src/gpu/GrGpu.h

/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrGpu_DEFINED
#define GrGpu_DEFINED

#include "include/core/SkPath.h"
#include "include/core/SkSurface.h"
#include "include/gpu/GrTypes.h"
#include "include/private/SkTArray.h"
#include "src/gpu/GrAllocator.h"
#include "src/gpu/GrCaps.h"
#include "src/gpu/GrGpuCommandBuffer.h"
#include "src/gpu/GrProgramDesc.h"
#include "src/gpu/GrSamplePatternDictionary.h"
#include "src/gpu/GrSwizzle.h"
#include "src/gpu/GrTextureProducer.h"
#include "src/gpu/GrXferProcessor.h"
#include <map>

class GrBackendRenderTarget;
class GrBackendSemaphore;
class GrGpuBuffer;
class GrContext;
struct GrContextOptions;
class GrGLContext;
class GrMesh;
class GrPath;
class GrPathRenderer;
class GrPathRendererChain;
class GrPathRendering;
class GrPipeline;
class GrPrimitiveProcessor;
class GrRenderTarget;
class GrSemaphore;
class GrStencilAttachment;
class GrStencilSettings;
class GrSurface;
class GrTexture;
class SkJSONWriter;

class GrGpu : public SkRefCnt {
public:
    GrGpu(GrContext* context);
    ~GrGpu() override;

    GrContext* getContext() { return fContext; }
    const GrContext* getContext() const { return fContext; }

    /**
     * Gets the capabilities of the draw target.
     */
    const GrCaps* caps() const { return fCaps.get(); }
    sk_sp<const GrCaps> refCaps() const { return fCaps; }

    GrPathRendering* pathRendering() { return fPathRendering.get();  }

    enum class DisconnectType {
        // No cleanup should be attempted, immediately cease making backend API calls
        kAbandon,
        // Free allocated resources (not known by GrResourceCache) before returning and
        // ensure no backend backend 3D API calls will be made after disconnect() returns.
        kCleanup,
    };

    // Called by GrContext when the underlying backend context is already or will be destroyed
    // before GrContext.
    virtual void disconnect(DisconnectType);

    /**
     * The GrGpu object normally assumes that no outsider is setting state
     * within the underlying 3D API's context/device/whatever. This call informs
     * the GrGpu that the state was modified and it shouldn't make assumptions
     * about the state.
     */
    void markContextDirty(uint32_t state = kAll_GrBackendState) { fResetBits |= state; }

    /**
     * Creates a texture object. If renderable is kYes then the returned texture can
     * be used as a render target by calling GrTexture::asRenderTarget(). Not all
     * pixel configs can be used as render targets. Support for configs as textures
     * or render targets can be checked using GrCaps.
     *
     * @param desc           describes the texture to be created.
     * @param renderable     should the resulting texture be renderable
     * @param renderTargetSampleCnt The number of samples to use for rendering if renderable is
     *                       kYes. If renderable is kNo then this must be 1.
     * @param budgeted       does this texture count against the resource cache budget?
     * @param isProtected    should the texture be created as protected.
     * @param texels         array of mipmap levels containing texel data to load.
     *                       If level i has pixels then it is assumed that its dimensions are
     *                       max(1, floor(desc.fWidth / 2)) by max(1, floor(desc.fHeight / 2)).
     *                       If texels[i].fPixels == nullptr for all i <= mipLevelCount or
     *                       mipLevelCount is 0 then the texture's contents are uninitialized.
     *                       If a level has non-null pixels, its row bytes must be a multiple of the
     *                       config's bytes-per-pixel. The row bytes must be tight to the
     *                       level width if !caps->writePixelsRowBytesSupport().
     *                       If mipLevelCount > 1 and texels[i].fPixels != nullptr for any i > 0
     *                       then all levels must have non-null pixels. All levels must have
     *                       non-null pixels if GrCaps::createTextureMustSpecifyAllLevels() is true.
     * @param mipLevelCount  the number of levels in 'texels'. May be 0, 1, or
     *                       floor(max((log2(desc.fWidth), log2(desc.fHeight)))). It must be the
     *                       latter if GrCaps::createTextureMustSpecifyAllLevels() is true.
     * @return  The texture object if successful, otherwise nullptr.
     */
    sk_sp<GrTexture> createTexture(const GrSurfaceDesc& desc, GrRenderable renderable,
                                   int renderTargetSampleCnt, SkBudgeted, GrProtected isProtected,
                                   const GrMipLevel texels[], int mipLevelCount);

