skia2/docs/SkPicture_Reference.bmh

#Topic Picture
#Alias Pictures ##
#Alias Picture_Reference ##

#Class SkPicture

Picture records drawing commands made to Canvas. The command stream may be
played in whole or in part at a later time.

Picture is an abstract class. Picture may be generated by Picture_Recorder
or Drawable, or from Picture previously saved to Data or Stream. 

Picture may contain any Canvas drawing command, as well as one or more
Canvas_Matrix or Canvas_Clip. Picture has a cull Rect, which is used as
a bounding box hint. To limit Picture bounds, use Canvas_Clip when
recording or drawing Picture.

#Subtopic Overview
#Populate
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#Subtopic Class
#Populate
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#Subtopic Member_Function
#Populate
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# ------------------------------------------------------------------------------

#Class AbortCallback
#Line # utility to stop picture playback ##

#Code
    class AbortCallback {
    public:
        AbortCallback() {}
        virtual ~AbortCallback() {}
        virtual bool abort() = 0;
    };
##

AbortCallback is an abstract class. An implementation of AbortCallback may
passed as a parameter to SkPicture::playback, to stop it before all drawing
commands have been processed.

If AbortCallback::abort returns true, SkPicture::playback is interrupted.

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

#Method AbortCallback()
#In Constructor
#Line # defines default constructor ##
Has no effect.

#Return abstract class cannot be instantiated ##

#NoExample
##

#SeeAlso playback

#Method ##

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

#Method virtual ~AbortCallback()
#In Constructor
#Line # defines default destructor ##
Has no effect.

#NoExample
##

#SeeAlso playback

#Method ##

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

#Method virtual bool abort() = 0
#In Utility
#Line # aborts playback by callback ##

Stops Picture playback when some condition is met. A subclass of
AbortCallback provides an override for abort() that can stop SkPicture::playback.

The part of Picture drawn when aborted is undefined. Picture instantiations are
free to stop drawing at different points during playback.

If the abort happens inside one or more calls to SkCanvas::save(), stack
of Canvas_Matrix and Canvas_Clip values is restored to its state before
SkPicture::playback was called.

#Return true to stop playback ##

#NoExample
##

#SeeAlso playback

#Method ##

#Example
#Description
JustOneDraw allows the black rectangle to draw but stops playback before the
white rectangle appears.
##
#Function
class JustOneDraw : public SkPicture::AbortCallback {
public:
    bool abort() override { return fCalls++ > 0; }
private:
    int fCalls = 0;
};
##

void draw(SkCanvas* canvas) {
    SkPictureRecorder recorder;
    SkCanvas* pictureCanvas = recorder.beginRecording({0, 0, 256, 256});
    SkPaint paint;
    pictureCanvas->drawRect(SkRect::MakeWH(200, 200), paint);
    paint.setColor(SK_ColorWHITE);
    pictureCanvas->drawRect(SkRect::MakeLTRB(20, 20, 180, 180), paint);
    sk_sp<SkPicture> picture = recorder.finishRecordingAsPicture();
    JustOneDraw callback;
    picture->playback(canvas, &callback);
}

##

#Class AbortCallback ##

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

#Method static sk_sp<SkPicture> MakeFromStream(SkStream* stream,
                                           const SkDeserialProcs* procs = nullptr)
#In Constructor
#Line # constructs Picture from stream ##

Recreates Picture that was serialized into a stream. Returns constructed Picture
if successful; otherwise, returns nullptr. Fails if data does not permit
constructing valid Picture.

procs.fPictureProc permits supplying a custom function to decode Picture.
If procs.fPictureProc is nullptr, default decoding is used. procs.fPictureCtx
may be used to provide user context to procs.fPictureProc; procs.fPictureProc
is called with a pointer to data, data byte length, and user context.

