path: root/docs/SkSurface_Reference.bmh

#Topic Surface
#Alias Surface_Reference

#Class SkSurface

SkSurface is responsible for managing the pixels that a canvas draws into. The pixels can be
allocated either in CPU memory (a raster surface) or on the GPU (a GrRenderTarget surface).
SkSurface takes care of allocating a SkCanvas that will draw into the surface. Call
surface->getCanvas() to use that canvas (but don't delete it, it is owned by the surface).
SkSurface always has non-zero dimensions. If there is a request for a new surface, and either
of the requested dimensions are zero, then nullptr will be returned.

#Topic Overview

#Subtopic Subtopics
#ToDo manually add subtopics ##
#Table
#Legend
# topics # description ##
#Legend ##
#Table ##
##

#Subtopic Member_Functions
#Table
#Legend
# description                          # function ##
#Legend ##
# MakeFromBackendRenderTarget          # Creates Surface from GPU memory buffer. ##
# MakeFromBackendTexture               # Creates Surface from GPU-backed texture. ##
# MakeFromBackendTextureAsRenderTarget # Creates Surface from GPU-backed texture. ##
# MakeNull                             # Creates Surface without backing pixels. ##
# MakeRaster                           # Creates Surface from SkImageInfo. ##
# MakeRasterDirect                     # Creates Surface from SkImageInfo and Pixel_Storage. ##
# MakeRasterDirectReleaseProc          # Creates Surface from SkImageInfo and Pixel_Storage. ##
# MakeRasterN32Premul                  # Creates Surface from width, height matching output. ##
# MakeRenderTarget                     # Creates Surface pointing to new GPU memory buffer. ##
# characterize()                       # Set up Surface_Characterization for threaded pre-processing. ##
# draw()                               # Draws Surface contents to canvas. ##
# flush()                              # Resolve pending I/O. ##
# flushAndSignalSemaphores             # Resolve pending I/O, and signal. ##
# generationID                         # Returns unique ID. ##
# getCanvas                            # Returns Canvas that draws into Surface. ##
# getRenderTargetHandle                # Returns the GPU reference to render target. ##
# getTextureHandle                     # Returns the GPU reference to texture. ##
# height()                             # Returns pixel row count. ##
# makeImageSnapshot                    # Returns Image capturing Surface contents. ##
# makeSurface                          # Returns a compatible Surface. ##
# notifyContentWillChange              # Notifies that contents will be changed outside of Skia. ##
# peekPixels                           # Copies Surface parameters to Pixmap. ##
# prepareForExternalIO                 # To be deprecated. ##
# props()                              # Returns Surface_Properties. ##
# readPixels                           # Copies Rect of pixels. ##
# wait()                               # Pause commands until signaled. ##
# width()                              # Returns pixel column count. ##
#Table ##
#Subtopic ##

#Topic ##

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

#Method static sk_sp<SkSurface> MakeRasterDirect(const SkImageInfo& imageInfo, void* pixels,
                                             size_t rowBytes,
                                             const SkSurfaceProps* surfaceProps = nullptr)

Allocates raster Surface. Canvas returned by Surface draws directly into pixels.

Surface is returned if all parameters are valid.
Valid parameters include:
info dimensions are greater than zero;
info contains Image_Color_Type and Image_Alpha_Type supported by Raster_Surface;
pixels is not nullptr;
rowBytes is large enough to contain info width pixels of Image_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.

#Param imageInfo  width, height, Image_Color_Type, Image_Alpha_Type, Color_Space,
                  of Raster_Surface; width and height must be greater than zero
##
#Param pixels  pointer to destination pixels buffer ##
#Param rowBytes  interval from one Surface row to the next ##
#Param surfaceProps  LCD striping orientation and setting for device independent fonts;
              may be nullptr
##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#Example
void draw(SkCanvas* ) {
    SkImageInfo info = SkImageInfo::MakeN32Premul(3, 3);
    const size_t size = info.computeMinByteSize();
    SkAutoTMalloc<SkPMColor> storage(size);
    SkPMColor* pixels = storage.get();
    sk_sp<SkSurface> surface(SkSurface::MakeRasterDirect(info, pixels, info.minRowBytes()));
    SkCanvas* canvas = surface->getCanvas();
    canvas->clear(SK_ColorWHITE);
    SkPMColor pmWhite = pixels[0];
    SkPaint paint;
    canvas->drawPoint(1, 1, paint);
    canvas->flush();  // ensure that point was drawn
    for (int y = 0; y < info.height(); ++y) {
        for (int x = 0; x < info.width(); ++x) {
            SkDebugf("%c", *pixels++ == pmWhite ? '-' : 'x');
        }
        SkDebugf("\n");
    }
}
    #StdOut
        ---
        -x-
        ---
    ##
##

#SeeAlso MakeRasterDirectReleaseProc MakeRaster MakeRasterN32Premul SkCanvas::MakeRasterDirect

#Method ##

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

#Method static sk_sp<SkSurface> MakeRasterDirectReleaseProc(const SkImageInfo& imageInfo, void* pixels,
                                    size_t rowBytes,
                                    void (*releaseProc)(void* pixels, void* context),
                                    void* context, const SkSurfaceProps* surfaceProps = nullptr)

Allocates raster Surface. Canvas returned by Surface draws directly into pixels.
releaseProc is called with pixels and context when Surface is deleted.

Surface is returned if all parameters are valid.
Valid parameters include:
info dimensions are greater than zero;
info contains Image_Color_Type and Image_Alpha_Type supported by Raster_Surface;
pixels is not nullptr;
rowBytes is large enough to contain info width pixels of Image_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.

#Param imageInfo  width, height, Image_Color_Type, Image_Alpha_Type, Color_Space,
                  of Raster_Surface; width and height must be greater than zero
##
#Param pixels  pointer to destination pixels buffer ##
#Param rowBytes  interval from one Surface row to the next ##
#Param releaseProc  called when Surface is deleted; may be nullptr ##
#Param context  passed to releaseProc; may be nullptr ##
#Param surfaceProps  LCD striping orientation and setting for device independent fonts;
              may be nullptr
##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#Example
#Function
static void release_direct_surface_storage(void* pixels, void* context) {
    if (pixels == context) {
        SkDebugf("expected release context\n");
    }
    sk_free(pixels);
}

##
void draw(SkCanvas* ) {
    SkImageInfo info = SkImageInfo::MakeN32Premul(3, 3);
    const size_t rowBytes = info.minRowBytes();
    void* pixels = sk_malloc_throw(info.computeByteSize(rowBytes));
    sk_sp<SkSurface> surface(SkSurface::MakeRasterDirectReleaseProc(info, pixels, rowBytes,
            release_direct_surface_storage, pixels));
    SkCanvas* canvas = surface->getCanvas();
    canvas->clear(SK_ColorWHITE);
    SkPMColor* colorPtr = (SkPMColor*) pixels;
    SkPMColor pmWhite = colorPtr[0];
    SkPaint paint;
    canvas->drawPoint(1, 1, paint);
    canvas->flush();  // ensure that point was drawn
    for (int y = 0; y < info.height(); ++y) {
        for (int x = 0; x < info.width(); ++x) {
            SkDebugf("%c", *colorPtr++ == pmWhite ? '-' : 'x');
        }
        SkDebugf("\n");
    }
}
#StdOut
---
-x-
---
expected release context
##
##

#SeeAlso MakeRasterDirect MakeRasterN32Premul MakeRaster

#Method ##

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

#Method static sk_sp<SkSurface> MakeRaster(const SkImageInfo& imageInfo, size_t rowBytes,
                                       const SkSurfaceProps* surfaceProps)

Allocates raster Surface. Canvas returned by Surface draws directly into pixels.
Allocates and zeroes pixel memory. Pixel memory size is imageInfo.height() times
rowBytes, or times imageInfo.minRowBytes() if rowBytes is zero.
Pixel memory is deleted when Surface is deleted.

Surface is returned if all parameters are valid.
Valid parameters include:
info dimensions are greater than zero;
info contains Image_Color_Type and Image_Alpha_Type supported by Raster_Surface;
rowBytes is large enough to contain info width pixels of Image_Color_Type, or is zero.