    /**
     * Simplified createTexture() interface for when there is no initial texel data to upload.
     */
    sk_sp<GrTexture> createTexture(const GrSurfaceDesc&, GrRenderable, int renderTargetSampleCnt,
                                   SkBudgeted, GrProtected);

    sk_sp<GrTexture> createCompressedTexture(int width, int height, SkImage::CompressionType,
                                             SkBudgeted, const void* data, size_t dataSize);

    /**
     * Implements GrResourceProvider::wrapBackendTexture
     */
    sk_sp<GrTexture> wrapBackendTexture(const GrBackendTexture&, GrColorType,
                                        GrWrapOwnership, GrWrapCacheable, GrIOType);

    /**
     * Implements GrResourceProvider::wrapRenderableBackendTexture
     */
    sk_sp<GrTexture> wrapRenderableBackendTexture(const GrBackendTexture&, int sampleCnt,
                                                  GrColorType, GrWrapOwnership, GrWrapCacheable);

    /**
     * Implements GrResourceProvider::wrapBackendRenderTarget
     */
    sk_sp<GrRenderTarget> wrapBackendRenderTarget(const GrBackendRenderTarget&,
                                                  GrColorType colorType);

    /**
     * Implements GrResourceProvider::wrapBackendTextureAsRenderTarget
     */
    sk_sp<GrRenderTarget> wrapBackendTextureAsRenderTarget(const GrBackendTexture&,
                                                           int sampleCnt,
                                                           GrColorType colorType);

    /**
     * Implements GrResourceProvider::wrapVulkanSecondaryCBAsRenderTarget
     */
    sk_sp<GrRenderTarget> wrapVulkanSecondaryCBAsRenderTarget(const SkImageInfo&,
                                                              const GrVkDrawableInfo&);

    /**
     * Creates a buffer in GPU memory. For a client-side buffer use GrBuffer::CreateCPUBacked.
     *
     * @param size            size of buffer to create.
     * @param intendedType    hint to the graphics subsystem about what the buffer will be used for.
     * @param accessPattern   hint to the graphics subsystem about how the data will be accessed.
     * @param data            optional data with which to initialize the buffer.
     *
     * @return the buffer if successful, otherwise nullptr.
     */
    sk_sp<GrGpuBuffer> createBuffer(size_t size, GrGpuBufferType intendedType,
                                    GrAccessPattern accessPattern, const void* data = nullptr);

    /**
     * Resolves MSAA.
     */
    void resolveRenderTarget(GrRenderTarget*);

    /**
     * Uses the base of the texture to recompute the contents of the other levels.
     */
    bool regenerateMipMapLevels(GrTexture*);

    /**
     * If the backend API has stateful texture bindings, this resets them back to defaults.
     */
    void resetTextureBindings();

    /**
     * Reads a rectangle of pixels from a render target. No sRGB/linear conversions are performed.
     *
     * @param surface           The surface to read from
     * @param left              left edge of the rectangle to read (inclusive)
     * @param top               top edge of the rectangle to read (inclusive)
     * @param width             width of rectangle to read in pixels.
     * @param height            height of rectangle to read in pixels.
     * @param surfaceColorType  the color type for this use of the surface.
     * @param dstColorType      the color type of the destination buffer.
     * @param buffer            memory to read the rectangle into.
     * @param rowBytes          the number of bytes between consecutive rows. Must be a multiple of
     *                          dstColorType's bytes-per-pixel. Must be tight to width if
     *                          !caps->readPixelsRowBytesSupport().
     *
     * @return true if the read succeeded, false if not. The read can fail
     *              because of the surface doesn't support reading, the color type
     *              is not allowed for the format of the surface or if the rectangle
     *              read is not contained in the surface.
     */
    bool readPixels(GrSurface* surface, int left, int top, int width, int height,
                    GrColorType surfaceColorType, GrColorType dstColorType, void* buffer,
                    size_t rowBytes);

