)

Returns true if Canvas has direct access to its pixels.

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

pixmap is valid only while Canvas is in scope and unchanged. Any Canvas or Surface call may invalidate the pixmap values.

Parameters

pixmap storage for pixel state if pixels are readable; otherwise, ignored

Return Value

true if Canvas has direct access to pixels

Example

Example Output

width=256 height=256

readPixels

bool readPixels(const SkImageInfo& dstInfo, void* dstPixels, size_t dstRowBytes, int srcX, int srcY)

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:

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.

Parameters

`dstInfo`	width, height, Color Type, and Alpha Type of dstPixels
`dstPixels`	storage for pixels; dstInfo.height() times dstRowBytes, or larger
`dstRowBytes`	size of one destination row; dstInfo.width() times pixel size, or larger
`srcX`	offset into readable pixels in x; may be negative
`srcY`	offset into readable pixels in y; may be negative

Return Value

true if pixels were copied

Example

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.

Example

Canvas returned by Raster Surface has Premultiplied pixel values. clear takes Unpremultiplied input with Color Alpha equal 0x80 and Color RGB equal 0x55, 0xAA, 0xFF. Color RGB is multiplied by Color Alpha to generate Premultiplied value 0x802B5580. readPixels converts pixel back to Unpremultiplied value 0x8056A9FF, introducing error.

Example Output

pixel = 802b5580
pixel = 8056a9ff

Parameters

`pixmap`	storage for pixels copied from Canvas
`srcX`	offset into readable pixels in x; may be negative
`srcY`	offset into readable pixels in y; may be negative

Return Value

true if pixels were copied

Example

clear takes Unpremultiplied input with Color Alpha equal 0x80 and Color RGB equal 0x55, 0xAA, 0xFF. Color RGB is multiplied by Color Alpha to generate Premultiplied value 0x802B5580.

Example Output

pixel = 802b5580

Parameters

`bitmap`	storage for pixels copied from Canvas
`srcX`	offset into readable pixels in x; may be negative
`srcY`	offset into readable pixels in y; may be negative

Return Value

true if pixels were copied

Example

clear takes Unpremultiplied input with Color Alpha equal 0x80 and Color RGB equal 0x55, 0xAA, 0xFF. Color RGB is multiplied by Color Alpha to generate Premultiplied value 0x802B5580.

Example Output

pixel = 802b5580

writePixels

bool writePixels(const SkImageInfo& info, const void* pixels, size_t rowBytes, int x, int y)

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:

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.

Parameters

`info`	width, height, Color Type, and Alpha Type of pixels
`pixels`	pixels to copy, of size info.height() times rowBytes, or larger
`rowBytes`	size of one row of pixels; info.width() times pixel size, or larger
`x`	offset into Canvas writable pixels in x; may be negative
`y`	offset into Canvas writable pixels in y; may be negative

Return Value

true if pixels were written to Canvas

Example

Parameters

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

Return Value

true if pixels were written to Canvas

Example

State Stack

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, Matrix, and Draw Filter. Clip describes the area that may be drawn to. Matrix transforms the geometry. Draw Filter (deprecated on most platforms) modifies the paint before drawing.

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

restore, restoreToCount, and

Example

Draw to ever smaller clips; then restore drawing to full canvas. Note that the second clipRect is not permitted to enlarge Clip.

Each Clip uses the current Matrix for its coordinates.

Example

While clipRect is given the same rectangle twice, Matrix makes the second clipRect draw at half the size of the first.

save

int save()

Saves Matrix, Clip, and Draw Filter (Draw Filter deprecated on most platforms). Calling restore discards changes to Matrix, Clip, and Draw Filter, restoring the Matrix, Clip, and Draw Filter to their state when save was called.

Matrix may be changed by translate, scale, rotate, skew, concat, setMatrix, and resetMatrix. Clip may be changed by clipRect, clipRRect, clipPath, clipRegion.

Saved Canvas state is put on a stack; multiple calls to save should be balance by an equal number of calls to restore.

Call restoreToCount with result to restore this and subsequent saves.

Return Value

depth of saved stack

Example

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.

restore

void restore()

Removes changes to Matrix, Clip, and Draw Filter since Canvas state was last saved. The state is removed from the stack.

Does nothing if the stack is empty.

Example

getSaveCount

int getSaveCount() const

Returns the number of saved states, each containing: Matrix, Clip, and Draw Filter. Equals the number of save calls less the number of restore calls plus one. The save count of a new canvas is one.

Return Value

depth of save state stack

Example

Example Output

depth = 1
depth = 2
depth = 1

restoreToCount

void restoreToCount(int saveCount)

Restores state to Matrix, Clip, and Draw Filter values when save, saveLayer, saveLayerPreserveLCDTextRequests, or saveLayerAlpha returned saveCount.

Does nothing if saveCount is greater than state stack count. Restores state to initial values if saveCount is less than or equal to one.

Parameters

saveCount depth of state stack to restore

Example

Example Output

depth = 1
depth = 3
depth = 1

Layer

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.

saveLayer

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

Saves Matrix, Clip, and Draw Filter (Draw Filter deprecated on most platforms), and allocates a Bitmap for subsequent drawing. Calling restore discards changes to Matrix, Clip, and Draw Filter, and draws the Bitmap.

Matrix may be changed by translate, scale, rotate, skew, concat, setMatrix, and resetMatrix. Clip may be changed by clipRect, clipRRect, clipPath, clipRegion.

Rect bounds suggests but does not define the Bitmap size. To clip drawing to a specific rectangle, use clipRect.

Optional Paint paint applies Color Alpha, Color Filter, Image Filter, and Blend Mode when restore is called.

Call restoreToCount with returned value to restore this and subsequent saves.

Parameters

`bounds`	hint to limit the size of the Layer; may be nullptr
`paint`	graphics state for Layer; may be nullptr

Return Value

depth of saved stack

Example

Rectangles are blurred by Image Filter when restore draws Layer to main Canvas.

Parameters

`bounds`	hint to limit the size of Layer; may be nullptr
`paint`	graphics state for Layer; may be nullptr

Return Value

depth of saved stack

Example

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.

saveLayerPreserveLCDTextRequests

int saveLayerPreserveLCDTextRequests(const SkRect* bounds, const SkPaint* paint)

Saves Matrix, Clip, and Draw Filter (Draw Filter deprecated on most platforms), and allocates a Bitmap for subsequent drawing. LCD Text is preserved when the Layer is drawn to the prior Layer.

Calling restore discards changes to Matrix, Clip, and Draw Filter, and draws Layer.

Matrix may be changed by translate, scale, rotate, skew, concat, setMatrix, and resetMatrix. Clip may be changed by clipRect, clipRRect, clipPath, clipRegion. Rect bounds suggests but does not define the Layer size. To clip drawing to a specific rectangle, use clipRect.

Optional Paint paint applies Color Alpha, Color Filter, Image Filter, and Blend Mode when restore is called.

Call restoreToCount with returned value to restore this and subsequent saves.

Draw text on an opaque background so that LCD Text blends correctly with the prior Layer. LCD Text drawn on a background with transparency may result in incorrect blending.

Parameters

`bounds`	hint to limit the size of Layer; may be nullptr
`paint`	graphics state for Layer; may be nullptr

Return Value

depth of saved stack

Example

saveLayerAlpha

int saveLayerAlpha(const SkRect* bounds, U8CPU alpha)

Saves Matrix, Clip, and Draw Filter (Draw Filter deprecated on most platforms), and allocates Bitmap for subsequent drawing.