If rowBytes is not zero, subsequent images returned by makeImageSnapshot
have the same rowBytes.

#Param imageInfo  width, height, Image_Color_Type, Image_Alpha_Type, Color_Space,
                  of Raster_Surface; width and height must be greater than zero
##
#Param rowBytes  interval from one Surface row to the next; may be zero ##
#Param surfaceProps  LCD striping orientation and setting for device independent fonts;
              may be nullptr
##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#Example
void draw(SkCanvas* ) {
    SkImageInfo info = SkImageInfo::MakeN32Premul(3, 3);
    const size_t rowBytes = 64;
    sk_sp<SkSurface> surface(SkSurface::MakeRaster(info, rowBytes, nullptr));
    SkCanvas* canvas = surface->getCanvas();
    canvas->clear(SK_ColorWHITE);
    SkPixmap pixmap;
    if (surface->peekPixels(&pixmap)) {
        const uint32_t* colorPtr = pixmap.addr32();
        SkPMColor pmWhite = colorPtr[0];
        SkPaint paint;
        canvas->drawPoint(1, 1, paint);
        canvas->flush();  // ensure that point was drawn
        for (int y = 0; y < info.height(); ++y) {
            for (int x = 0; x < info.width(); ++x) {
                SkDebugf("%c", colorPtr[x] == pmWhite ? '-' : 'x');
            }
            colorPtr += rowBytes / sizeof(colorPtr[0]);
            SkDebugf("\n");
        }
    }
}
#StdOut
---
-x-
---
##
##

#SeeAlso MakeRasterDirect MakeRasterN32Premul MakeRasterDirectReleaseProc

#Method ##

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

#Method static sk_sp<SkSurface> MakeRaster(const SkImageInfo& imageInfo,
                                       const SkSurfaceProps* props = nullptr)

Allocates raster Surface. Canvas returned by Surface draws directly into pixels.
Allocates and zeroes pixel memory. Pixel memory size is imageInfo.height() times
imageInfo.minRowBytes().
Pixel memory is deleted when Surface is deleted.

Surface is returned if all parameters are valid.
Valid parameters include:
info dimensions are greater than zero;
info contains Image_Color_Type and Image_Alpha_Type supported by Raster_Surface.

#Param imageInfo  width, height, Image_Color_Type, Image_Alpha_Type, Color_Space,
                  of Raster_Surface; width and height must be greater than zero
##
#Param props  LCD striping orientation and setting for device independent fonts;
              may be nullptr
##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#Example
void draw(SkCanvas* ) {
    SkImageInfo info = SkImageInfo::MakeN32Premul(3, 3);
    sk_sp<SkSurface> surface(SkSurface::MakeRaster(info));
    SkCanvas* canvas = surface->getCanvas();
    canvas->clear(SK_ColorWHITE);
    SkPixmap pixmap;
    if (surface->peekPixels(&pixmap)) {
        const uint32_t* colorPtr = pixmap.addr32();
        SkPMColor pmWhite = colorPtr[0];
        SkPaint paint;
        canvas->drawPoint(1, 1, paint);
        canvas->flush();  // ensure that point was drawn
        for (int y = 0; y < info.height(); ++y) {
            for (int x = 0; x < info.width(); ++x) {
                SkDebugf("%c", colorPtr[x] == pmWhite ? '-' : 'x');
            }
            colorPtr += info.width();
            SkDebugf("\n");
        }
    }
}
##

#SeeAlso MakeRasterDirect MakeRasterN32Premul MakeRasterDirectReleaseProc

#Method ##

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

#Method static sk_sp<SkSurface> MakeRasterN32Premul(int width, int height,
                                                const SkSurfaceProps* surfaceProps = nullptr)

Allocates raster Surface. Canvas returned by Surface draws directly into pixels.
Allocates and zeroes pixel memory. Pixel memory size is height times width times
four. Pixel memory is deleted when Surface is deleted.

Internally, sets Image_Info to width, height, Native_Color_Type, and
kPremul_SkAlphaType.

Surface is returned if width and height are greater than zero.

Use to create Surface that matches SkPMColor, the native pixel arrangement on
the platform. Surface drawn to output device skips converting its pixel format.

#Param width  pixel column count; must be greater than zero ##
#Param height  pixel row count; must be greater than zero ##
#Param surfaceProps  LCD striping orientation and setting for device independent
                     fonts; may be nullptr
##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#Example
void draw(SkCanvas* ) {
    sk_sp<SkSurface> surface(SkSurface::MakeRasterN32Premul(3, 3));
    SkCanvas* canvas = surface->getCanvas();
    canvas->clear(SK_ColorWHITE);
    SkPixmap pixmap;
    if (surface->peekPixels(&pixmap)) {
        const uint32_t* colorPtr = pixmap.addr32();
        SkPMColor pmWhite = colorPtr[0];
        SkPaint paint;
        canvas->drawPoint(1, 1, paint);
        canvas->flush();  // ensure that point was drawn
        for (int y = 0; y < surface->height(); ++y) {
            for (int x = 0; x < surface->width(); ++x) {
                SkDebugf("%c", colorPtr[x] == pmWhite ? '-' : 'x');
            }
            colorPtr += surface->width();
            SkDebugf("\n");
        }
    }
}
#StdOut
---
-x-
---
##
##

#SeeAlso MakeRasterDirect MakeRasterN32Premul MakeRasterDirectReleaseProc

#Method ##

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

#Method static sk_sp<SkSurface> MakeFromBackendTexture(GrContext* context,
                                                   const GrBackendTexture& backendTexture,
                                                   GrSurfaceOrigin origin, int sampleCnt,
                                                   sk_sp<SkColorSpace> colorSpace,
                                                   const SkSurfaceProps* surfaceProps)

Wraps a GPU-backed texture into Surface. Caller must ensure the texture is
valid for the lifetime of returned Surface. If sampleCnt greater than zero,
creates an intermediate MSAA Surface which is used for drawing backendTexture.

Surface is returned if all parameters are valid. backendTexture is valid if
its pixel configuration agrees with colorSpace and context; for instance, if
backendTexture has an sRGB configuration, then context must support sRGB,
and colorSpace must be present. Further, backendTexture width and height must
not exceed context capabilities, and the context must be able to support
back-end textures.

If SK_SUPPORT_GPU is defined as zero, has no effect and returns nullptr.

#Param context  GPU_Context ##
#Param backendTexture  texture residing on GPU ##
#Param origin   one of: kBottomLeft_GrSurfaceOrigin, kTopLeft_GrSurfaceOrigin ##
#Param sampleCnt  samples per pixel, or 0 to disable full scene anti-aliasing ##
#Param colorSpace  range of colors ##
#Param surfaceProps  LCD striping orientation and setting for device independent
                     fonts; may be nullptr
##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#Example
#ToDo  remove !fiddle below once backEndTextureRenderTarget is available ##
#Platform !fiddle gpu cpu
    SkPaint paint;
    paint.setTextSize(32);
    GrContext* context = canvas->getGrContext();
    if (!context) {
         canvas->drawString("GPU only!", 20, 40, paint);
         return;
    }
    sk_sp<SkSurface> gpuSurface = SkSurface::MakeFromBackendTexture(context,
            backEndTextureRenderTarget, kTopLeft_GrSurfaceOrigin, 0, nullptr, nullptr);
    auto surfaceCanvas = gpuSurface->getCanvas();
    surfaceCanvas->clear(SK_ColorWHITE);
    surfaceCanvas->drawString("GPU rocks!", 20, 40, paint);
    sk_sp<SkImage> image(gpuSurface->makeImageSnapshot());
    canvas->drawImage(image, 0, 0);
##

#SeeAlso GrBackendTexture MakeFromBackendRenderTarget MakeRenderTarget

#Method ##

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

#Method static sk_sp<SkSurface> MakeFromBackendTexture(GrContext* context,
                                                   const GrBackendTexture& backendTexture,
                                                   GrSurfaceOrigin origin, int sampleCnt,
                                                   SkColorType colorType,
                                                   sk_sp<SkColorSpace> colorSpace,
                                                   const SkSurfaceProps* surfaceProps)

Wraps a GPU-backed texture into Surface. Caller must ensure the texture is
valid for the lifetime of returned Surface. If sampleCnt greater than zero,
creates an intermediate MSAA Surface which is used for drawing backendTexture.