    /**
     * Updates the pixels in a rectangle of a surface.  No sRGB/linear conversions are performed.
     *
     * @param surface           The surface to write to.
     * @param left              left edge of the rectangle to write (inclusive)
     * @param top               top edge of the rectangle to write (inclusive)
     * @param width             width of rectangle to write in pixels.
     * @param height            height of rectangle to write in pixels.
     * @param surfaceColorType  the color type for this use of the surface.
     * @param srcColorType      the color type of the source buffer.
     * @param texels            array of mipmap levels containing texture data. Row bytes must be a
     *                          multiple of srcColorType's bytes-per-pixel. Must be tight to level
     *                          width if !caps->writePixelsRowBytesSupport().
     * @param mipLevelCount     number of levels in 'texels'
     *
     * @return true if the write succeeded, false if not. The read can fail
     *              because of the surface doesn't support writing (e.g. read only),
     *              the color type is not allowed for the format of the surface or
     *              if the rectangle written is not contained in the surface.
     */
    bool writePixels(GrSurface* surface, int left, int top, int width, int height,
                     GrColorType surfaceColorType, GrColorType srcColorType,
                     const GrMipLevel texels[], int mipLevelCount);

    /**
     * Helper for the case of a single level.
     */
    bool writePixels(GrSurface* surface, int left, int top, int width, int height,
                     GrColorType surfaceColorType, GrColorType srcColorType, const void* buffer,
                     size_t rowBytes) {
        GrMipLevel mipLevel = {buffer, rowBytes};
        return this->writePixels(surface, left, top, width, height, surfaceColorType, srcColorType,
                                 &mipLevel, 1);
    }

    /**
     * Updates the pixels in a rectangle of a texture using a buffer. If the texture is MIP mapped,
     * the base level is written to.
     *
     * @param texture          The texture to write to.
     * @param left             left edge of the rectangle to write (inclusive)
     * @param top              top edge of the rectangle to write (inclusive)
     * @param width            width of rectangle to write in pixels.
     * @param height           height of rectangle to write in pixels.
     * @param textureColorType the color type for this use of the surface.
     * @param bufferColorType  the color type of the transfer buffer's pixel data
     * @param transferBuffer   GrBuffer to read pixels from (type must be "kXferCpuToGpu")
     * @param offset           offset from the start of the buffer
     * @param rowBytes         number of bytes between consecutive rows in the buffer. Must be a
     *                         multiple of bufferColorType's bytes-per-pixel. Must be tight to width
     *                         if !caps->writePixelsRowBytesSupport().
     */
    bool transferPixelsTo(GrTexture* texture, int left, int top, int width, int height,
                          GrColorType textureColorType, GrColorType bufferColorType,
                          GrGpuBuffer* transferBuffer, size_t offset, size_t rowBytes);

    /**
     * Reads the pixels from a rectangle of a surface into a buffer. Use
     * GrCaps::SupportedRead::fOffsetAlignmentForTransferBuffer to determine the requirements for
     * the buffer offset alignment. If the surface is a MIP mapped texture, the base level is read.
     *
     * If successful the row bytes in the buffer is always:
     *   GrColorTypeBytesPerPixel(bufferColorType) * width
     *
     * Asserts that the caller has passed a properly aligned offset and that the buffer is
     * large enough to hold the result
     *
     * @param surface          The surface to read from.
     * @param left             left edge of the rectangle to read (inclusive)
     * @param top              top edge of the rectangle to read (inclusive)
     * @param width            width of rectangle to read in pixels.
     * @param height           height of rectangle to read in pixels.
     * @param surfaceColorType the color type for this use of the surface.
     * @param bufferColorType  the color type of the transfer buffer's pixel data
     * @param transferBuffer   GrBuffer to write pixels to (type must be "kXferGpuToCpu")
     * @param offset           offset from the start of the buffer
     */
    bool transferPixelsFrom(GrSurface* surface, int left, int top, int width, int height,
                            GrColorType surfaceColorType, GrColorType bufferColorType,
                            GrGpuBuffer* transferBuffer, size_t offset);