Calling restore discards changes to Matrix, Clip, and Draw Filter, and blends Layer with alpha opacity onto prior Layer.

Matrix may be changed by translate, scale, rotate, skew, concat, setMatrix, and resetMatrix. Clip may be changed by clipRect, clipRRect, clipPath, clipRegion.

Rect bounds suggests but does not define Layer size. To clip drawing to a specific rectangle, use clipRect.

alpha of zero is fully transparent, 255 is fully opaque.

Call restoreToCount with returned value to restore this and subsequent saves.

Parameters

`bounds`	hint to limit the size of Layer; may be nullptr
`alpha`	opacity of Layer

Return Value

depth of saved stack

Example

Enum SkCanvas::_anonymous

    enum {
        kPreserveLCDText SaveLayerFlag = 1 << 1,
        kInitWithPrevious SaveLayerFlag = 1 << 2,
        kDontClipToLayer Legacy SaveLayerFlag = kDontClipToLayer_PrivateSaveLayerFlag,
    };

SaveLayerFlags provides options that may be used in any combination in SaveLayerRec, defining how Layer allocated by saveLayer operates.

Constants

`SkCanvas::kPreserveLCDText_SaveLayerFlag`	2	Creates Layer for LCD text. Flag is ignored if Layer Paint contains Image Filter or Color Filter.
`SkCanvas::kInitWithPrevious_SaveLayerFlag`	4	Initializes Layer with the contents of the previous Layer.
`SkCanvas::kDontClipToLayer_Legacy_SaveLayerFlag`	0x80000000	soon

Example

Canvas Layer captures red and blue circles scaled up by four. scalePaint blends Layer back with transparency.

Struct SkCanvas::SaveLayerRec

    struct SaveLayerRec {
        SaveLayerRec*(...

        const SkRect*           fBounds;
        const SkPaint*          fPaint;
        const SkImageFilter*    fBackdrop;
        SaveLayerFlags          fSaveLayerFlags;
    };

SaveLayerRec contains the state used to create the Layer.

const SkRect* fBounds

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.

const SkPaint* fPaint

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.

const SkImageFilter* fBackdrop

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.

const SkImage* fClipMask

restore clips Layer by the Color Alpha channel of fClipMask when Layer is copied to Device. fClipMask may be nullptr. .

const SkMatrix* fClipMatrix

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.

SaveLayerFlags fSaveLayerFlags

fSaveLayerFlags are used to create Layer without transparency, create Layer for LCD text, and to create Layer with the contents of the previous Layer.

Example

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.

SaveLayerRec

SaveLayerRec()

Sets fBounds, fPaint, and fBackdrop to nullptr. Clears fSaveLayerFlags.

Return Value

empty SaveLayerRec

Example

Example Output

rec1 == rec2

Parameters

`bounds`	Layer dimensions; may be nullptr
`paint`	applied to Layer when overlaying prior Layer; may be nullptr
`saveLayerFlags`	SaveLayerRec options to modify Layer

Return Value

SaveLayerRec with empty backdrop

Example

Example Output

rec1 == rec2

Parameters

`bounds`	Layer dimensions; may be nullptr
`paint`	applied to Layer when overlaying prior Layer; may be nullptr
`backdrop`	prior Layer copied with Image Filter; may be nullptr
`saveLayerFlags`	SaveLayerRec options to modify Layer

Return Value

SaveLayerRec fully specified

Example

Example Output

rec1 == rec2

Parameters

`bounds`	Layer dimensions; may be nullptr
`paint`	graphics state applied to Layer when overlaying prior Layer; may be nullptr
`backdrop`	prior Layer copied with Image Filter; may be nullptr
`clipMask`	clip applied to Layer; may be nullptr
`clipMatrix`	matrix applied to clipMask; may be nullptr to use identity matrix
`saveLayerFlags`	SaveLayerRec options to modify Layer

Return Value

SaveLayerRec fully specified

Parameters

layerRec Layer state

Return Value

depth of save state stack

Example

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.

Matrix

translate

void translate(SkScalar dx, SkScalar dy)

Translate Matrix by dx along the x-axis and dy along the y-axis.

Mathematically, replace Matrix with a translation matrix Premultiplied with Matrix.

This has the effect of moving the drawing by (dx, dy) before transforming the result with Matrix.

Parameters

`dx`	distance to translate in x
`dy`	distance to translate in y

Example

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).

scale

void scale(SkScalar sx, SkScalar sy)

Scale Matrix by sx on the x-axis and sy on the y-axis.

Mathematically, replace Matrix with a scale matrix Premultiplied with Matrix.

This has the effect of scaling the drawing by (sx, sy) before transforming the result with Matrix.

Parameters

`sx`	amount to scale in x
`sy`	amount to scale in y

Example

rotate

void rotate(SkScalar degrees)

Rotate Matrix by degrees. Positive degrees rotates clockwise.

Mathematically, replace Matrix with a rotation matrix Premultiplied with Matrix.

This has the effect of rotating the drawing by degrees before transforming the result with Matrix.

Parameters

degrees amount to rotate, in degrees

Example

Draw clock hands at time 5:10. The hour hand and minute hand point up and are rotated clockwise.

Parameters

`degrees`	amount to rotate, in degrees
`px`	x-coordinate of the point to rotate about
`py`	y-coordinate of the point to rotate about

Example

skew

void skew(SkScalar sx, SkScalar sy)

Skew Matrix by sx on the x-axis and sy on the y-axis. A positive value of sx skews the drawing right as y increases; a positive value of sy skews the drawing down as x increases.

Mathematically, replace Matrix with a skew matrix Premultiplied with Matrix.

This has the effect of skewing the drawing by (sx, sy) before transforming the result with Matrix.

Parameters

`sx`	amount to skew in x
`sy`	amount to skew in y

Example

Black text mimics an oblique text style by using a negative skew in x that shifts the geometry to the right as the y values decrease. Red text uses a positive skew in y to shift the geometry down as the x values increase. Blue text combines x and y skew to rotate and scale.

concat

void concat(const SkMatrix& matrix)

Replace Matrix with matrix Premultiplied with existing Matrix.

This has the effect of transforming the drawn geometry by matrix, before transforming the result with existing Matrix.

Parameters

matrix matrix to Premultiply with existing Matrix

Example

setMatrix

void setMatrix(const SkMatrix& matrix)

Replace Matrix with matrix. Unlike concat, any prior matrix state is overwritten.

Parameters

matrix matrix to copy, replacing existing Matrix

Example

resetMatrix

void resetMatrix()

Sets Matrix to the identity matrix. Any prior matrix state is overwritten.

Example

getTotalMatrix

const SkMatrix& getTotalMatrix() const

Returns Matrix. This does not account for translation by Device or Surface.

Return Value

Matrix in Canvas

Example

Example Output

isIdentity true

Clip

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

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.

clipRect

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

Replace Clip with the intersection or difference of Clip and rect, with an Aliased or Anti-aliased clip edge. rect is transformed by Matrix before it is combined with Clip.