Surface is returned if all parameters are valid. backendTexture is valid if
its pixel configuration agrees with colorSpace and context; for instance, if
backendTexture has an sRGB configuration, then context must support sRGB,
and colorSpace must be present. Further, backendTexture width and height must
not exceed context capabilities, and the context must be able to support
back-end textures.

If SK_SUPPORT_GPU is defined as zero, has no effect and returns nullptr.

#Param context  GPU_Context ##
#Param backendTexture  texture residing on GPU ##
#Param origin   one of: kBottomLeft_GrSurfaceOrigin, kTopLeft_GrSurfaceOrigin ##
#Param sampleCnt  samples per pixel, or 0 to disable full scene anti-aliasing ##
#Param colorType  one of: kUnknown_SkColorType, kAlpha_8_SkColorType,
                          kRGB_565_SkColorType, kARGB_4444_SkColorType,
                          kRGBA_8888_SkColorType, kBGRA_8888_SkColorType,
                          kGray_8_SkColorType, kRGBA_F16_SkColorType
##
#Param colorSpace  range of colors ##
#Param surfaceProps  LCD striping orientation and setting for device independent
                     fonts; may be nullptr
##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#Example
#ToDo  remove !fiddle below once backEndTextureRenderTarget is available ##
#Platform !fiddle gpu cpu
    SkPaint paint;
    paint.setTextSize(32);
    GrContext* context = canvas->getGrContext();
    if (!context) {
         canvas->drawString("GPU only!", 20, 40, paint);
         return;
    }
    sk_sp<SkSurface> gpuSurface = SkSurface::MakeFromBackendTexture(context,
            backEndTextureRenderTarget, kTopLeft_GrSurfaceOrigin,
            kRGBA_8888_SkColorType, 0, nullptr, nullptr);
    auto surfaceCanvas = gpuSurface->getCanvas();
    surfaceCanvas->clear(SK_ColorWHITE);
    surfaceCanvas->drawString("GPU rocks!", 20, 40, paint);
    sk_sp<SkImage> image(gpuSurface->makeImageSnapshot());
    canvas->drawImage(image, 0, 0);
##

#SeeAlso GrBackendTexture MakeFromBackendRenderTarget MakeRenderTarget

#Method ##

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

#Method static sk_sp<SkSurface> MakeFromBackendRenderTarget(GrContext* context,
                                                const GrBackendRenderTarget& backendRenderTarget,
                                                GrSurfaceOrigin origin,
                                                sk_sp<SkColorSpace> colorSpace,
                                                const SkSurfaceProps* surfaceProps)

Wraps a GPU-backed buffer into Surface. Caller must ensure render target is
valid for the lifetime of returned Surface.

Surface is returned if all parameters are valid. backendRenderTarget is valid if
its pixel configuration agrees with colorSpace and context; for instance, if
backendRenderTarget has an sRGB configuration, then context must support sRGB,
and colorSpace must be present. Further, backendRenderTarget width and height must
not exceed context capabilities, and the context must be able to support
back-end render targets.

If SK_SUPPORT_GPU is defined as zero, has no effect and returns nullptr.

#Param context  GPU_Context ##
#Param backendRenderTarget  GPU intermediate memory buffer ##
#Param origin   one of: kBottomLeft_GrSurfaceOrigin, kTopLeft_GrSurfaceOrigin ##
#Param colorSpace  range of colors ##
#Param surfaceProps  LCD striping orientation and setting for device independent
                     fonts; may be nullptr
##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#Example
#ToDo  remove !fiddle below once backEndTextureRenderTarget is available ##
#Platform !fiddle gpu
    SkPaint paint;
    paint.setTextSize(32);
    GrContext* context = canvas->getGrContext();
    if (!context) {
         canvas->drawString("GPU only!", 20, 40, paint);
         return;
    }
    sk_sp<SkSurface> gpuSurface = SkSurface::MakeFromBackendRenderTarget(context,
            backEndRenderTarget, kTopLeft_GrSurfaceOrigin, nullptr, nullptr);
    auto surfaceCanvas = gpuSurface->getCanvas();
    surfaceCanvas->clear(SK_ColorWHITE);
    surfaceCanvas->drawString("GPU rocks!", 20, 40, paint);
    sk_sp<SkImage> image(gpuSurface->makeImageSnapshot());
    canvas->drawImage(image, 0, 0);
##

#SeeAlso MakeFromBackendTexture MakeRenderTarget

#Method ##

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

#Method static sk_sp<SkSurface> MakeFromBackendRenderTarget(GrContext* context,
                                                const GrBackendRenderTarget& backendRenderTarget,
                                                GrSurfaceOrigin origin,
                                                SkColorType colorType,
                                                sk_sp<SkColorSpace> colorSpace,
                                                const SkSurfaceProps* surfaceProps)

Wraps a GPU-backed buffer into Surface. Caller must ensure render target is
valid for the lifetime of returned Surface.

Surface is returned if all parameters are valid. backendRenderTarget is valid if
its pixel configuration agrees with colorSpace and context; for instance, if
backendRenderTarget has an sRGB configuration, then context must support sRGB,
and colorSpace must be present. Further, backendRenderTarget width and height must
not exceed context capabilities, and the context must be able to support
back-end render targets.

If SK_SUPPORT_GPU is defined as zero, has no effect and returns nullptr.

#Param context  GPU_Context ##
#Param backendRenderTarget  GPU intermediate memory buffer ##
#Param origin   one of: kBottomLeft_GrSurfaceOrigin, kTopLeft_GrSurfaceOrigin ##
#Param colorType  one of: kUnknown_SkColorType, kAlpha_8_SkColorType,
                          kRGB_565_SkColorType, kARGB_4444_SkColorType,
                          kRGBA_8888_SkColorType, kBGRA_8888_SkColorType,
                          kGray_8_SkColorType, kRGBA_F16_SkColorType
##
#Param colorSpace  range of colors ##
#Param surfaceProps  LCD striping orientation and setting for device independent
                     fonts; may be nullptr
##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#Example
#ToDo  remove !fiddle below once backEndTextureRenderTarget is available ##
#Platform !fiddle gpu
    SkPaint paint;
    paint.setTextSize(32);
    GrContext* context = canvas->getGrContext();
    if (!context) {
         canvas->drawString("GPU only!", 20, 40, paint);
         return;
    }
    sk_sp<SkSurface> gpuSurface = SkSurface::MakeFromBackendRenderTarget(context,
            backEndRenderTarget, kTopLeft_GrSurfaceOrigin, kRGBA_8888_SkColorType,
            nullptr, nullptr);
    auto surfaceCanvas = gpuSurface->getCanvas();
    surfaceCanvas->clear(SK_ColorWHITE);
    surfaceCanvas->drawString("GPU rocks!", 20, 40, paint);
    sk_sp<SkImage> image(gpuSurface->makeImageSnapshot());
    canvas->drawImage(image, 0, 0);
##

#SeeAlso MakeFromBackendTexture MakeRenderTarget

#Method ##

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

#Method static sk_sp<SkSurface> MakeFromBackendTextureAsRenderTarget(GrContext* context,
                                                            const GrBackendTexture& backendTexture,
                                                            GrSurfaceOrigin origin,
                                                            int sampleCnt,
                                                            sk_sp<SkColorSpace> colorSpace,
                                                            const SkSurfaceProps* surfaceProps)

Used to wrap a GPU-backed texture as a SkSurface. Skia will treat the texture as
a rendering target only, but unlike NewFromBackendRenderTarget, Skia will manage and own
the associated render target objects (but not the provided texture). Skia will not assume
ownership of the texture and the client must ensure the texture is valid for the lifetime
of the SkSurface.