    // Called to perform a surface to surface copy. Fallbacks to issuing a draw from the src to dst
    // take place at the GrOpList level and this function implement faster copy paths. The rect
    // and point are pre-clipped. The src rect and implied dst rect are guaranteed to be within the
    // src/dst bounds and non-empty. They must also be in their exact device space coords, including
    // already being transformed for origin if need be. If canDiscardOutsideDstRect is set to true
    // then we don't need to preserve any data on the dst surface outside of the copy.
    bool copySurface(GrSurface* dst, GrSurface* src, const SkIRect& srcRect,
                     const SkIPoint& dstPoint, bool canDiscardOutsideDstRect = false);

    // Queries the per-pixel HW sample locations for the given render target, and then finds or
    // assigns a key that uniquely identifies the sample pattern. The actual sample locations can be
    // retrieved with retrieveSampleLocations().
    int findOrAssignSamplePatternKey(GrRenderTarget*);

    // Retrieves the per-pixel HW sample locations for the given sample pattern key, and, as a
    // by-product, the actual number of samples in use. (This may differ from the number of samples
    // requested by the render target.) Sample locations are returned as 0..1 offsets relative to
    // the top-left corner of the pixel.
    const SkTArray<SkPoint>& retrieveSampleLocations(int samplePatternKey) const {
        return fSamplePatternDictionary.retrieveSampleLocations(samplePatternKey);
    }

    // Returns a GrGpuRTCommandBuffer which GrOpLists send draw commands to instead of directly
    // to the Gpu object. The 'bounds' rect is the content rect of the destination.
    virtual GrGpuRTCommandBuffer* getCommandBuffer(
            GrRenderTarget*, GrSurfaceOrigin, const SkRect& bounds,
            const GrGpuRTCommandBuffer::LoadAndStoreInfo&,
            const GrGpuRTCommandBuffer::StencilLoadAndStoreInfo&) = 0;

    // Returns a GrGpuTextureCommandBuffer which GrOpLists send texture commands to instead of
    // directly to the Gpu object.
    virtual GrGpuTextureCommandBuffer* getCommandBuffer(GrTexture*, GrSurfaceOrigin) = 0;

    // Called by GrDrawingManager when flushing.
    // Provides a hook for post-flush actions (e.g. Vulkan command buffer submits). This will also
    // insert any numSemaphore semaphores on the gpu and set the backendSemaphores to match the
    // inserted semaphores.
    GrSemaphoresSubmitted finishFlush(GrSurfaceProxy*[], int n,
                                      SkSurface::BackendSurfaceAccess access, const GrFlushInfo&,
                                      const GrPrepareForExternalIORequests&);

    virtual void submit(GrGpuCommandBuffer*) = 0;

    virtual GrFence SK_WARN_UNUSED_RESULT insertFence() = 0;
    virtual bool waitFence(GrFence, uint64_t timeout = 1000) = 0;
    virtual void deleteFence(GrFence) const = 0;

    virtual sk_sp<GrSemaphore> SK_WARN_UNUSED_RESULT makeSemaphore(bool isOwned = true) = 0;
    virtual sk_sp<GrSemaphore> wrapBackendSemaphore(const GrBackendSemaphore& semaphore,
                                                    GrResourceProvider::SemaphoreWrapType wrapType,
                                                    GrWrapOwnership ownership) = 0;
    virtual void insertSemaphore(sk_sp<GrSemaphore> semaphore) = 0;
    virtual void waitSemaphore(sk_sp<GrSemaphore> semaphore) = 0;

    virtual void checkFinishProcs() = 0;