Parameters

`rect`	Rect to combine with Clip
`op`	Clip Op to apply to Clip
`doAntiAlias`	true if Clip is to be Anti-aliased

Example

Parameters

`rect`	Rect to combine with Clip
`op`	Clip Op to apply to Clip

Example

Parameters

`rect`	Rect to combine with Clip
`doAntiAlias`	true if Clip is to be Anti-aliased

Example

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.

androidFramework_setDeviceClipRestriction

void androidFramework_setDeviceClipRestriction(const SkIRect& rect)

Sets the maximum clip rectangle, which can be set by clipRect, clipRRect and clipPath and intersect the current clip with the specified rect. The maximum clip affects only future clipping operations; it is not retroactive. The clip restriction is not recorded in pictures.

Pass an empty rect to disable maximum clip.

Parameters

clipRRect

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

Replace Clip with the intersection or difference of Clip and rrect, with an Aliased or Anti-aliased clip edge. rrect is transformed by Matrix before it is combined with Clip.

Parameters

rect maximum allowed clip in device coordinates

`rrect`	Round Rect to combine with Clip
`op`	Clip Op to apply to Clip
`doAntiAlias`	true if Clip is to be Anti-aliased

Example

Parameters

`rrect`	Round Rect to combine with Clip
`op`	Clip Op to apply to Clip

Example

Parameters

`rrect`	Round Rect to combine with Clip
`doAntiAlias`	true if Clip is to be Anti-aliased

Example

clipPath

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

Replace Clip with the intersection or difference of Clip and path, with an Aliased or Anti-aliased clip edge. Path Fill Type determines if path describes the area inside or outside its contours; and if Path Contour overlaps itself or another Path Contour, whether the overlaps form part of the area. path is transformed by Matrix before it is combined with Clip.

Parameters

`path`	Path to combine with Clip
`op`	Clip Op to apply to Clip
`doAntiAlias`	true if Clip is to be Anti-aliased

Example

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.

Parameters

`path`	Path to combine with Clip
`op`	Clip Op to apply to Clip

Example

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.

Parameters

`path`	Path to combine with Clip
`doAntiAlias`	true if Clip is to be Anti-aliased

Example

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.

setAllowSimplifyClip

void setAllowSimplifyClip(bool allow)

Only used for testing. Set to simplify clip stack using PathOps.

clipRegion

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

Replace Clip with the intersection or difference of Clip and Region deviceRgn. Resulting Clip is Aliased; pixels are fully contained by the clip. deviceRgn is unaffected by Matrix.

Parameters

`deviceRgn`	Region to combine with Clip
`op`	Clip Op to apply to Clip

Example

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.

quickReject

bool quickReject(const SkRect& rect) const

Return true if Rect rect, transformed by Matrix, can be quickly determined to be outside of Clip. May return false even though rect is outside of Clip.

Use to check if an area to be drawn is clipped out, to skip subsequent draw calls.

Parameters

rect Rect to compare with Clip

Return Value

true if rect, transformed by Matrix, does not intersect Clip

Example

Example Output

quickReject true
quickReject false

Parameters

path Path to compare with Clip

Return Value

true if path, transformed by Matrix, does not intersect Clip

Example

Example Output

quickReject true
quickReject false

getLocalClipBounds

SkRect getLocalClipBounds() const

Return bounds of Clip, transformed by inverse of Matrix. If Clip is empty, return SkRect::MakeEmpty, where all Rect sides equal zero.

Rect returned is outset by one to account for partial pixel coverage if Clip is Anti-aliased.

Return Value

bounds of Clip in local coordinates

Example

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 in x and y scales the local bounds by 1/2 in x and y.

Example Output

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

Parameters

bounds Rect of Clip in local coordinates

Return Value

true if Clip bounds is not empty

Example

Example Output

local bounds empty = false
local bounds empty = true

getDeviceClipBounds

SkIRect getDeviceClipBounds() const

Return IRect bounds of Clip, unaffected by Matrix. If Clip is empty, return SkRect::MakeEmpty, where all Rect sides equal zero.

Unlike getLocalClipBounds, returned IRect is not outset.

Return Value

bounds of Clip in Device coordinates

Example

Initial bounds is device bounds, not outset. Clipped bounds is clipPath bounds, not outset. Scaling the canvas by 1/2 in x and y scales the device bounds by 1/2 in x and y.

Example Output

left:0  top:0  right:256  bottom:256
left:30  top:130  right:120  bottom:230
left:15  top:65  right:60  bottom:115

Parameters

bounds Rect of Clip in device coordinates

Return Value

true if Clip bounds is not empty

Example

Example Output

device bounds empty = false
device bounds empty = true

Draw

name	description
clear	fills Clip with Color
drawAnnotation	associates a Rect with a key-value pair
	drawAnnotation(const SkRect& rect, const char key[], SkData* value)
	drawAnnotation(const SkRect& rect, const char key[], const sk sp<SkData>& value)
drawArc	draws Arc using Clip, Matrix, and Paint
drawAtlas	draws sprites using Clip, Matrix, and Paint
	drawAtlas(const SkImage* atlas, const SkRSXform xform[], const SkRect tex[], const SkColor colors[], int count, SkBlendMode mode, const SkRect* cullRect, const SkPaint* paint)
	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)
	drawAtlas(const SkImage* atlas, const SkRSXform xform[], const SkRect tex[], int count, const SkRect* cullRect, const SkPaint* paint)
	drawAtlas(const sk sp<SkImage>& atlas, const SkRSXform xform[], const SkRect tex[], int count, const SkRect* cullRect, const SkPaint* paint)
drawCircle	draws Circle using Clip, Matrix, and Paint
	drawCircle(SkScalar cx, SkScalar cy, SkScalar radius, const SkPaint& paint)
	drawCircle(SkPoint center, SkScalar radius, const SkPaint& paint)
drawColor	fills Clip with Color and Blend Mode
drawDRRect	draws double Round Rect stroked or filled
drawDrawable	draws Drawable, encapsulated drawing commands
	drawDrawable(SkDrawable* drawable, const SkMatrix* matrix = nullptr)
	drawDrawable(SkDrawable* drawable, SkScalar x, SkScalar y)
drawIRect	draws IRect using Clip, Matrix, and Paint
drawLine	draws line segment between two points
	drawLine(SkScalar x0, SkScalar y0, SkScalar x1, SkScalar y1, const SkPaint& paint)
	drawLine(SkPoint p0, SkPoint p1, const SkPaint& paint)
drawOval	draws Oval using Clip, Matrix, and Paint
drawPaint	fills Clip with Paint
drawPatch	draws Coons_Patch
	drawPatch(const SkPoint cubics[12], const SkColor colors[4], const SkPoint texCoords[4], SkBlendMode mode, const SkPaint& paint)
	drawPatch(const SkPoint cubics[12], const SkColor colors[4], const SkPoint texCoords[4], const SkPaint& paint)
drawPath	draws Path using Clip, Matrix, and Paint
drawPicture	draws Picture using Clip and Matrix
	drawPicture(const SkPicture* picture)
	drawPicture(const sk sp<SkPicture>& picture)
	drawPicture(const SkPicture* picture, const SkMatrix* matrix, const SkPaint* paint)
	drawPicture(const sk sp<SkPicture>& picture, const SkMatrix* matrix, const SkPaint* paint)
drawPoint	draws point at (x, y) position
	drawPoint(SkScalar x, SkScalar y, const SkPaint& paint)
	drawPoint(SkPoint p, const SkPaint& paint)
drawPoints	draws array as points, lines, polygon
drawRRect	draws Round Rect using Clip, Matrix, and Paint
drawRect	draws Rect using Clip, Matrix, and Paint
drawRegion	draws Region using Clip, Matrix, and Paint
drawRoundRect	draws Round Rect using Clip, Matrix, and Paint
drawVertices	draws Vertices, a triangle mesh
	drawVertices(const SkVertices* vertices, SkBlendMode mode, const SkPaint& paint)
	drawVertices(const sk sp<SkVertices>& vertices, SkBlendMode mode, const SkPaint& paint)

drawColor

void drawColor(SkColor color, SkBlendMode mode = SkBlendMode::kSrcOver)

Fill Clip with Color color. mode determines how Color ARGB is combined with destination.