If SK_SUPPORT_GPU is defined as zero, has no effect and returns nullptr.

#Param context  GPU_Context ##
#Param backendTexture  texture residing on GPU ##
#Param origin   one of: kBottomLeft_GrSurfaceOrigin, kTopLeft_GrSurfaceOrigin ##
#Param sampleCnt  samples per pixel, or 0 to disable full scene anti-aliasing ##
#Param colorSpace  range of colors ##
#Param surfaceProps  LCD striping orientation and setting for device independent
                     fonts; may be nullptr
##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#Example
#Platform !fiddle gpu
    SkPaint paint;
    paint.setTextSize(32);
    GrContext* context = canvas->getGrContext();
    if (!context) {
         canvas->drawString("GPU only!", 20, 40, paint);
         return;
    }
    sk_sp<SkSurface> gpuSurface = SkSurface::MakeFromBackendTextureAsRenderTarget(
            context, backEndTextureRenderTarget, kTopLeft_GrSurfaceOrigin, 0,
            nullptr, nullptr);
    auto surfaceCanvas = gpuSurface->getCanvas();
    surfaceCanvas->clear(SK_ColorWHITE);
    surfaceCanvas->drawString("GPU rocks!", 20, 40, paint);
    sk_sp<SkImage> image(gpuSurface->makeImageSnapshot());
    canvas->drawImage(image, 0, 0);
##

#SeeAlso MakeFromBackendRenderTarget MakeRenderTarget

#Method ##

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

#Method static sk_sp<SkSurface> MakeFromBackendTextureAsRenderTarget(GrContext* context,
                                                            const GrBackendTexture& backendTexture,
                                                            GrSurfaceOrigin origin,
                                                            int sampleCnt,
                                                            SkColorType colorType,
                                                            sk_sp<SkColorSpace> colorSpace,
                                                            const SkSurfaceProps* surfaceProps)

Used to wrap a GPU-backed texture as a SkSurface. Skia will treat the texture as
a rendering target only, but unlike NewFromBackendRenderTarget, Skia will manage and own
the associated render target objects (but not the provided texture). Skia will not assume
ownership of the texture and the client must ensure the texture is valid for the lifetime
of the SkSurface.

If SK_SUPPORT_GPU is defined as zero, has no effect and returns nullptr.

#Param context  GPU_Context ##
#Param backendTexture  texture residing on GPU ##
#Param origin   one of: kBottomLeft_GrSurfaceOrigin, kTopLeft_GrSurfaceOrigin ##
#Param sampleCnt  samples per pixel, or 0 to disable full scene anti-aliasing ##
#Param colorType  one of: kUnknown_SkColorType, kAlpha_8_SkColorType,
                          kRGB_565_SkColorType, kARGB_4444_SkColorType,
                          kRGBA_8888_SkColorType, kBGRA_8888_SkColorType,
                          kGray_8_SkColorType, kRGBA_F16_SkColorType
##
#Param colorSpace  range of colors ##
#Param surfaceProps  LCD striping orientation and setting for device independent
                     fonts; may be nullptr
##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#Example
#Platform !fiddle gpu
    SkPaint paint;
    paint.setTextSize(32);
    GrContext* context = canvas->getGrContext();
    if (!context) {
         canvas->drawString("GPU only!", 20, 40, paint);
         return;
    }
    sk_sp<SkSurface> gpuSurface = SkSurface::MakeFromBackendTextureAsRenderTarget(
            context, backEndTextureRenderTarget, kTopLeft_GrSurfaceOrigin, 0,
            kRGBA_8888_SkColorType, nullptr, nullptr);
    auto surfaceCanvas = gpuSurface->getCanvas();
    surfaceCanvas->clear(SK_ColorWHITE);
    surfaceCanvas->drawString("GPU rocks!", 20, 40, paint);
    sk_sp<SkImage> image(gpuSurface->makeImageSnapshot());
    canvas->drawImage(image, 0, 0);
##

#SeeAlso MakeFromBackendRenderTarget MakeRenderTarget

#Method ##

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

#Method static sk_sp<SkSurface> MakeRenderTarget(GrContext* context, SkBudgeted budgeted,
                                             const SkImageInfo& imageInfo,
                                             int sampleCount, GrSurfaceOrigin surfaceOrigin,
                                             const SkSurfaceProps* surfaceProps,
                                             bool shouldCreateWithMips = false)

Returns offscreen Surface on GPU indicated by context. Allocates memory for
pixels, based on the width, height, and Image_Color_Type in ImageInfo.  budgeted
selects whether allocation for offscreen pixels is tracked by context. imageInfo
describes the pixel format in Image_Color_Type, and transparency in
Image_Alpha_Type, and color matching in Color_Space.

sampleCount requests the number of samples per pixel. 
Pass zero to disable Multi_Sample_Anti_Aliasing.  The request is rounded
up to the next supported count, or rounded down if it is larger than the
maximum supported count.

surfaceOrigin pins either the top-left or the bottom-left corner to the origin.

shouldCreateWithMips hints that Image returned by makeImageSnapshot is Mip_Map.

If SK_SUPPORT_GPU is defined as zero, has no effect and returns nullptr.

#Param context  GPU_Context ##
#Param budgeted  one of: SkBudgeted::kNo, SkBudgeted::kYes ##
#Param imageInfo  width, height, Image_Color_Type, Image_Alpha_Type, Color_Space;
                  width, or height, or both, may be zero
##
#Param sampleCount  samples per pixel, or 0 to disable full scene anti-aliasing ##
#Param surfaceOrigin  one of: kBottomLeft_GrSurfaceOrigin, kTopLeft_GrSurfaceOrigin ##
#Param surfaceProps  LCD striping orientation and setting for device independent
                     fonts; may be nullptr
##
#Param shouldCreateWithMips  hint that Surface will host Mip_Map images ##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#ToDo not sure that this example is relevant; surfaceOrigin doesn't appear to do anything ##
#Example
#Platform gpu
#Height 64
    SkPaint paint;
    paint.setTextSize(32);
    GrContext* context = canvas->getGrContext();
    if (!context) {
         canvas->drawString("GPU only!", 20, 40, paint);
         return;
    }
    SkImageInfo info = SkImageInfo::MakeN32(256, 64, kOpaque_SkAlphaType);
    for (auto surfaceOrigin : { kTopLeft_GrSurfaceOrigin, kBottomLeft_GrSurfaceOrigin } ) {
        auto gpuSurface(SkSurface::MakeRenderTarget(context, SkBudgeted::kNo, info, 0,
               surfaceOrigin, nullptr));
        auto surfaceCanvas = gpuSurface->getCanvas();
        surfaceCanvas->clear(SK_ColorWHITE);
        surfaceCanvas->drawString("GPU rocks!", 20, 40, paint);
        sk_sp<SkImage> image(gpuSurface->makeImageSnapshot());
        canvas->drawImage(image, 0, 0);
       canvas->translate(0, 128);
    }
##

#SeeAlso MakeFromBackendRenderTarget MakeFromBackendTextureAsRenderTarget

#Method ##

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

#Method static sk_sp<SkSurface> MakeRenderTarget(GrContext* context, SkBudgeted budgeted,
                                             const SkImageInfo& imageInfo, int sampleCount,
                                             const SkSurfaceProps* props)

Returns offscreen Surface on GPU indicated by context. Allocates memory for
pixels, based on the width, height, and Image_Color_Type in ImageInfo.  budgeted
selects whether allocation for offscreen pixels is tracked by context. imageInfo
describes the pixel format in Image_Color_Type, and transparency in
Image_Alpha_Type, and color matching in Color_Space.

sampleCount requests the number of samples per pixel. 
Pass zero to disable Multi_Sample_Anti_Aliasing.  The request is rounded
up to the next supported count, or rounded down if it is larger than the
maximum supported count.

Surface bottom-left corner is pinned to the origin.