    /**
     *  Put this texture in a safe and known state for use across multiple GrContexts. Depending on
     *  the backend, this may return a GrSemaphore. If so, other contexts should wait on that
     *  semaphore before using this texture.
     */
    virtual sk_sp<GrSemaphore> prepareTextureForCrossContextUsage(GrTexture*) = 0;

    ///////////////////////////////////////////////////////////////////////////
    // Debugging and Stats

    class Stats {
    public:
#if GR_GPU_STATS
        Stats() = default;

        void reset() { *this = {}; }

        int renderTargetBinds() const { return fRenderTargetBinds; }
        void incRenderTargetBinds() { fRenderTargetBinds++; }

        int shaderCompilations() const { return fShaderCompilations; }
        void incShaderCompilations() { fShaderCompilations++; }

        int textureCreates() const { return fTextureCreates; }
        void incTextureCreates() { fTextureCreates++; }

        int textureUploads() const { return fTextureUploads; }
        void incTextureUploads() { fTextureUploads++; }

        int transfersToTexture() const { return fTransfersToTexture; }
        void incTransfersToTexture() { fTransfersToTexture++; }

        int transfersFromSurface() const { return fTransfersFromSurface; }
        void incTransfersFromSurface() { fTransfersFromSurface++; }

        int stencilAttachmentCreates() const { return fStencilAttachmentCreates; }
        void incStencilAttachmentCreates() { fStencilAttachmentCreates++; }

        int numDraws() const { return fNumDraws; }
        void incNumDraws() { fNumDraws++; }

        int numFailedDraws() const { return fNumFailedDraws; }
        void incNumFailedDraws() { ++fNumFailedDraws; }

        int numFinishFlushes() const { return fNumFinishFlushes; }
        void incNumFinishFlushes() { ++fNumFinishFlushes; }

        int numScratchTexturesReused() const { return fNumScratchTexturesReused; }
        void incNumScratchTexturesReused() { ++fNumScratchTexturesReused; }

#if GR_TEST_UTILS
        void dump(SkString*);
        void dumpKeyValuePairs(SkTArray<SkString>* keys, SkTArray<double>* values);
#endif
    private:
        int fRenderTargetBinds = 0;
        int fShaderCompilations = 0;
        int fTextureCreates = 0;
        int fTextureUploads = 0;
        int fTransfersToTexture = 0;
        int fTransfersFromSurface = 0;
        int fStencilAttachmentCreates = 0;
        int fNumDraws = 0;
        int fNumFailedDraws = 0;
        int fNumFinishFlushes = 0;
        int fNumScratchTexturesReused = 0;
#else

#if GR_TEST_UTILS
        void dump(SkString*) {}
        void dumpKeyValuePairs(SkTArray<SkString>*, SkTArray<double>*) {}
#endif
        void incRenderTargetBinds() {}
        void incShaderCompilations() {}
        void incTextureCreates() {}
        void incTextureUploads() {}
        void incTransfersToTexture() {}
        void incStencilAttachmentCreates() {}
        void incNumDraws() {}
        void incNumFailedDraws() {}
        void incNumFinishFlushes() {}
#endif
    };

    Stats* stats() { return &fStats; }
    void dumpJSON(SkJSONWriter*) const;

    /**
     * Creates a texture directly in the backend API without wrapping it in a GrTexture.
     * Must be matched with a call to deleteBackendTexture().
     * Right now, the color is ignored if pixel data is provided.
     * In the future, if neither a color nor pixels are provided then the backend texture
     * will be uninitialized.
     */
    virtual GrBackendTexture createBackendTexture(int w, int h, const GrBackendFormat&,
                                                  GrMipMapped, GrRenderable,
                                                  const void* pixels, size_t rowBytes,
                                                  const SkColor4f* color,
                                                  GrProtected isProtected) = 0;

    /**
     * Frees a texture created by createBackendTexture(). If ownership of the backend
     * texture has been transferred to a GrContext using adopt semantics this should not be called.
     */
    virtual void deleteBackendTexture(const GrBackendTexture&) = 0;