Parameters

`color`	Unpremultiplied Color ARGB
`mode`	SkBlendMode used to combine source color and destination

Example

clear

void clear(SkColor color)

Fill Clip with Color color using SkBlendMode::kSrc. This has the effect of replacing all pixels contained by Clip with color.

Parameters

color

Unpremultiplied Color ARGB

Example

discard

void discard()

Make Canvas contents undefined. Subsequent calls that read Canvas pixels, such as drawing with SkBlendMode, return undefined results. discard does not change Clip or Matrix.

discard may do nothing, depending on the implementation of Surface or Device that created Canvas.

discard allows optimized performance on subsequent draws by removing cached data associated with Surface or Device. It is not necessary to call discard once done with Canvas; any cached data is deleted when owning Surface or Device is deleted.

drawPaint

void drawPaint(const SkPaint& paint)

Fill Clip with Paint paint. Paint components Mask Filter, Shader, Color Filter, Image Filter, and Blend Mode affect drawing; Path Effect in paint is ignored.

Parameters

paint graphics state used to fill Canvas

Example

Enum SkCanvas::PointMode

    enum PointMode {
        kPoints PointMode,
        kLines PointMode,
        kPolygon PointMode,
    };

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

Constants

`SkCanvas::kPoints_PointMode`	0	Draw each point separately.
`SkCanvas::kLines_PointMode`	1	Draw each pair of points as a line segment.
`SkCanvas::kPolygon_PointMode`	2	Draw the array of points as a open polygon.

Example

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.

drawPoints

void drawPoints(PointMode mode, size_t count, const SkPoint pts[], const SkPaint& paint)

Draw pts using Clip, Matrix and Paint paint. count is the number of points; if count is less than one, has no effect. mode may be one of: kPoints PointMode, kLines PointMode, or kPolygon PointMode.

If mode is kPoints PointMode, the shape of point drawn depends on paint Paint Stroke Cap. If paint is set to SkPaint::kRound Cap, each point draws a circle of diameter Paint Stroke Width. If paint is set to SkPaint::kSquare Cap or SkPaint::kButt Cap, each point draws a square of width and height Paint Stroke Width.

If mode is kLines PointMode, each pair of points draws a line segment. One line is drawn for every two points; each point is used once. If count is odd, the final point is ignored.

If mode is kPolygon PointMode, each adjacent pair of points draws a line segment. count minus one lines are drawn; the first and last point are used once.

Each line segment respects paint Paint Stroke Cap and Paint Stroke Width. Paint Style is ignored, as if were set to SkPaint::kStroke Style.

Always draws each element one at a time; is not affected by Paint Stroke Join, and unlike drawPath, does not create a mask from all points and lines before drawing.

Parameters

`mode`	whether pts draws points or lines
`count`	number of points in the array
`pts`	array of points to draw
`paint`	stroke, blend, color, and so on, used to draw

Example

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.

drawPoint

void drawPoint(SkScalar x, SkScalar y, const SkPaint& paint)

Draw point at (x, y) using Clip, Matrix and Paint paint.

The shape of point drawn depends on paint Paint Stroke Cap. If paint is set to SkPaint::kRound Cap, draw a circle of diameter Paint Stroke Width. If paint is set to SkPaint::kSquare Cap or SkPaint::kButt Cap, draw a square of width and height Paint Stroke Width. Paint Style is ignored, as if were set to SkPaint::kStroke Style.

Parameters

`x`	left edge of circle or square
`y`	top edge of circle or square
`paint`	stroke, blend, color, and so on, used to draw

Example

Parameters

`p`	top-left edge of circle or square
`paint`	stroke, blend, color, and so on, used to draw

Example

drawLine

void drawLine(SkScalar x0, SkScalar y0, SkScalar x1, SkScalar y1, const SkPaint& paint)

Draws line segment from (x0, y0) to (x1, y1) using Clip, Matrix, and Paint paint. In paint: Paint Stroke Width describes the line thickness; Paint Stroke Cap draws the end rounded or square; Paint Style is ignored, as if were set to SkPaint::kStroke Style.

Parameters

`x0`	start of line segment on x-axis
`y0`	start of line segment on y-axis
`x1`	end of line segment on x-axis
`y1`	end of line segment on y-axis
`paint`	stroke, blend, color, and so on, used to draw

Example

Parameters

`p0`	start of line segment
`p1`	end of line segment
`paint`	stroke, blend, color, and so on, used to draw

Example

drawRect

void drawRect(const SkRect& rect, const SkPaint& paint)

Draw Rect rect using Clip, Matrix, and Paint paint. In paint: Paint Style determines if rectangle is stroked or filled; if stroked, Paint Stroke Width describes the line thickness, and Paint Stroke Join draws the corners rounded or square.

Parameters

`rect`	rectangle to draw
`paint`	stroke or fill, blend, color, and so on, used to draw

Example

drawIRect

void drawIRect(const SkIRect& rect, const SkPaint& paint)

Draw IRect rect using Clip, Matrix, and Paint paint. In paint: Paint Style determines if rectangle is stroked or filled; if stroked, Paint Stroke Width describes the line thickness, and Paint Stroke Join draws the corners rounded or square.

Parameters

`rect`	rectangle to draw
`paint`	stroke or fill, blend, color, and so on, used to draw

Example

drawRegion

void drawRegion(const SkRegion& region, const SkPaint& paint)

Draw Region region using Clip, Matrix, and Paint paint. In paint: Paint Style determines if rectangle is stroked or filled; if stroked, Paint Stroke Width describes the line thickness, and Paint Stroke Join draws the corners rounded or square.

Parameters

`region`	region to draw
`paint`	Paint stroke or fill, blend, color, and so on, used to draw

Example

drawOval

void drawOval(const SkRect& oval, const SkPaint& paint)

Draw Oval oval using Clip, Matrix, and Paint. In paint: Paint Style determines if Oval is stroked or filled; if stroked, Paint Stroke Width describes the line thickness.

Parameters

`oval`	Rect bounds of Oval
`paint`	Paint stroke or fill, blend, color, and so on, used to draw

Example

drawRRect

void drawRRect(const SkRRect& rrect, const SkPaint& paint)

Draw Round Rect rrect using Clip, Matrix, and Paint paint. In paint: Paint Style determines if rrect is stroked or filled; if stroked, Paint Stroke Width describes the line thickness.

rrect may represent a rectangle, circle, oval, uniformly rounded rectangle, or may have any combination of positive non-square radii for the four corners.