#Param context  GPU_Context ##
#Param budgeted  one of: SkBudgeted::kNo, SkBudgeted::kYes ##
#Param imageInfo  width, height, Image_Color_Type, Image_Alpha_Type, Color_Space,
                  of Raster_Surface; width, or height, or both, may be zero
##
#Param sampleCount  samples per pixel, or 0 to disable Multi_Sample_Anti_Aliasing ##
#Param props  LCD striping orientation and setting for device independent
              fonts; may be nullptr
##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#Example
#Platform cpu gpu
#Description
LCD text takes advantage of raster striping to improve resolution. Only one of
the four combinations is correct, depending on whether the monitor's LCD is
horizontal or vertical, and whether the order of the stripes is red blue green
or red green blue.
##
void draw(SkCanvas* canvas) {
    auto test_draw = [](SkCanvas* surfaceCanvas) -> void {
        SkPaint paint;
        paint.setAntiAlias(true);
        paint.setLCDRenderText(true);
        paint.setColor(0xFFBBBBBB);
        surfaceCanvas->drawRect(SkRect::MakeWH(128, 64), paint);
        paint.setColor(SK_ColorWHITE);
        paint.setTextSize(32);
        surfaceCanvas->drawString("Pest", 0, 25, paint);
    };
    GrContext* context = canvas->getGrContext();
    SkImageInfo info = SkImageInfo::MakeN32(128, 64, kOpaque_SkAlphaType);
    int y = 0;
    for (auto geometry : { kRGB_H_SkPixelGeometry, kBGR_H_SkPixelGeometry,
                           kRGB_V_SkPixelGeometry, kBGR_V_SkPixelGeometry } ) {
        SkSurfaceProps props(0, geometry);
        sk_sp<SkSurface> surface = context ? SkSurface::MakeRenderTarget(
                context, SkBudgeted::kNo, info, 0, &props) : SkSurface::MakeRaster(info, &props);
        test_draw(surface->getCanvas());
        surface->draw(canvas, 0, y, nullptr);
        sk_sp<SkImage> image(surface->makeImageSnapshot());
        SkAutoCanvasRestore acr(canvas, true);
        canvas->scale(8, 8);
        canvas->drawImage(image, 12, y / 8);
        y += 64;
    }
}
##

#SeeAlso MakeFromBackendRenderTarget MakeFromBackendTextureAsRenderTarget

#Method ##

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

#Method static sk_sp<SkSurface> MakeRenderTarget(GrContext* context, SkBudgeted budgeted,
                                             const SkImageInfo& imageInfo)

Returns offscreen Surface on GPU indicated by context. Allocates memory for
pixels, based on the width, height, and Image_Color_Type in ImageInfo.  budgeted
selects whether allocation for offscreen pixels is tracked by context. imageInfo
describes the pixel format in Image_Color_Type, and transparency in
Image_Alpha_Type, and color matching in Color_Space.

Surface bottom-left corner is pinned to the origin.

#Param context  GPU_Context ##
#Param budgeted  one of: SkBudgeted::kNo, SkBudgeted::kYes ##
#Param imageInfo  width, height, Image_Color_Type, Image_Alpha_Type, Color_Space,
                  of Raster_Surface; width, or height, or both, may be zero
##

#Return Surface if all parameters are valid; otherwise, nullptr ##

#Example
#Platform gpu
    SkPaint paint;
    paint.setTextSize(32);
    GrContext* context = canvas->getGrContext();
    if (!context) {
         canvas->drawString("GPU only!", 20, 40, paint);
         return;
    }
    SkImageInfo info = SkImageInfo::MakeN32(256, 64, kOpaque_SkAlphaType);
    auto gpuSurface(SkSurface::MakeRenderTarget(context, SkBudgeted::kNo, info));
    auto surfaceCanvas = gpuSurface->getCanvas();
    surfaceCanvas->clear(SK_ColorWHITE);
    surfaceCanvas->drawString("GPU rocks!", 20, 40, paint);
    sk_sp<SkImage> image(gpuSurface->makeImageSnapshot());
    canvas->drawImage(image, 0, 0);
##

#SeeAlso MakeFromBackendRenderTarget MakeFromBackendTextureAsRenderTarget

#Method ##

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

#Method static sk_sp<SkSurface> MakeNull(int width, int height)

Returns Surface without backing pixels. Drawing to Canvas returned from Surface
has no effect. Calling makeImageSnapshot() on returned Surface returns nullptr.

#Param width  one or greater ##
#Param height  one or greater ##

#Return Surface if width and height are positive; otherwise, nullptr ##

#Example
    SkDebugf("SkSurface::MakeNull(0, 0) %c= nullptr\n", SkSurface::MakeNull(0, 0) == nullptr ?
             '=' : '!');
    const int w = 37;
    const int h = 1000;
    auto surf = SkSurface::MakeNull(w, h);
    auto nullCanvas = surf->getCanvas();
    nullCanvas->drawPaint(SkPaint());   // does not crash, nothing draws
    SkDebugf("surf->makeImageSnapshot() %c= nullptr\n", surf->makeImageSnapshot() == nullptr ?
            '=' : '!');
#StdOut
SkSurface::MakeNull(0, 0) == nullptr
surf->makeImageSnapshot() == nullptr
##
##

#SeeAlso MakeRaster MakeRenderTarget

#Method ##

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

#Method int width() const

Returns pixel count in each row; may be zero or greater.

#Return number of pixel columns ##

#Example
    const int width = 37;
    const int height = 1000;
    auto surf = SkSurface::MakeNull(width, height);
    auto nullCanvas = surf->getCanvas();
    SkDebugf("surface width=%d  canvas width=%d\n", surf->width(),
             nullCanvas->getBaseLayerSize().fWidth);
#StdOut
surface width=37  canvas width=37
##
##

#SeeAlso height()

#Method ##

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

#Method int height() const

Returns pixel row count; may be zero or greater.

#Return number of pixel rows ##

#Example
    const int width = 37;
    const int height = 1000;
    auto surf = SkSurface::MakeNull(width, height);
    auto nullCanvas = surf->getCanvas();
    SkDebugf("surface height=%d  canvas height=%d\n", surf->height(),
             nullCanvas->getBaseLayerSize().fHeight);
#StdOut
surface height=1000  canvas height=1000
##
##

#SeeAlso width()

#Method ##

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

#Method uint32_t generationID()

Returns unique value identifying the content of Surface. Returned value changes
each time the content changes. Content is changed by drawing, or by calling
notifyContentWillChange.

#Return unique content identifier ##

#Example
    auto surface = SkSurface::MakeRasterN32Premul(1, 1);
    for (int i = 0; i < 3; ++i) {
        SkDebugf("surface generationID: %d\n", surface->generationID());
        if (0 == i) {
            surface->getCanvas()->drawColor(SK_ColorBLACK);
        } else {
            surface->notifyContentWillChange(SkSurface::kDiscard_ContentChangeMode);
        }
    }
#StdOut
surface generationID: 1
surface generationID: 2
surface generationID: 3
##
##

#SeeAlso notifyContentWillChange ContentChangeMode getCanvas

#Method ##

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

#Enum ContentChangeMode

#Code
    enum ContentChangeMode {
        kDiscard_ContentChangeMode,
        kRetain_ContentChangeMode,
    };
##

ContentChangeMode members are parameters to notifyContentWillChange.

#Const kDiscard_ContentChangeMode
Pass to notifyContentWillChange to discard surface contents when
the surface is cleared or overwritten.
##
#Const kRetain_ContentChangeMode
Pass to notifyContentWillChange when to preserve surface contents.
If a snapshot has been generated, this copies the Surface contents.
##

#SeeAlso notifyContentWillChange generationID

#Enum ##

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

#Method void notifyContentWillChange(ContentChangeMode mode)

Notifies that Surface contents will be changed by code outside of Skia.
Subsequent calls to generationID return a different value.

mode is normally passed as kRetain_ContentChangeMode.