#if GR_TEST_UTILS
    /** Check a handle represents an actual texture in the backend API that has not been freed. */
    virtual bool isTestingOnlyBackendTexture(const GrBackendTexture&) const = 0;

    virtual GrBackendRenderTarget createTestingOnlyBackendRenderTarget(int w, int h,
                                                                       GrColorType) = 0;

    virtual void deleteTestingOnlyBackendRenderTarget(const GrBackendRenderTarget&) = 0;

    // This is only to be used in GL-specific tests.
    virtual const GrGLContext* glContextForTesting() const { return nullptr; }

    // This is only to be used by testing code
    virtual void resetShaderCacheForTesting() const {}

    /**
     * Flushes all work to the gpu and forces the GPU to wait until all the gpu work has completed.
     * This is for testing purposes only.
     */
    virtual void testingOnly_flushGpuAndSync() = 0;
#endif

    // width and height may be larger than rt (if underlying API allows it).
    // Returns nullptr if compatible sb could not be created, otherwise the caller owns the ref on
    // the GrStencilAttachment.
    virtual GrStencilAttachment* createStencilAttachmentForRenderTarget(
            const GrRenderTarget*, int width, int height, int numStencilSamples) = 0;

    // Determines whether a texture will need to be rescaled in order to be used with the
    // GrSamplerState.
    static bool IsACopyNeededForRepeatWrapMode(const GrCaps*, GrTextureProxy* texProxy,
                                               int width, int height,
                                               GrSamplerState::Filter,
                                               GrTextureProducer::CopyParams*,
                                               SkScalar scaleAdjust[2]);

    // Determines whether a texture will need to be copied because the draw requires mips but the
    // texutre doesn't have any. This call should be only checked if IsACopyNeededForTextureParams
    // fails. If the previous call succeeds, then a copy should be done using those params and the
    // mip mapping requirements will be handled there.
    static bool IsACopyNeededForMips(const GrCaps* caps, const GrTextureProxy* texProxy,
                                     GrSamplerState::Filter filter,
                                     GrTextureProducer::CopyParams* copyParams);

    void handleDirtyContext() {
        if (fResetBits) {
            this->resetContext();
        }
    }

    /**
     * Returns a key that represents the sampler that will be created for the passed in parameters.
     * Currently this key is only used when we are building a vulkan pipeline with immutable
     * samplers. In that case, we need our cache key to also contain this key.
     *
     * A return value of 0 indicates that the program/pipeline we are creating is not affected by
     * the sampler.
     */
    virtual uint32_t getExtraSamplerKeyForProgram(const GrSamplerState&, const GrBackendFormat&) {
        return 0;
    }

    virtual void storeVkPipelineCacheData() {}

protected:
    // Handles cases where a surface will be updated without a call to flushRenderTarget.
    void didWriteToSurface(GrSurface* surface, GrSurfaceOrigin origin, const SkIRect* bounds,
                           uint32_t mipLevels = 1) const;

    Stats                            fStats;
    std::unique_ptr<GrPathRendering> fPathRendering;
    // Subclass must initialize this in its constructor.
    sk_sp<const GrCaps>              fCaps;

private:
    // called when the 3D context state is unknown. Subclass should emit any
    // assumed 3D context state and dirty any state cache.
    virtual void onResetContext(uint32_t resetBits) = 0;

    // Implementation of resetTextureBindings.
    virtual void onResetTextureBindings() {}

    // Queries the effective number of samples in use by the hardware for the given render target,
    // and queries the individual sample locations.
    virtual void querySampleLocations(GrRenderTarget*, SkTArray<SkPoint>*) = 0;

    // Called before certain draws in order to guarantee coherent results from dst reads.
    virtual void xferBarrier(GrRenderTarget*, GrXferBarrierType) = 0;