Parameters

`rrect`	Round Rect with up to eight corner radii to draw
`paint`	Paint stroke or fill, blend, color, and so on, used to draw

Example

drawDRRect

void drawDRRect(const SkRRect& outer, const SkRRect& inner, const SkPaint& paint)

Draw Round Rect outer and inner using Clip, Matrix, and Paint paint. outer must contain inner or the drawing is undefined. In paint: Paint Style determines if Round Rect is stroked or filled; if stroked, Paint Stroke Width describes the line thickness. If stroked and Round Rect corner has zero length radii, Paint Stroke Join can draw corners rounded or square.

GPU-backed platforms optimize drawing when both outer and inner are concave and outer contains inner. These platforms may not be able to draw Path built with identical data as fast.

Parameters

`outer`	Round Rect outer bounds to draw
`inner`	Round Rect inner bounds to draw
`paint`	Paint stroke or fill, blend, color, and so on, used to draw

Example

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.

drawCircle

void drawCircle(SkScalar cx, SkScalar cy, SkScalar radius, const SkPaint& paint)

Draw Circle at (cx, cy) with radius using Clip, Matrix, and Paint paint. If radius is zero or less, nothing is drawn. In paint: Paint Style determines if Circle is stroked or filled; if stroked, Paint Stroke Width describes the line thickness.

Parameters

`cx`	Circle center on the x-axis
`cy`	Circle center on the y-axis
`radius`	half the diameter of Circle
`paint`	Paint stroke or fill, blend, color, and so on, used to draw

Example

Parameters

`center`	Circle center
`radius`	half the diameter of Circle
`paint`	Paint stroke or fill, blend, color, and so on, used to draw

Example

drawArc

void drawArc(const SkRect& oval, SkScalar startAngle, SkScalar sweepAngle, bool useCenter,
             const SkPaint& paint)

Draw Arc using Clip, Matrix, and Paint paint.

Arc is part of Oval bounded by oval, sweeping from startAngle to startAngle plus sweepAngle. startAngle and sweepAngle are in degrees.

startAngle of zero places start point at the right middle edge of oval. A positive sweepAngle places Arc end point clockwise from start point; a negative sweepAngle places Arc end point counterclockwise from start point. sweepAngle may exceed 360 degrees, a full circle. If useCenter is true, draw a wedge that includes lines from oval center to Arc end points. If useCenter is false, draw Arc between end points.

If Rect oval is empty or sweepAngle is zero, nothing is drawn.

Parameters

`oval`	Rect bounds of Oval containing Arc to draw
`startAngle`	angle in degrees where Arc begins
`sweepAngle`	sweep angle in degrees; positive is clockwise
`useCenter`	if true, include the center of the oval
`paint`	Paint stroke or fill, blend, color, and so on, used to draw

Example

drawRoundRect

void drawRoundRect(const SkRect& rect, SkScalar rx, SkScalar ry, const SkPaint& paint)

Draw Round Rect bounded by Rect rect, with corner radii (rx, ry) using Clip, Matrix, and Paint paint.

In paint: Paint Style determines if Round Rect is stroked or filled; if stroked, Paint Stroke Width describes the line thickness. If rx or ry are less than zero, they are treated as if they are zero. If rx plus ry exceeds rect width or rect height, radii are scaled down to fit. If rx and ry are zero, Round Rect is drawn as Rect and if stroked is affected by Paint Stroke Join.

Parameters

`rect`	Rect bounds of Round Rect to draw
`rx`	axis length in x of oval describing rounded corners
`ry`	axis length in y of oval describing rounded corners
`paint`	stroke, blend, color, and so on, used to draw

Example

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.

drawPath

void drawPath(const SkPath& path, const SkPaint& paint)

Draw Path path using Clip, Matrix, and Paint paint. Path contains an array of Path Contour, each of which may be open or closed.

In paint: Paint Style determines if Round Rect is stroked or filled: if filled, Path Fill Type determines whether Path Contour describes inside or outside of fill; if stroked, Paint Stroke Width describes the line thickness, Paint Stroke Cap describes line ends, and Paint Stroke Join describes how corners are drawn.

Parameters

`path`	Path to draw
`paint`	stroke, blend, color, and so on, used to draw

Example

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.

Draw Image

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.

drawImage

void drawImage(const SkImage* image, SkScalar left, SkScalar top, const SkPaint* paint = nullptr)

Draw Image image, with its top-left corner at (left, top), using Clip, Matrix, and optional Paint paint.

If paint is supplied, apply Color Filter, Color Alpha, Image Filter, Blend Mode, and Draw Looper. If image is kAlpha_8_SkColorType, apply Shader. If paint contains Mask Filter, generate mask from image bounds. 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.

Parameters

`image`	uncompressed rectangular map of pixels
`left`	left side of image
`top`	top side of image
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr

Example

Parameters

`image`	uncompressed rectangular map of pixels
`left`	left side of image
`top`	pop side of image
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr

Example

Enum SkCanvas::SrcRectConstraint

    enum SrcRectConstraint {
        kStrict SrcRectConstraint,
        kFast SrcRectConstraint,
    };

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.

Constants

`SkCanvas::kStrict_SrcRectConstraint`	Requires Image_Filter to respect source Rect,	sampling only inside of its bounds, possibly with a performance penalty.
`SkCanvas::kFast_SrcRectConstraint`	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

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.

drawImageRect

void drawImageRect(const SkImage* image, const SkRect& src, const SkRect& dst, const SkPaint* paint,
                   SrcRectConstraint constraint = kStrict_SrcRectConstraint)

Draw Rect src of Image image, scaled and translated to fill Rect dst. Additionally transform draw using Clip, Matrix, and optional Paint paint.

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.

constraint set to kStrict SrcRectConstraint limits Paint Filter Quality to sample within src; set to kFast SrcRectConstraint allows sampling outside to improve performance.

Parameters

`image`	Image containing pixels, dimensions, and format
`src`	source Rect of image to draw from
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr
`constraint`	filter strictly within src or draw faster

Example

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.

Parameters

`image`	Image containing pixels, dimensions, and format
`isrc`	source IRect of image to draw from
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr
`constraint`	filter strictly within isrc or draw faster

Example

Parameters

`image`	Image containing pixels, dimensions, and format
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr
`constraint`	filter strictly within image or draw faster

Example

Parameters

`image`	Image containing pixels, dimensions, and format
`src`	source Rect of image to draw from
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr
`constraint`	filter strictly within src or draw faster

Example

Canvas scales and translates; transformation from src to dst also scales. The two matrices are concatenated to create the final transformation.

Parameters

`image`	Image containing pixels, dimensions, and format
`isrc`	source IRect of image to draw from
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr
`constraint`	filter strictly within image or draw faster

Example

Parameters

`image`	Image containing pixels, dimensions, and format
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr
`constraint`	filter strictly within image or draw faster

Example

drawImageNine

void drawImageNine(const SkImage* image, const SkIRect& center, const SkRect& dst,
                   const SkPaint* paint = nullptr)

Draw 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.

Parameters

`image`	Image containing pixels, dimensions, and format
`center`	IRect edge of image corners and sides
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr

Example

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.

Parameters

`image`	Image containing pixels, dimensions, and format
`center`	IRect edge of image corners and sides
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr

Example

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.

drawBitmap

void drawBitmap(const SkBitmap& bitmap, SkScalar left, SkScalar top, const SkPaint* paint = nullptr)

Draw Bitmap bitmap, with its top-left corner at (left, top), using Clip, Matrix, and optional Paint paint.