#Param stream  container for serial data ##
#Param procs  custom serial data decoders; may be nullptr ##

#Return Picture constructed from stream data ##

#Example
    SkPictureRecorder recorder;
    SkCanvas* pictureCanvas = recorder.beginRecording({0, 0, 256, 256});
    SkPaint paint;
    pictureCanvas->drawRect(SkRect::MakeWH(200, 200), paint);
    paint.setColor(SK_ColorWHITE);
    pictureCanvas->drawRect(SkRect::MakeLTRB(20, 20, 180, 180), paint);
    sk_sp<SkPicture> picture = recorder.finishRecordingAsPicture();
    SkDynamicMemoryWStream writableStream;
    picture->serialize(&writableStream);
    std::unique_ptr<SkStreamAsset> readableStream = writableStream.detachAsStream();
    sk_sp<SkPicture> copy = SkPicture::MakeFromStream(readableStream.get());
    copy->playback(canvas);
##

#SeeAlso MakeFromData SkPictureRecorder

#Method ##

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

#Method static sk_sp<SkPicture> MakeFromData(const SkData* data,
                                         const SkDeserialProcs* procs = nullptr)
#In Constructor
#Line # constructs Picture from data ##

Recreates Picture that was serialized into data. Returns constructed Picture
if successful; otherwise, returns nullptr. Fails if data does not permit
constructing valid Picture.

procs.fPictureProc permits supplying a custom function to decode Picture.
If procs.fPictureProc is nullptr, default decoding is used. procs.fPictureCtx
may be used to provide user context to procs.fPictureProc; procs.fPictureProc
is called with a pointer to data, data byte length, and user context.

#Param data  container for serial data ##
#Param procs  custom serial data decoders; may be nullptr ##

#Return Picture constructed from data ##

#Example
    SkPictureRecorder recorder;
    SkCanvas* pictureCanvas = recorder.beginRecording({0, 0, 256, 256});
    SkPaint paint;
    pictureCanvas->drawRect(SkRect::MakeWH(200, 200), paint);
    paint.setColor(SK_ColorWHITE);
    pictureCanvas->drawRect(SkRect::MakeLTRB(20, 20, 180, 180), paint);
    sk_sp<SkPicture> picture = recorder.finishRecordingAsPicture();
    SkDynamicMemoryWStream writableStream;
    picture->serialize(&writableStream);
    sk_sp<SkData> readableData = writableStream.detachAsData();
    sk_sp<SkPicture> copy = SkPicture::MakeFromData(readableData.get());
    copy->playback(canvas);
##

#SeeAlso MakeFromStream SkPictureRecorder

#Method ##

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

#Method static sk_sp<SkPicture> MakeFromData(const void* data, size_t size,
                                         const SkDeserialProcs* procs = nullptr)

#Param data  pointer to serial data ##
#Param size  size of data ##
#Param procs  custom serial data decoders; may be nullptr ##

Recreates Picture that was serialized into data. Returns constructed Picture
if successful; otherwise, returns nullptr. Fails if size is smaller than
required data length, or if data does not permit constructing valid Picture.

procs.fPictureProc permits supplying a custom function to decode Picture.
If procs.fPictureProc is nullptr, default decoding is used. procs.fPictureCtx
may be used to provide user context to procs.fPictureProc; procs.fPictureProc
is called with a pointer to data, data byte length, and user context.

#Return Picture constructed from data ##

#Example
    SkPictureRecorder recorder;
    SkCanvas* pictureCanvas = recorder.beginRecording({0, 0, 256, 256});
    SkPaint paint;
    pictureCanvas->drawRect(SkRect::MakeWH(200, 200), paint);
    paint.setColor(SK_ColorWHITE);
    pictureCanvas->drawRect(SkRect::MakeLTRB(20, 20, 180, 180), paint);
    sk_sp<SkPicture> picture = recorder.finishRecordingAsPicture();
    SkDynamicMemoryWStream writableStream;
    picture->serialize(&writableStream);
    sk_sp<SkData> readableData = writableStream.detachAsData();
    sk_sp<SkPicture> copy = SkPicture::MakeFromData(readableData->data(), readableData->size());
    copy->playback(canvas);
##

#SeeAlso MakeFromStream SkPictureRecorder

#Method ##

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

#Method virtual void playback(SkCanvas* canvas, AbortCallback* callback = nullptr) const = 0
#In Action
#Line # replays drawing commands on canvas ##

Replays the drawing commands on the specified canvas. In the case that the
commands are recorded, each command in the Picture is sent separately to canvas.

To add a single command to draw Picture to recording canvas, call
SkCanvas::drawPicture instead.