    // overridden by backend-specific derived class to create objects.
    // Texture size and sample size will have already been validated in base class before
    // onCreateTexture is called.
    virtual sk_sp<GrTexture> onCreateTexture(const GrSurfaceDesc&, GrRenderable,
                                             int renderTargetSampleCnt, SkBudgeted, GrProtected,
                                             const GrMipLevel[], int mipLevelCount) = 0;
    virtual sk_sp<GrTexture> onCreateCompressedTexture(int width, int height,
                                                       SkImage::CompressionType, SkBudgeted,
                                                       const void* data) = 0;
    virtual sk_sp<GrTexture> onWrapBackendTexture(const GrBackendTexture&, GrColorType,
                                                  GrWrapOwnership, GrWrapCacheable, GrIOType) = 0;
    virtual sk_sp<GrTexture> onWrapRenderableBackendTexture(const GrBackendTexture&, int sampleCnt,
                                                            GrColorType, GrWrapOwnership,
                                                            GrWrapCacheable) = 0;
    virtual sk_sp<GrRenderTarget> onWrapBackendRenderTarget(const GrBackendRenderTarget&,
                                                            GrColorType) = 0;
    virtual sk_sp<GrRenderTarget> onWrapBackendTextureAsRenderTarget(const GrBackendTexture&,
                                                                     int sampleCnt,
                                                                     GrColorType) = 0;
    virtual sk_sp<GrRenderTarget> onWrapVulkanSecondaryCBAsRenderTarget(const SkImageInfo&,
                                                                        const GrVkDrawableInfo&);

    virtual sk_sp<GrGpuBuffer> onCreateBuffer(size_t size, GrGpuBufferType intendedType,
                                              GrAccessPattern, const void* data) = 0;

    // overridden by backend-specific derived class to perform the surface read
    virtual bool onReadPixels(GrSurface*, int left, int top, int width, int height,
                              GrColorType surfaceColorType, GrColorType dstColorType, void* buffer,
                              size_t rowBytes) = 0;

    // overridden by backend-specific derived class to perform the surface write
    virtual bool onWritePixels(GrSurface*, int left, int top, int width, int height,
                               GrColorType surfaceColorType, GrColorType srcColorType,
                               const GrMipLevel texels[], int mipLevelCount) = 0;

    // overridden by backend-specific derived class to perform the texture transfer
    virtual bool onTransferPixelsTo(GrTexture*, int left, int top, int width, int height,
                                    GrColorType textiueColorType, GrColorType bufferColorType,
                                    GrGpuBuffer* transferBuffer, size_t offset,
                                    size_t rowBytes) = 0;
    // overridden by backend-specific derived class to perform the surface transfer
    virtual bool onTransferPixelsFrom(GrSurface*, int left, int top, int width, int height,
                                      GrColorType surfaceColorType, GrColorType bufferColorType,
                                      GrGpuBuffer* transferBuffer, size_t offset) = 0;

    // overridden by backend-specific derived class to perform the resolve
    virtual void onResolveRenderTarget(GrRenderTarget* target) = 0;

    // overridden by backend specific derived class to perform mip map level regeneration.
    virtual bool onRegenerateMipMapLevels(GrTexture*) = 0;

    // overridden by backend specific derived class to perform the copy surface
    virtual bool onCopySurface(GrSurface* dst, GrSurface* src, const SkIRect& srcRect,
                               const SkIPoint& dstPoint, bool canDiscardOutsideDstRect) = 0;

    virtual void onFinishFlush(GrSurfaceProxy*[], int n, SkSurface::BackendSurfaceAccess access,
                               const GrFlushInfo&, const GrPrepareForExternalIORequests&) = 0;

#ifdef SK_ENABLE_DUMP_GPU
    virtual void onDumpJSON(SkJSONWriter*) const {}
#endif

    void resetContext() {
        this->onResetContext(fResetBits);
        fResetBits = 0;
    }

    uint32_t fResetBits;
    // The context owns us, not vice-versa, so this ptr is not ref'ed by Gpu.
    GrContext* fContext;
    GrSamplePatternDictionary fSamplePatternDictionary;

    friend class GrPathRendering;
    typedef SkRefCnt INHERITED;
};

#endif