If Paint paint is not nullptr, apply Color Filter, Color Alpha, Image Filter, Blend Mode, and Draw Looper. If bitmap is kAlpha_8_SkColorType, apply Shader. If paint contains Mask Filter, generate mask from bitmap bounds.

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.

Parameters

`bitmap`	Bitmap containing pixels, dimensions, and format
`left`	left side of bitmap
`top`	top side of bitmap
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr

Example

drawBitmapRect

void drawBitmapRect(const SkBitmap& bitmap, const SkRect& src, const SkRect& dst,
                    const SkPaint* paint, SrcRectConstraint constraint = kStrict_SrcRectConstraint)

Draw Rect src of Bitmap bitmap, scaled and translated to fill Rect dst. Additionally transform draw using Clip, Matrix, and optional Paint paint.

If Paint paint is supplied, apply Color Filter, Color Alpha, Image Filter, Blend Mode, and Draw Looper. If bitmap is kAlpha_8_SkColorType, apply Shader. If paint contains Mask Filter, generate mask from bitmap bounds.

constraint set to kStrict SrcRectConstraint limits Paint Filter Quality to sample within src; set to kFast SrcRectConstraint allows sampling outside to improve performance.

Parameters

`bitmap`	Bitmap containing pixels, dimensions, and format
`src`	source Rect of image to draw from
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr
`constraint`	filter strictly within src or draw faster

Example

Parameters

`bitmap`	Bitmap containing pixels, dimensions, and format
`isrc`	source IRect of image to draw from
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr
`constraint`	sample strictly within isrc, or draw faster

Example

Parameters

`bitmap`	Bitmap containing pixels, dimensions, and format
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr
`constraint`	filter strictly within bitmap or draw faster

Example

drawBitmapNine

void drawBitmapNine(const SkBitmap& bitmap, const SkIRect& center, const SkRect& dst,
                    const SkPaint* paint = nullptr)

Draw 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.

Parameters

`bitmap`	Bitmap containing pixels, dimensions, and format
`center`	IRect edge of image corners and sides
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr

Example

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.

Struct SkCanvas::Lattice

    struct Lattice {
        enum RectType ...

        const int*      fXDivs;
        const int*      fYDivs;
        const RectType* fRectTypes;
        int             fXCount;
        int             fYCount;
        const SkIRect*  fBounds;
        const SkColor*  fColors;
    };

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 SkCanvas::Lattice::RectType

            enum RectType : uint8_t {
                kDefault = 0,
                kTransparent,
                kFixedColor,
            };

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

Constants

const int* fXDivs

Array of x-coordinates 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.

const int* fYDivs

Array of y-coordinates 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.

const RectType* fRectTypes

Optional array of fill types, one per rectangular grid entry: array length must be( 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.

int fXCount

Number of entries in fXDivs array; one less than the number of horizontal divisions.

int fYCount

Number of entries in fYDivs array; one less than the number of vertical divisions.

const SkIRect* fBounds

Optional subset IRect source to draw from. If nullptr, source bounds is dimensions of Bitmap or Image.

const SkColor* fColors

Optional array of colors, one per rectangular grid entry. Array length must be( fXCount + 1) * (fYCount + 1) .

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

drawBitmapLattice

void drawBitmapLattice(const SkBitmap& bitmap, const Lattice& lattice, const SkRect& dst,
                       const SkPaint* paint = nullptr)

Draw 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.

Parameters

`SkCanvas::Lattice::kDefault`	0	Draws Bitmap into lattice rectangle.
`SkCanvas::Lattice::kTransparent`	1	Skips lattice rectangle by making it transparent.
`SkCanvas::Lattice::kFixedColor`	2	Draws one of fColors into lattice rectangle.

`bitmap`	Bitmap containing pixels, dimensions, and format
`lattice`	division of bitmap into fixed and variable rectangles
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr

Example

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.

drawImageLattice

void drawImageLattice(const SkImage* image, const Lattice& lattice, const SkRect& dst,
                      const SkPaint* paint = nullptr)

Draw 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.

Parameters

`image`	Image containing pixels, dimensions, and format
`lattice`	division of bitmap into fixed and variable rectangles
`dst`	destination Rect of image to draw to
`paint`	Paint containing Blend Mode, Color Filter, Image Filter, and so on; or nullptr

Example

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.

Draw Text

name	description
drawPosText	draws text at array of (x, y) positions
drawPosTextH	draws text at x positions with common baseline
drawString	draws null terminated string at (x, y) using font advance
	drawString(const char* string, SkScalar x, SkScalar y, const SkPaint& paint)
	drawString(const SkString& string, SkScalar x, SkScalar y, const SkPaint& paint)
drawText	draws text at (x, y), using font advance
drawTextBlob	draws text with arrays of positions and Paint
	drawTextBlob(const SkTextBlob* blob, SkScalar x, SkScalar y, const SkPaint& paint)
	drawTextBlob(const sk sp<SkTextBlob>& blob, SkScalar x, SkScalar y, const SkPaint& paint)
drawTextOnPath	draws text following Path contour
drawTextOnPathHV	draws text following Path with offsets
drawTextRSXform	draws text with array of RSXform

drawText

void drawText(const void* text, size_t byteLength, SkScalar x, SkScalar y, const SkPaint& paint)

Draw text, with origin at (x, y), using Clip, Matrix, and Paint paint.

text meaning depends on Paint Text Encoding; by default, text is encoded as UTF-8.

x and y meaning depends on Paint Text Align and Paint Vertical Text; by default text draws left to right, positioning the first glyph left side bearing at x and its baseline at y. Text size is affected by Matrix and Paint Text Size.

All elements of paint: Path Effect, Mask Filter, Shader, Color Filter, Image Filter, and Draw Looper; apply to text. By default, draws filled 12 point black Glyphs.

Parameters

`text`	character code points or Glyphs drawn
`byteLength`	byte length of text array
`x`	start of text on x-axis
`y`	start of text on y-axis
`paint`	text size, blend, color, and so on, used to draw

Example

The same text is drawn varying Paint Text Size and varying Matrix.

drawString

void drawString(const char* string, SkScalar x, SkScalar y, const SkPaint& paint)

Draw null terminated string, with origin at (x, y), using Clip, Matrix, and Paint paint. Note that this per-glyph xform does not affect the shader (if present) on the paint, just the glyph's geometry.

string meaning depends on Paint Text Encoding; by default, strings are encoded as UTF-8. Other values of Paint Text Encoding are unlikely to produce the desired results, since zero bytes may be embedded in the string.

x and y meaning depends on Paint Text Align and Paint Vertical Text; by default string draws left to right, positioning the first glyph left side bearing at x and its baseline at y. Text size is affected by Matrix and Paint Text Size.

All elements of paint: Path Effect, Mask Filter, Shader, Color Filter, Image Filter, and Draw Looper; apply to text. By default, draws filled 12 point black Glyphs.

Parameters

`string`	character code points or Glyphs drawn, ending with a char value of zero
`x`	start of string on x-axis
`y`	start of string on y-axis
`paint`	text size, blend, color, and so on, used to draw

Example

Parameters

`string`	character code points or Glyphs drawn, ending with a char value of zero
`x`	start of string on x-axis
`y`	start of string on y-axis
`paint`	text size, blend, color, and so on, used to draw

Example

drawPosText

void drawPosText(const void* text, size_t byteLength, const SkPoint pos[], const SkPaint& paint)

Draw each glyph in text with the origin in pos array, using Clip, Matrix, and Paint paint. The number of entries in pos array must match the number of Glyphs described by byteLength of text.

text meaning depends on Paint Text Encoding; by default, text is encoded as UTF-8. pos elements' meaning depends on Paint Text Align and Paint Vertical Text; by default each glyph left side bearing is positioned at x and its baseline is positioned at y. Text size is affected by Matrix and Paint Text Size.