#Private
CAN WE DEPRECATE THIS?
##

#Param mode  one of: kDiscard_ContentChangeMode, kRetain_ContentChangeMode ##

#Example
    auto surface = SkSurface::MakeRasterN32Premul(1, 1);
    for (int i = 0; i < 3; ++i) {
        SkDebugf("surface generationID: %d\n", surface->generationID());
        if (0 == i) {
            surface->getCanvas()->drawColor(SK_ColorBLACK);
        } else {
            surface->notifyContentWillChange(SkSurface::kDiscard_ContentChangeMode);
        }
    }
##

#SeeAlso ContentChangeMode generationID

#Method ##

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

#Enum BackendHandleAccess

#Code
    enum BackendHandleAccess {
        kFlushRead_BackendHandleAccess,
        kFlushWrite_BackendHandleAccess,
        kDiscardWrite_BackendHandleAccess,
    };

    static const BackendHandleAccess kFlushRead_TextureHandleAccess =
            kFlushRead_BackendHandleAccess;
    static const BackendHandleAccess kFlushWrite_TextureHandleAccess =
            kFlushWrite_BackendHandleAccess;
    static const BackendHandleAccess kDiscardWrite_TextureHandleAccess =
            kDiscardWrite_BackendHandleAccess;
##

#Const kFlushRead_BackendHandleAccess 0
Caller may read from the back-end object.
##
#Const kFlushWrite_BackendHandleAccess 1
Caller may write to the back-end object.
##
#Const kDiscardWrite_BackendHandleAccess 2
Caller must overwrite the entire back-end object.
##

#Const kFlushRead_TextureHandleAccess 0
Deprecated.
#Deprecated 
##
##
#Const kFlushWrite_TextureHandleAccess 1
Deprecated.
#Deprecated 
##
##
#Const kDiscardWrite_TextureHandleAccess 2
Deprecated.
#Deprecated 
##
##

#Example
#Platform gpu
    SkPaint paint;
    paint.setTextSize(32);
    GrContext* context = canvas->getGrContext();
    if (!context) {
         canvas->drawString("GPU only!", 20, 40, paint);
         return;
    }
    sk_sp<SkSurface> gpuSurface = SkSurface::MakeRenderTarget(
            context, SkBudgeted::kYes, SkImageInfo::MakeN32Premul(10, 10));
    int y = 20;
    SkString str;
    paint.setTextSize(16);
    for (auto access : { SkSurface::kFlushRead_BackendHandleAccess, 
                         SkSurface::kFlushWrite_BackendHandleAccess,
                         SkSurface::kDiscardWrite_BackendHandleAccess } ) {
        sk_sp<SkImage> image(gpuSurface->makeImageSnapshot());
        str.printf("uniqueID=%d", image->uniqueID());
        canvas->drawString(str, 20, y += 20, paint);
        GrBackendObject backendObject = gpuSurface->getTextureHandle(access);
        str.printf("backendObject %c= 0", backendObject != 0 ? '!' : '=');
        canvas->drawString(str, 20, y += 20, paint);
    }
    sk_sp<SkImage> image(gpuSurface->makeImageSnapshot());
    str.printf("final image uniqueID=%d", image->uniqueID());
    canvas->drawString(str, 20, y += 20, paint);
##

#SeeAlso getTextureHandle getRenderTargetHandle

#Enum ##

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

#Method GrBackendObject getTextureHandle(BackendHandleAccess backendHandleAccess)

Returns the GPU back-end reference of the texture used by Surface, or zero
if Surface is not backed by a GPU texture.

The returned texture handle is only valid until the next draw into Surface,
or when Surface is deleted.

#Param backendHandleAccess  one of:  kFlushRead_BackendHandleAccess,
        kFlushWrite_BackendHandleAccess, kDiscardWrite_BackendHandleAccess
##

#Return GPU texture reference ##

#Example
#Platform gpu
#Height 64
    SkPaint paint;
    paint.setTextSize(32);
    GrContext* context = canvas->getGrContext();
    if (!context) {
         canvas->drawString("GPU only!", 20, 40, paint);
         return;
    }
    sk_sp<SkSurface> gpuSurface = SkSurface::MakeRenderTarget(
            context, SkBudgeted::kYes, SkImageInfo::MakeN32Premul(10, 10));
    GrBackendObject backendObject = gpuSurface->getTextureHandle(
            SkSurface::kFlushRead_BackendHandleAccess);
    if (backendObject) {
        SkString str;
        str.printf("backendObject=%08x", backendObject);
        paint.setTextSize(16);
        canvas->drawString(str, 20, 40, paint);
    }
##

#SeeAlso getRenderTargetHandle GrBackendObject BackendHandleAccess

#Method ##

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

#Method bool getRenderTargetHandle(GrBackendObject* backendObject,
                               BackendHandleAccess backendHandleAccess)

Returns true and stores the GPU back-end reference of the render target used
by Surface in backendObject.

Return false if Surface is not backed by a GPU render target, and leaves
backendObject unchanged.

The returned render target handle is only valid until the next draw into Surface,
or when Surface is deleted.

In OpenGL this returns the frame buffer object ID.

#Param backendObject  GPU intermediate memory buffer ##
#Param backendHandleAccess  one of:  kFlushRead_BackendHandleAccess,
        kFlushWrite_BackendHandleAccess, kDiscardWrite_BackendHandleAccess
##

#Return true if Surface is backed by GPU texture ##

#Example
#Platform gpu
#Height 64
    SkPaint paint;
    paint.setTextSize(32);
    GrContext* context = canvas->getGrContext();
    if (!context) {
         canvas->drawString("GPU only!", 20, 40, paint);
         return;
    }
    sk_sp<SkSurface> gpuSurface = SkSurface::MakeRenderTarget(
            context, SkBudgeted::kYes, SkImageInfo::MakeN32Premul(10, 10));
    GrBackendObject backendObject;
    if (gpuSurface->getRenderTargetHandle(&backendObject, 
            SkSurface::kFlushRead_BackendHandleAccess)) {
        SkString str;
        str.printf("backendObject=%d", backendObject);
        paint.setTextSize(16);
        canvas->drawString(str, 20, 40, paint);
    }
##

#SeeAlso getTextureHandle GrBackendObject BackendHandleAccess

#Method ##

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

#Method SkCanvas* getCanvas()

Returns Canvas that draws into Surface. Subsequent calls return the same Canvas.
Canvas returned is managed and owned by Surface, and is deleted when Surface
is deleted.

#Return drawing Canvas for Surface ##

#Example
#Height 64
    sk_sp<SkSurface> surface(SkSurface::MakeRasterN32Premul(64, 64));
    SkCanvas* surfaceCanvas = surface->getCanvas();
    surfaceCanvas->clear(SK_ColorBLUE);
    SkPaint paint;
    paint.setTextSize(40);
    surfaceCanvas->drawString("\xF0\x9F\x98\x81", 12, 45, paint);
    surface->draw(canvas, 0, 0, nullptr);
##

#SeeAlso makeSurface makeImageSnapshot draw()

#Method ##

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

#Method sk_sp<SkSurface> makeSurface(const SkImageInfo& imageInfo)

Returns a compatible Surface, or nullptr. Returned Surface contains
the same raster, GPU, or null properties as the original. Returned Surface
does not share the same pixels.

Returns nullptr if imageInfo width or height are zero, or if imageInfo
is incompatible with Surface.
 
#Param imageInfo  width, height, Image_Color_Type, Image_Alpha_Type, Color_Space,
                  of Surface; width and height must be greater than zero
##

#Return compatible Surface or nullptr ##

#Example
#Height 96
    sk_sp<SkSurface> big(SkSurface::MakeRasterN32Premul(64, 64));
    sk_sp<SkSurface> lil(big->makeSurface(SkImageInfo::MakeN32(32, 32, kPremul_SkAlphaType)));
    big->getCanvas()->clear(SK_ColorRED);
    lil->getCanvas()->clear(SK_ColorBLACK);
    SkPixmap pixmap;
    if (big->peekPixels(&pixmap)) {
        SkBitmap bigBits;
        bigBits.installPixels(pixmap);
        canvas->drawBitmap(bigBits, 0, 0);
    }
    if (lil->peekPixels(&pixmap)) {
        SkBitmap lilBits;
        lilBits.installPixels(pixmap);
        canvas->drawBitmap(lilBits, 64, 64);
    }
##

#SeeAlso makeImageSnapshot getCanvas draw()

#Method ##

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

#Method sk_sp<SkImage> makeImageSnapshot()

Returns Image capturing Surface contents. Subsequent drawing to Surface contents
are not captured. Image allocation is accounted for if Surface was created with
SkBudgeted::kYes.