#Param canvas  receiver of drawing commands ##
#Param callback  allows interruption of playback ##

#Example
    SkPictureRecorder recorder;
    SkCanvas* pictureCanvas = recorder.beginRecording({0, 0, 256, 256});
    SkPaint paint;
    pictureCanvas->drawRect(SkRect::MakeWH(200, 200), paint);
    paint.setColor(SK_ColorWHITE);
    pictureCanvas->drawRect(SkRect::MakeLTRB(20, 20, 180, 180), paint);
    sk_sp<SkPicture> picture = recorder.finishRecordingAsPicture();
    picture->playback(canvas);
##

#SeeAlso SkCanvas::drawPicture

#Method ##

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

#Method virtual SkRect cullRect() const = 0
#In Property
#Line # returns bounds used to record Picture ##

Returns cull Rect for this picture, passed in when Picture was created.
Returned Rect does not specify clipping Rect for Picture; cull is hint
of Picture bounds.

Picture is free to discard recorded drawing commands that fall outside 
cull.

#Return bounds passed when Picture was created ##

#Example
#Description
Picture recorded bounds are smaller than contents; contents outside recorded
bounds may be drawn, and are drawn in this example.
##
    SkPictureRecorder recorder;
    SkCanvas* pictureCanvas = recorder.beginRecording({64, 64, 192, 192});
    SkPaint paint;
    pictureCanvas->drawRect(SkRect::MakeWH(200, 200), paint);
    paint.setColor(SK_ColorWHITE);
    pictureCanvas->drawRect(SkRect::MakeLTRB(20, 20, 180, 180), paint);
    sk_sp<SkPicture> picture = recorder.finishRecordingAsPicture();
    picture->playback(canvas);
    paint.setBlendMode(SkBlendMode::kModulate);
    paint.setColor(0x40404040);
    canvas->drawRect(picture->cullRect(), paint);
##

#SeeAlso SkCanvas::clipRect

#Method ##

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

#Method uint32_t uniqueID() const
#In Property
#Line # returns identifier for Picture ##

Returns a non-zero value unique among Pictures in Skia process.

#Return identifier for Picture ##

#Example
    SkPictureRecorder recorder;
    recorder.beginRecording({0, 0, 0, 0});
    sk_sp<SkPicture> picture = recorder.finishRecordingAsPicture();
    SkDebugf("empty picture id = %d\n", picture->uniqueID());
    sk_sp<SkPicture> placeholder = SkPicture::MakePlaceholder({0, 0, 0, 0});
    SkDebugf("placeholder id = %d\n", placeholder->uniqueID());
#StdOut
empty picture id = 1
placeholder id = 2
##
##

#SeeAlso SkRefCnt

#Method ##

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

#Method sk_sp<SkData> serialize(const SkSerialProcs* procs = nullptr) const
#In Utility
#Line # writes Picture to Data ##
Returns storage containing Data describing Picture, using optional custom
encoders.

procs.fPictureProc permits supplying a custom function to encode Picture.
If procs.fPictureProc is nullptr, default encoding is used. procs.fPictureCtx
may be used to provide user context to procs.fPictureProc; procs.fPictureProc
is called with a pointer to Picture and user context.

#Param procs  custom serial data encoders; may be nullptr ##

#Return storage containing serialized Picture ##

#Example
    SkPictureRecorder recorder;
    SkCanvas* pictureCanvas = recorder.beginRecording({0, 0, 256, 256});
    SkPaint paint;
    pictureCanvas->drawRect(SkRect::MakeWH(200, 200), paint);
    paint.setColor(SK_ColorWHITE);
    pictureCanvas->drawRect(SkRect::MakeLTRB(20, 20, 180, 180), paint);
    sk_sp<SkPicture> picture = recorder.finishRecordingAsPicture();
    sk_sp<SkData> readableData = picture->serialize();
    sk_sp<SkPicture> copy = SkPicture::MakeFromData(readableData->data(), readableData->size());
    copy->playback(canvas);
##

#SeeAlso MakeFromData SkData SkSerialProcs

#Method ##

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

#Method void serialize(SkWStream* stream, const SkSerialProcs* procs = nullptr) const
Writes picture to stream, using optional custom encoders.

procs.fPictureProc permits supplying a custom function to encode Picture.
If procs.fPictureProc is nullptr, default encoding is used. procs.fPictureCtx
may be used to provide user context to procs.fPictureProc; procs.fPictureProc
is called with a pointer to Picture and user context.