All elements of paint: Path Effect, Mask Filter, Shader, Color Filter, Image Filter, and Draw Looper; apply to text. By default, draws filled 12 point black Glyphs.

Layout engines such as Harfbuzz typically position each glyph rather than using the font advance widths.

Parameters

`text`	character code points or Glyphs drawn
`byteLength`	byte length of text array
`pos`	array of glyph origins
`paint`	text size, blend, color, and so on, used to draw

Example

drawPosTextH

void drawPosTextH(const void* text, size_t byteLength, const SkScalar xpos[], SkScalar constY,
                  const SkPaint& paint)

Draw each glyph in text with its (x, y) origin composed from xpos array and constY, using Clip, Matrix, and Paint paint. The number of entries in xpos array must match the number of Glyphs described by byteLength of text.

text meaning depends on Paint Text Encoding; by default, text is encoded as UTF-8. xpos elements' meaning depends on Paint Text Align and Paint Vertical Text; by default each glyph left side bearing is positioned at an xpos element and its baseline is positioned at constY. Text size is affected by Matrix and Paint Text Size.

All elements of paint: Path Effect, Mask Filter, Shader, Color Filter, Image Filter, and Draw Looper; apply to text. By default, draws filled 12 point black Glyphs.

Layout engines such as Harfbuzz typically position each glyph rather than using the font advance widths if all Glyphs share the same baseline.

Parameters

`text`	character code points or Glyphs drawn
`byteLength`	byte length of text array
`xpos`	array of x positions, used to position each glyph
`constY`	shared y coordinate for all of x positions
`paint`	text size, blend, color, and so on, used to draw

Example

drawTextOnPathHV

void drawTextOnPathHV(const void* text, size_t byteLength, const SkPath& path, SkScalar hOffset,
                      SkScalar vOffset, const SkPaint& paint)

Draw text on Path path, using Clip, Matrix, and Paint paint.

Origin of text is at distance hOffset along the path, offset by a perpendicular vector of length vOffset. If the path section corresponding the glyph advance is curved, the glyph is drawn curved to match; control points in the glyph are mapped to projected points parallel to the path. If the text advance is larger than the path length, the excess text is clipped.

text meaning depends on Paint Text Encoding; by default, text is encoded as UTF-8. Origin meaning depends on Paint Text Align and Paint Vertical Text; by default text positions the first glyph left side bearing at origin x and its baseline at origin y. Text size is affected by Matrix and Paint Text Size.

All elements of paint: Path Effect, Mask Filter, Shader, Color Filter, Image Filter, and Draw Looper; apply to text. By default, draws filled 12 point black Glyphs.

Parameters

`text`	character code points or Glyphs drawn
`byteLength`	byte length of text array
`path`	Path providing text baseline
`hOffset`	distance along path to offset origin
`vOffset`	offset of text above (if negative) or below (if positive) the path
`paint`	text size, blend, color, and so on, used to draw

Example

drawTextOnPath

void drawTextOnPath(const void* text, size_t byteLength, const SkPath& path, const SkMatrix* matrix,
                    const SkPaint& paint)

Draw text on Path path, using Clip, Matrix, and Paint paint.

Origin of text is at beginning of path offset by matrix, if provided, before it is mapped to path. If the path section corresponding the glyph advance is curved, the glyph is drawn curved to match; control points in the glyph are mapped to projected points parallel to the path. If the text advance is larger than the path length, the excess text is clipped.

All elements of paint: Path Effect, Mask Filter, Shader, Color Filter, Image Filter, and Draw Looper; apply to text. By default, draws filled 12 point black Glyphs.

Parameters

`text`	character code points or Glyphs drawn
`byteLength`	byte length of text array
`path`	Path providing text baseline
`matrix`	transform of Glyphs before mapping to path; may be nullptr to use identity Matrix
`paint`	text size, blend, color, and so on, used to draw

Example

drawTextRSXform

void drawTextRSXform(const void* text, size_t byteLength, const SkRSXform xform[],
                     const SkRect* cullRect, const SkPaint& paint)

Draw text, transforming each glyph by the corresponding SkRSXform, using Clip, Matrix, and Paint paint.

RSXform array specifies a separate square scale, rotation, and translation for each glyph.

Optional Rect cullRect is a conservative bounds of text, taking into account RSXform and paint. If cullRect is outside of Clip, canvas can skip drawing.

All elements of paint: Path Effect, Mask Filter, Shader, Color Filter, Image Filter, and Draw Looper; apply to text. By default, draws filled 12 point black Glyphs.

Parameters

`text`	character code points or Glyphs drawn
`byteLength`	byte length of text array
`xform`	RSXform rotates, scales, and translates each glyph individually
`cullRect`	Rect bounds of text for efficient clipping; or nullptr
`paint`	text size, blend, color, and so on, used to draw

Example

drawTextBlob

void drawTextBlob(const SkTextBlob* blob, SkScalar x, SkScalar y, const SkPaint& paint)

Draw Text Blob blob at (x, y), using Clip, Matrix, and Paint paint.

blob contains Glyphs, their positions, and paint attributes specific to text: Typeface, Paint Text Size, Paint Text Scale X, Paint Text Skew X, Paint Text Align, Paint Hinting, Anti-alias, Paint Fake Bold, Font Embedded Bitmaps, Full Hinting Spacing, LCD Text, Linear Text, Subpixel Text, and Paint Vertical Text.

Paint Text Encoding must be set to SkPaint::kGlyphID TextEncoding.

Elements of paint: Path Effect, Mask Filter, Shader, Color Filter, Image Filter, and Draw Looper; apply to blob.

Parameters

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

Example

Parameters

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

Example

Paint attributes unrelated to text, like color, have no effect on paint in allocated Text Blob. Paint attributes related to text, like text size, have no effect on paint passed to drawTextBlob.

drawPicture

void drawPicture(const SkPicture* picture)

Draw Picture picture, using Clip and Matrix. Clip and Matrix are unchanged by picture contents, as if save was called before and restore was called after drawPicture.

Picture records a series of draw commands for later playback.

Parameters

picture recorded drawing commands to play

Example

Parameters

picture recorded drawing commands to play

Example

Parameters

`picture`	recorded drawing commands to play
`matrix`	Matrix to rotate, scale, translate, and so on; may be nullptr
`paint`	Paint to apply transparency, filtering, and so on; may be nullptr

Example

Parameters

`picture`	recorded drawing commands to play
`matrix`	Matrix to rotate, scale, translate, and so on; may be nullptr
`paint`	Paint to apply transparency, filtering, and so on; may be nullptr

Example

drawVertices

void drawVertices(const SkVertices* vertices, SkBlendMode mode, const SkPaint& paint)

Draw Vertices vertices, a triangle mesh, using Clip and Matrix. If Vertices Texs and Vertices Colors are defined in vertices, and Paint paint contains Shader, Blend Mode mode combines Vertices Colors with Shader.