#Return Image initialized with Surface contents ##

#Example
#Height 64
    sk_sp<SkSurface> big(SkSurface::MakeRasterN32Premul(64, 64));
    sk_sp<SkSurface> lil(big->makeSurface(SkImageInfo::MakeN32(32, 32, kPremul_SkAlphaType)));
    big->getCanvas()->clear(SK_ColorRED);
    lil->getCanvas()->clear(SK_ColorBLACK);
    sk_sp<SkImage> early(big->makeImageSnapshot());
    lil->draw(big->getCanvas(), 16, 16, nullptr);
    sk_sp<SkImage> later(big->makeImageSnapshot());
    canvas->drawImage(early, 0, 0);
    canvas->drawImage(later, 128, 0);
##

#SeeAlso draw getCanvas

#Method ##

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

#Method void draw(SkCanvas* canvas, SkScalar x, SkScalar y, const SkPaint* paint)

Draws Surface contents to canvas, with its top-left corner at (x, y).

If Paint paint is not nullptr, apply Color_Filter, Color_Alpha, Image_Filter,
Blend_Mode, and Draw_Looper.

#Param canvas  Canvas drawn into ##
#Param x  horizontal offset in Canvas ##
#Param y  vertical offset in Canvas ##
#Param paint  Paint containing Blend_Mode, Color_Filter, Image_Filter,
              and so on; or nullptr 
##

#Example
#Height 64
    sk_sp<SkSurface> big(SkSurface::MakeRasterN32Premul(64, 64));
    sk_sp<SkSurface> lil(big->makeSurface(SkImageInfo::MakeN32(32, 32, kPremul_SkAlphaType)));
    big->getCanvas()->clear(SK_ColorRED);
    lil->getCanvas()->clear(SK_ColorBLACK);
    lil->draw(big->getCanvas(), 16, 16, nullptr);
    SkPixmap pixmap;
    if (big->peekPixels(&pixmap)) {
        SkBitmap bigBits;
        bigBits.installPixels(pixmap);
        canvas->drawBitmap(bigBits, 0, 0);
    }
##

#SeeAlso makeImageSnapshot getCanvas

#Method ##

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

#Method bool peekPixels(SkPixmap* pixmap)

Copies Surface pixel address, row bytes, and Image_Info to Pixmap, if address
is available, and returns true. If pixel address is not available, return
false and leave Pixmap unchanged.

pixmap contents become invalid on any future change to Surface.

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

#Return true if Surface has direct access to pixels ##

#Example
#Height 64
    sk_sp<SkSurface> surf(SkSurface::MakeRasterN32Premul(64, 64));
    auto surfCanvas = surf->getCanvas();
    surfCanvas->clear(SK_ColorRED);
    SkPaint paint;
    paint.setTextSize(40);
    surfCanvas->drawString("&", 16, 48, paint);
    SkPixmap pixmap;
    if (surf->peekPixels(&pixmap)) {
        SkBitmap surfBits;
        surfBits.installPixels(pixmap);
        canvas->drawBitmap(surfBits, 0, 0);
    }
##

#SeeAlso readPixels

#Method ##

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

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

Copies Rect of pixels to dst.

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

Pixels are readable when Surface is raster, or backed by a GPU.

The destination pixel storage must be allocated by the caller.

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

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

Does not copy, and returns false if:

#List
# Source and destination rectangles do not intersect. ##
# Pixmap pixels could not be allocated. ##
# dst.rowBytes() is too small to contain one row of pixels. ##
##

#Param dst  storage for pixels copied from Surface ##
#Param srcX  offset into readable pixels in x; may be negative ##
#Param srcY  offset into readable pixels in y; may be negative ##

#Return true if pixels were copied ##

#Example
#Height 32
    sk_sp<SkSurface> surf(SkSurface::MakeRasterN32Premul(64, 64));
    auto surfCanvas = surf->getCanvas();
    surfCanvas->clear(SK_ColorRED);
    SkPaint paint;
    paint.setTextSize(40);
    surfCanvas->drawString("&", 0, 32, paint);
    std::vector<SkPMColor> storage;
    storage.resize(surf->width() * surf->height());
    SkPixmap pixmap(SkImageInfo::MakeN32Premul(32, 32), &storage.front(),
                    surf->width() * sizeof(storage[0]));
    if (surf->readPixels(pixmap, 0, 0)) {
        SkBitmap surfBits;
        surfBits.installPixels(pixmap);
        canvas->drawBitmap(surfBits, 0, 0);
    }
##

#SeeAlso peekPixels

#Method ##

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

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

Copies Rect of pixels from Canvas into dstPixels.

Source Rect corners are (srcX, srcY) and Surface (width(), 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 Surface is raster, or backed by a GPU.

The destination pixel storage must be allocated by the caller.

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

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

Does not copy, and returns false if:

#List
# Source and destination rectangles do not intersect. ##
# Surface pixels could not be converted to dstInfo.colorType() or dstInfo.alphaType(). ##
# dstRowBytes is too small to contain one row of pixels. ##
##

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

#Return true if pixels were copied ##

#Example
#Height 64
#Description
    A black oval drawn on a red background provides an image to copy.
    readPixels copies one quarter of the Surface into each of the four corners.
    The copied quarter ovals overdraw the original oval.
##
    sk_sp<SkSurface> surf(SkSurface::MakeRasterN32Premul(64, 64));
    auto surfCanvas = surf->getCanvas();
    surfCanvas->clear(SK_ColorRED);
    SkPaint paint;
    surfCanvas->drawOval({4, 8, 58, 54}, paint);
    SkImageInfo info = SkImageInfo::Make(64, 64, kBGRA_8888_SkColorType, kPremul_SkAlphaType);
    sk_sp<SkData> data(SkData::MakeUninitialized(info.minRowBytes() * info.height()));
    sk_bzero(data->writable_data(), info.minRowBytes() * info.height());
    for (int x : { 32, -32 } ) {
        for (int y : { 32, -32 } ) {
            surf->readPixels(info, data->writable_data(), info.minRowBytes(), x, y);
        } 
    }
    sk_sp<SkImage> image = SkImage::MakeRasterData(info, data, info.minRowBytes());
    canvas->drawImage(image, 0, 0);
##

#SeeAlso peekPixels

#Method ##

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

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

Copies Rect of pixels from Surface into bitmap.

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

Pixels are readable when Surface is raster, or backed by a GPU.

The destination pixel storage must be allocated by the caller.

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

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

Does not copy, and returns false if:

#List
# Source and destination rectangles do not intersect. ##
# Surface pixels could not be converted to dst.colorType() or dst.alphaType(). ##
# dst pixels could not be allocated. ##
# dst.rowBytes() is too small to contain one row of pixels. ##
##

#Param dst  storage for pixels copied from Surface ##
#Param srcX  offset into readable pixels in x; may be negative ##
#Param srcY  offset into readable pixels in y; may be negative ##

#Return true if pixels were copied ##

#Example
    sk_sp<SkSurface> surf(SkSurface::MakeRasterN32Premul(64, 64));
    auto surfCanvas = surf->getCanvas();
    surfCanvas->clear(SK_ColorGREEN);
    SkPaint paint;
    surfCanvas->drawOval({2, 10, 58, 54}, paint);
    SkImageInfo info = SkImageInfo::Make(64, 64, kBGRA_8888_SkColorType, kPremul_SkAlphaType);
    SkBitmap bitmap;
    bitmap.setInfo(info);
    bitmap.allocPixels();
    for (int x : { 32, -32 } ) {
        for (int y : { 32, -32 } ) {
            surf->readPixels(bitmap, x, y);
        } 
    }
    canvas->drawBitmap(bitmap, 0, 0);
##

#SeeAlso peekPixels

#Method ##

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

#Method const SkSurfaceProps& props() const

Returns Surface_Properties for surface.

