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 "GrCaps.h"
#include "GrGpuCommandBuffer.h"
#include "GrProgramDesc.h"
#include "GrSwizzle.h"
#include "GrAllocator.h"
#include "GrTextureProducer.h"
#include "GrTypes.h"
#include "GrXferProcessor.h"
#include "SkPath.h"
#include "SkTArray.h"
#include <map>

class GrBackendRenderTarget;
class GrBackendSemaphore;
class GrBuffer;
class GrContext;
struct GrContextOptions;
class GrGLContext;
class GrMesh;
class GrPath;
class GrPathRange;
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:
    /**
     * Create an instance of GrGpu that matches the specified backend. If the requested backend is
     * not supported (at compile-time or run-time) this returns nullptr. The context will not be
     * fully constructed and should not be used by GrGpu until after this function returns.
     */
    static sk_sp<GrGpu> Make(GrBackend, GrBackendContext, const GrContextOptions&, GrContext*);

    ////////////////////////////////////////////////////////////////////////////

    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 kRenderTarget_GrSurfaceFlag the 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 budgeted       does this texture count against the resource cache budget?
     * @param texels         array of mipmap levels containing texel data to load.
     *                       Each level begins with full-size palette data for paletted textures.
     *                       It contains width*height texels. If there is only one
     *                       element and it contains nullptr fPixels, texture data is
     *                       uninitialized.
     * @param mipLevelCount  the number of levels in 'texels'
     * @return  The texture object if successful, otherwise nullptr.
     */
    sk_sp<GrTexture> createTexture(const GrSurfaceDesc&, SkBudgeted, const GrMipLevel texels[],
                                   int mipLevelCount);

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

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

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

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

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

    /**
     * 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.
     */
    GrBuffer* createBuffer(size_t size, GrBufferType intendedType, GrAccessPattern accessPattern,
                           const void* data = nullptr);

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

    /** Info struct returned by getReadPixelsInfo about performing intermediate draws before
        reading pixels for performance or correctness. */
    struct ReadPixelTempDrawInfo {
        /**
         * If the GrGpu is requesting that the caller do a draw to an intermediate surface then
         * this is descriptor for the temp surface. The draw should always be a rect with dst
         * 0,0,w,h.
         */
        GrSurfaceDesc   fTempSurfaceDesc;
        /**
         * Indicates whether there is a performance advantage to using an exact match texture
         * (in terms of width and height) for the intermediate texture instead of approximate.
         */
        SkBackingFit    fTempSurfaceFit;
        /**
         * Swizzle to apply during the draw. This is used to compensate for either feature or
         * performance limitations in the underlying 3D API.
         */
        GrSwizzle       fSwizzle;
        /**
         * The color type that should be used to read from the temp surface after the draw. This
         * may be different than the original read color type in order to compensate for swizzling.
         * The read data will effectively be in the original color type. The original gamma
         * encoding is always used.
         */
        GrColorType     fReadColorType;
    };

    /** Describes why an intermediate draw must/should be performed before readPixels. */
    enum DrawPreference {
        /**
         * On input means that the caller would proceed without draw if the GrGpu doesn't request
         * one. On output means that the GrGpu is not requesting a draw.
         */
        kNoDraw_DrawPreference,
        /**
         * Means that the client would prefer a draw for performance of the readback but
         * can satisfy a straight readPixels call on the inputs without an intermediate draw.
         * getReadPixelsInfo will never set the draw preference to this value but may leave
         * it set.
         */
        kCallerPrefersDraw_DrawPreference,
        /**
         * On output means that GrGpu would prefer a draw for performance of the readback but
         * can satisfy a straight readPixels call on the inputs without an intermediate draw. The
         * caller of getReadPixelsInfo should never specify this on intput.
         */
        kGpuPrefersDraw_DrawPreference,
        /**
         * On input means that the caller requires a draw to do a transformation and there is no
         * CPU fallback. On output means that GrGpu can only satisfy the readPixels request if the
         * intermediate draw is performed.
         */
        kRequireDraw_DrawPreference
    };

    /**
     * Used to negotiate whether and how an intermediate draw should or must be performed before
     * a readPixels call. If this returns false then GrGpu could not deduce an intermediate draw
     * that would allow a successful readPixels call. The passed width, height, and rowBytes,
     * must be non-zero and already reflect clipping to the src bounds.
     */
    bool getReadPixelsInfo(GrSurface*, GrSurfaceOrigin, int width, int height, size_t rowBytes,
                           GrColorType, GrSRGBConversion, DrawPreference*, ReadPixelTempDrawInfo*);