#Param stream  writable serial data stream ##
#Param procs  custom serial data encoders; may be nullptr ##

#Example
    SkPictureRecorder recorder;
    SkCanvas* pictureCanvas = recorder.beginRecording({0, 0, 256, 256});
    SkPaint paint;
    pictureCanvas->drawRect(SkRect::MakeWH(200, 200), paint);
    paint.setColor(SK_ColorWHITE);
    pictureCanvas->drawRect(SkRect::MakeLTRB(20, 20, 180, 180), paint);
    sk_sp<SkPicture> picture = recorder.finishRecordingAsPicture();
    SkDynamicMemoryWStream writableStream;
    picture->serialize(&writableStream);
    sk_sp<SkData> readableData = writableStream.detachAsData();
    sk_sp<SkPicture> copy = SkPicture::MakeFromData(readableData->data(), readableData->size());
    copy->playback(canvas);
##

#SeeAlso MakeFromStream SkWStream SkSerialProcs

#Method ##

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

#Method static sk_sp<SkPicture> MakePlaceholder(SkRect cull)
#In Constructor
#Line # constructs placeholder with unique identifier ##

Returns a placeholder SkPicture. Result does not draw, and contains only
cull Rect, a hint of its bounds. Result is immutable; it cannot be changed
later. Result identifier is unique.

Returned placeholder can be intercepted during playback to insert other
commands into Canvas draw stream.

#Param cull  placeholder dimensions
##

#Return placeholder with unique identifier ##

#Example
#Function
class MyCanvas : public SkCanvas {
public:
    MyCanvas(SkCanvas* c) : canvas(c) {}
        void onDrawPicture(const SkPicture* picture, const SkMatrix* ,
                               const SkPaint* ) override {
        const SkRect rect = picture->cullRect();
        SkPaint redPaint;
        redPaint.setColor(SK_ColorRED);
        canvas->drawRect(rect, redPaint);
   }

   SkCanvas* canvas;
};
##
SkPictureRecorder recorder;
SkCanvas* pictureCanvas = recorder.beginRecording({0, 0, 256, 256});
sk_sp<SkPicture> placeholder = SkPicture::MakePlaceholder({10, 40, 80, 110});
pictureCanvas->drawPicture(placeholder);
sk_sp<SkPicture> picture = recorder.finishRecordingAsPicture();
MyCanvas myCanvas(canvas);
myCanvas.drawPicture(picture);
##

#SeeAlso MakeFromStream MakeFromData uniqueID

#Method ##

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

#Method virtual int approximateOpCount() const = 0
#In Property
#Line # returns approximate operation count ##

Returns the approximate number of operations in Picture. Returned value
may be greater or less than the number of SkCanvas calls
recorded: some calls may be recorded as more than one operation, other
calls may be optimized away.

#Return approximate operation count ##

#Example
    SkPictureRecorder recorder;
    SkCanvas* pictureCanvas = recorder.beginRecording({0, 0, 256, 256});
    SkPaint paint;
    pictureCanvas->drawRect(SkRect::MakeWH(200, 200), paint);
    paint.setColor(SK_ColorWHITE);
    pictureCanvas->drawRect(SkRect::MakeLTRB(20, 20, 180, 180), paint);
    sk_sp<SkPicture> picture = recorder.finishRecordingAsPicture();
    picture->playback(canvas);
    std::string opCount = "approximate op count: " + std::to_string(picture->approximateOpCount());
    canvas->drawString(opCount.c_str(), 50, 220, SkPaint());
##

#SeeAlso approximateBytesUsed

#Method ##

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

#Method virtual size_t approximateBytesUsed() const = 0
#In Property
#Line # returns approximate size ##

Returns the approximate byte size of Picture. Does not include large objects
referenced by Picture.

#Return approximate size ##

#Example
    SkPictureRecorder recorder;
    SkCanvas* pictureCanvas = recorder.beginRecording({0, 0, 256, 256});
    SkPaint paint;
    pictureCanvas->drawRect(SkRect::MakeWH(200, 200), paint);
    paint.setColor(SK_ColorWHITE);
    pictureCanvas->drawRect(SkRect::MakeLTRB(20, 20, 180, 180), paint);
    sk_sp<SkPicture> picture = recorder.finishRecordingAsPicture();
    picture->playback(canvas);
    std::string opCount = "approximate bytes used: " + std::to_string(picture->approximateBytesUsed());
    canvas->drawString(opCount.c_str(), 20, 220, SkPaint());
##

#SeeAlso approximateOpCount

#Method ##

#Class SkPicture ##

#Topic Picture ##