#Return LCD striping orientation and setting for device independent fonts ##

#Example
    const char* names[] = { "Unknown", "RGB_H", "BGR_H", "RGB_V", "BGR_V" };
    sk_sp<SkSurface> surf(SkSurface::MakeRasterN32Premul(64, 64));
    SkDebugf("surf.props(): k%s_SkPixelGeometry\n", names[surf->props().pixelGeometry()]);
#StdOut
surf.props(): kRGB_H_SkPixelGeometry
##
##

#SeeAlso SkSurfaceProps

#Method ##

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

#Method void prepareForExternalIO()

To be deprecated.

#NoExample
##

#Method ##

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

#Method void flush()

Issues pending Surface commands to the GPU-backed API and resolves any Surface MSAA.

Skia flushes as needed, so it is not necessary to call this if Skia manages
drawing and object lifetime. Call when interleaving Skia calls with native
GPU calls.

#NoExample
##

#SeeAlso GrBackendSemaphore

#Method ##

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

#Method GrSemaphoresSubmitted flushAndSignalSemaphores(int numSemaphores,
                                                   GrBackendSemaphore signalSemaphores[])

Issues pending Surface commands to the GPU-backed API and resolves any Surface MSAA.
After issuing all commands, signalSemaphores of count numSemaphores semaphores
are signaled by the GPU.

For each GrBackendSemaphore in signalSemaphores:
if GrBackendSemaphore is initialized, the GPU back-end uses the semaphore as is;
otherwise, a new semaphore is created and initializes GrBackendSemaphore.

The caller must delete the semaphores created and returned in signalSemaphores.
GrBackendSemaphore can be deleted as soon as this function returns.

If the back-end API is OpenGL only uninitialized GrBackendSemaphores are supported.

If the back-end API is Vulkan semaphores may be initialized or uninitialized.
If uninitialized, created semaphores are valid only with the VkDevice
with which they were created.

If GrSemaphoresSubmitted::kNo is returned, the GPU back-end did not create or
add any semaphores to signal on the GPU; the caller should not instruct the GPU
to wait on any of the semaphores. 

Pending surface commands are flushed regardless of the return result.

#Param numSemaphores  size of signalSemaphores array ##
#Param signalSemaphores  array of semaphore containers ##

#Return one of: GrSemaphoresSubmitted::kYes, GrSemaphoresSubmitted::kNo ##

#NoExample
##

#SeeAlso wait GrBackendSemaphore

#Method ##

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

#Method bool wait(int numSemaphores, const GrBackendSemaphore* waitSemaphores)

Inserts a list of GPU semaphores that the current GPU-backed API must wait on before
executing any more commands on the GPU for this surface. Skia will take ownership of the
underlying semaphores and delete them once they have been signaled and waited on.
If this call returns false, then the GPU back-end will not wait on any passed in semaphores,
and the client will still own the semaphores.

#Param numSemaphores  size of waitSemaphores array ##
#Param waitSemaphores  array of semaphore containers ##

#Return true if GPU is waiting on semaphores ##

#Example
#ToDo this is copy and paste silliness masquerading as an example. Probably need gpu
      globals and definitely need gpu expertise to make a real example out of this
 ##
#Platform !fiddle gpu
#Height 64
    SkPaint paint;
    paint.setTextSize(32);
    GrContext* context = canvas->getGrContext();
    if (!context) {
         canvas->drawString("GPU only!", 20, 40, paint);
         return;
    }
    GrBackendSemaphore semaphore;
    sk_sp<SkSurface> surface = SkSurface::MakeRenderTarget(
            context, SkBudgeted::kYes, SkImageInfo::MakeN32Premul(64, 64));
    surface->flushAndSignalSemaphores(1, &semaphore);
    sk_sp<SkImage> image = surface->makeImageSnapshot();
    GrBackendObject backendImage = image->getTextureHandle(false); // unused
    SkASSERT(backendImage);
    const SkImageInfo childImageInfo = SkImageInfo::Make(64, 64,
              kRGBA_8888_SkColorType, kPremul_SkAlphaType);
    sk_sp<SkSurface> childSurface(SkSurface::MakeRenderTarget(context, SkBudgeted::kNo,
              childImageInfo, 0, kTopLeft_GrSurfaceOrigin, nullptr));
    GrBackendTexture backendTexture;
    sk_sp<SkImage> childImage = SkImage::MakeFromTexture(context,
              backendTexture,   // undefined
              kTopLeft_GrSurfaceOrigin, kPremul_SkAlphaType, nullptr);
    SkCanvas* childCanvas = childSurface->getCanvas();
    childCanvas->clear(SK_ColorRED);
    childSurface->wait(1, &semaphore);
    childCanvas->drawImage(childImage, 32, 0);
    childSurface->draw(canvas, 0, 0, nullptr);
##

#SeeAlso flushAndSignalSemaphores GrBackendSemaphore

#Method ##

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

#Method bool characterize(SkSurfaceCharacterization* characterization) const

Initializes Surface_Characterization that can be used to perform GPU back-end
pre-processing in a separate thread. Typically this is used to divide drawing
into multiple tiles. DeferredDisplayListRecorder records the drawing commands
for each tile.

Return true if Surface supports characterization. Raster_Surface returns false.

#Param characterization  properties for parallel drawing ##

#Return true if supported ##

#Example
#Platform gpu
#Height 64
    SkPaint paint;
    paint.setTextSize(32);
    GrContext* context = canvas->getGrContext();
    if (!context) {
         canvas->drawString("GPU only!", 20, 40, paint);
         return;
    }
    sk_sp<SkSurface> gpuSurface = SkSurface::MakeRenderTarget(
            context, SkBudgeted::kYes, SkImageInfo::MakeN32Premul(64, 64));
    SkSurfaceCharacterization characterization;
    if (!gpuSurface->characterize(&characterization)) {
         canvas->drawString("characterization unsupported", 20, 40, paint);
         return;
    }
    // start of threadable work 
    SkDeferredDisplayListRecorder recorder(characterization);
    SkCanvas* subCanvas = recorder.getCanvas();
    subCanvas->clear(SK_ColorGREEN);
    std::unique_ptr<SkDeferredDisplayList> displayList = recorder.detach();
    // end of threadable work
    gpuSurface->draw(displayList.get());
    sk_sp<SkImage> img = gpuSurface->makeImageSnapshot();
    canvas->drawImage(std::move(img), 0, 0);
##

#SeeAlso draw() SkSurfaceCharacterization SkDeferredDisplayList

#Method ##

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

#Method bool draw(SkDeferredDisplayList* deferredDisplayList)

Draws deferred display list created using SkDeferredDisplayListRecorder.
Has no effect and returns false if Surface_Characterization stored in
deferredDisplayList is not compatible with Surface.

Raster_Surface returns false.

#Param deferredDisplayList  drawing commands ##

#Return false if deferredDisplayList is not compatible ##

#Example
#Height 64
#Platform gpu cpu
    SkPaint paint;
    paint.setTextSize(16);
    sk_sp<SkSurface> gpuSurface = SkSurface::MakeRasterN32Premul(64, 64);
    SkSurfaceCharacterization characterization;
    if (!gpuSurface->characterize(&characterization)) {
         canvas->drawString("characterization unsupported", 20, 40, paint);
         return;
    }
    // start of threadable work 
    SkDeferredDisplayListRecorder recorder(characterization);
    SkCanvas* subCanvas = recorder.getCanvas();
    subCanvas->clear(SK_ColorGREEN);
    std::unique_ptr<SkDeferredDisplayList> displayList = recorder.detach();
    // end of threadable work
    gpuSurface->draw(displayList.get());
    sk_sp<SkImage> img = gpuSurface->makeImageSnapshot();
    canvas->drawImage(std::move(img), 0, 0);
##

#SeeAlso characterize() SkSurfaceCharacterization SkDeferredDisplayList

#Method ##

#Class SkSurface ##

#Topic Surface ##