Parameters

`vertices`	triangle mesh to draw
`mode`	combines Vertices Colors with Shader, if both are present
`paint`	specifies the Shader, used as Vertices texture; may be nullptr

Example

Parameters

`vertices`	triangle mesh to draw
`mode`	combines Vertices Colors with Shader, if both are present
`paint`	specifies the Shader, used as Vertices texture, may be nullptr

Example

drawPatch

void drawPatch(const SkPoint cubics[12], const SkColor colors[4], const SkPoint texCoords[4],
               SkBlendMode mode, const SkPaint& paint)

Draws a Coons_Patch: the interpolation of four cubics with shared corners, associating a color, and optionally a texture coordinate, with each corner.

Coons_Patch uses Clip and Matrix, paint Shader, Color Filter, Color Alpha, Image Filter, and Blend Mode. If Shader is provided it is treated as Coons_Patch texture; Blend Mode mode combines Color colors and Shader if both are provided.

Point array cubics specifies four Cubics starting at the top-left corner, in clockwise order, sharing every fourth point. The last Cubic ends at the first point.

Color array color associates colors with corners in top-left, top-right, bottom-right, bottom-left order.

If paint contains Shader, Point array texCoords maps Shader as texture to corners in top-left, top-right, bottom-right, bottom-left order.

Parameters

`cubics`	Path Cubic array, sharing common points
`colors`	Color array, one for each corner
`texCoords`	Point array of texture coordinates, mapping Shader to corners; may be nullptr
`mode`	Blend Mode for colors, and for Shader if paint has one
`paint`	Shader, Color Filter, Blend Mode, used to draw

Example

Parameters

`cubics`	Path Cubic array, sharing common points
`colors`	Color array, one for each corner
`texCoords`	Point array of texture coordinates, mapping Shader to corners; may be nullptr
`paint`	Shader, Color Filter, Blend Mode, used to draw

Example

drawAtlas

void drawAtlas(const SkImage* atlas, const SkRSXform xform[], const SkRect tex[],
               const SkColor colors[], int count, SkBlendMode mode, const SkRect* cullRect,
               const SkPaint* paint)

Draw a set of sprites from atlas, using Clip, Matrix, and optional Paint paint. paint uses Anti-alias, Color Alpha, Color Filter, Image Filter, and Blend Mode to draw, if present. For each entry in the array, Rect tex locates sprite in atlas, and RSXform xform transforms it into destination space.

xform, text, and colors if present, must contain count entries. Optional colors are applied for each sprite using Blend Mode. Optional cullRect is a conservative bounds of all transformed sprites. If cullRect is outside of Clip, canvas can skip drawing.

Parameters

`atlas`	Image containing sprites
`xform`	RSXform mappings for sprites in atlas
`tex`	Rect locations of sprites in atlas
`colors`	one per sprite, blended with sprite using Blend Mode; may be nullptr
`count`	number of sprites to draw
`mode`	Blend Mode combining colors and sprites
`cullRect`	bounds of transformed sprites for efficient clipping; may be nullptr
`paint`	Color Filter, Image Filter, Blend Mode, and so on; may be nullptr

Example

Parameters

`atlas`	Image containing sprites
`xform`	RSXform mappings for sprites in atlas
`tex`	Rect locations of sprites in atlas
`colors`	one per sprite, blended with sprite using Blend Mode; may be nullptr
`count`	number of sprites to draw
`mode`	Blend Mode combining colors and sprites
`cullRect`	bounds of transformed sprites for efficient clipping; may be nullptr
`paint`	Color Filter, Image Filter, Blend Mode, and so on; may be nullptr

Example

Parameters

`atlas`	Image containing sprites
`xform`	RSXform mappings for sprites in atlas
`tex`	Rect locations of sprites in atlas
`count`	number of sprites to draw
`cullRect`	bounds of transformed sprites for efficient clipping; may be nullptr
`paint`	Color Filter, Image Filter, Blend Mode, and so on; may be nullptr

Example

Parameters

`atlas`	Image containing sprites
`xform`	RSXform mappings for sprites in atlas
`tex`	Rect locations of sprites in atlas
`count`	number of sprites to draw
`cullRect`	bounds of transformed sprites for efficient clipping; may be nullptr
`paint`	Color Filter, Image Filter, Blend Mode, and so on; may be nullptr

Example

drawDrawable

void drawDrawable(SkDrawable* drawable, const SkMatrix* matrix = nullptr)

Draw Drawable drawable using Clip and Matrix, concatenated with optional matrix.

If Canvas has an asynchronous implementation, as is the case when it is recording into Picture, then drawable will be referenced, so that SkDrawable::draw() can be called when the operation is finalized. To force immediate drawing, call SkDrawable::draw() instead.

Parameters

`drawable`	custom struct encapsulating drawing commands
`matrix`	transformation applied to drawing; may be nullptr

Example

Parameters

`drawable`	custom struct encapsulating drawing commands
`x`	offset into Canvas writable pixels in x
`y`	offset into Canvas writable pixels in y

Example

drawAnnotation

void drawAnnotation(const SkRect& rect, const char key[], SkData* value)

Associate Rect on Canvas with an annotation; a key-value pair, where the key is a null-terminated utf8 string, and optional value is stored as Data.

Only some canvas implementations, such as recording to Picture, or drawing to Document PDF, use annotations.

Parameters

`rect`	Rect extent of canvas to annotate
`key`	string used for lookup
`value`	data holding value stored in annotation

Example

Parameters

`rect`	Rect extent of canvas to annotate
`key`	string used for lookup
`value`	data holding value stored in annotation

Example

getDrawFilter

SkDrawFilter* getDrawFilter() const

soon

setDrawFilter

virtual SkDrawFilter* setDrawFilter(SkDrawFilter* filter)

soon

isClipEmpty

virtual bool isClipEmpty() const

Returns true if Clip is empty; that is, nothing will draw.

May do work when called; it should not be called more often than needed. However, once called, subsequent calls perform no work until Clip changes.

Return Value

true if Clip is empty

Example

Example Output

clip is not empty
clip is empty

isClipRect

virtual bool isClipRect() const

Returns true if Clip is Rect and not empty. Returns false if the clip is empty, or if it is not Rect.

Return Value

true if Clip is Rect and not empty

Example

Example Output

clip is rect
clip is not rect

363 KiB Raw Blame History

SkCanvas Reference

Canvas

Overview

Overview Subtopic

Class SkCanvas

Related Function

Constant

Class or Struct

Constructor

Member Function

MakeRasterDirect

Parameters

Return Value

Example

Example Output

See Also

MakeRasterDirectN32

Parameters

Return Value

Example

Example Output

See Also

SkCanvas

Return Value

Example

Example Output

See Also

SkCanvas

Parameters

Return Value

Example

Example Output

See Also

SkCanvas

SkCanvas

Parameters

Return Value

Example

Example Output

See Also

Enum SkCanvas::ColorBehavior

Constants

SkCanvas

Parameters

Return Value

SkCanvas

Parameters

Return Value

Example

Example Output

See Also

~SkCanvas

Example

See Also

Property

getMetaData

Return Value

Example

Example Output

See Also

imageInfo

Return Value

Example

Example Output

See Also

getProps

Parameters

Return Value

Example

Example Output

See Also

Utility

flush

See Also

getBaseLayerSize

Return Value

Example

Example Output

See Also

363 KiB

Raw Blame History