    /**
     * Info struct returned by getWritePixelsInfo about performing an intermediate draw in order
     * to write pixels to a GrSurface for either performance or correctness reasons.
     */
    struct WritePixelTempDrawInfo {
        /**
         * If the GrGpu is requesting that the caller upload to an intermediate surface and draw
         * that to the dst then this is the descriptor for the intermediate surface. The caller
         * should upload the pixels such that the upper left pixel of the upload rect is at 0,0 in
         * the intermediate surface
         */
        GrSurfaceDesc   fTempSurfaceDesc;
        /**
         * Swizzle to apply during the draw. This is used to compensate for either feature or
         * performance limitations in the underlying 3D API.
         */
        GrSwizzle       fSwizzle;
        /**
         * The color type that should be specified when uploading the *original* data to the temp
         * surface before the draw. This may be different than the original src color type in
         * order to compensate for swizzling that will occur when drawing. The original gamma
         * encoding is always used.
         */
        GrColorType     fWriteColorType;
    };

    /**
     * Used to negotiate whether and how an intermediate surface should be used to write pixels to
     * a GrSurface. If this returns false then GrGpu could not deduce an intermediate draw
     * that would allow a successful transfer of the src pixels to the dst. The passed width,
     * height, and rowBytes, must be non-zero and already reflect clipping to the dst bounds.
     */
    bool getWritePixelsInfo(GrSurface*, GrSurfaceOrigin, int width, int height, GrColorType,
                            GrSRGBConversion, DrawPreference*, WritePixelTempDrawInfo*);

    /**
     * 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 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. Zero
     *                      means rows are tightly packed.
     * @param invertY       buffer should be populated bottom-to-top as opposed
     *                      to top-to-bottom (skia's usual order)
     *
     * @return true if the read succeeded, false if not. The read can fail
     *              because of a unsupported pixel config or because no render
     *              target is currently set.
     */
    bool readPixels(GrSurface* surface, GrSurfaceOrigin, int left, int top, int width, int height,
                    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 srcColorType  the color type of the source buffer.
     * @param texels        array of mipmap levels containing texture data
     * @param mipLevelCount number of levels in 'texels'
     */
    bool writePixels(GrSurface* surface, GrSurfaceOrigin origin, int left, int top, int width,
                     int height, GrColorType srcColorType, const GrMipLevel texels[],
                     int mipLevelCount);

    /**
     * This function is a shim which creates a SkTArray<GrMipLevel> of size 1.
     * It then calls writePixels with that SkTArray.
     */
    bool writePixels(GrSurface*, GrSurfaceOrigin, int left, int top, int width, int height,
                     GrColorType, const void* buffer, size_t rowBytes);

    /**
     * This version of writePixels doesn't take an origin. TODO: Remove origin handling from
     * GrGpu::writePixels entirely.
     */
    bool writePixels(GrSurface* surface, int left, int top, int width, int height,
                     GrColorType srcColorType, const void* buffer, size_t rowBytes) {
        return this->writePixels(surface, kTopLeft_GrSurfaceOrigin, left, top, width, height,
                                 srcColorType, buffer, rowBytes);
    }

    /**
     * Updates the pixels in a rectangle of a texture using a buffer
     *
     * There are a couple of assumptions here. First, we only update the top miplevel.
     * And second, that any y flip needed has already been done in the buffer.
     *
     * @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 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. Zero
     *                         means rows are tightly packed.
     */
    bool transferPixels(GrTexture* texture, int left, int top, int width, int height,
                        GrColorType bufferColorType, GrBuffer* transferBuffer, size_t offset,
                        size_t rowBytes);

    // After the client interacts directly with the 3D context state the GrGpu
    // must resync its internal state and assumptions about 3D context state.
    // Each time this occurs the GrGpu bumps a timestamp.
    // state of the 3D context
    // At 10 resets / frame and 60fps a 64bit timestamp will overflow in about
    // a billion years.
    typedef uint64_t ResetTimestamp;

    // This timestamp is always older than the current timestamp
    static const ResetTimestamp kExpiredTimestamp = 0;
    // Returns a timestamp based on the number of times the context was reset.
    // This timestamp can be used to lazily detect when cached 3D context state
    // is dirty.
    ResetTimestamp getResetTimestamp() const { return fResetTimestamp; }

    // 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.
    bool copySurface(GrSurface* dst, GrSurfaceOrigin dstOrigin,
                     GrSurface* src, GrSurfaceOrigin srcOrigin,
                     const SkIRect& srcRect,
                     const SkIPoint& dstPoint);

    // Creates a GrGpuRTCommandBuffer which GrOpLists send draw commands to instead of directly
    // to the Gpu object.
    virtual GrGpuRTCommandBuffer* createCommandBuffer(
            GrRenderTarget*, GrSurfaceOrigin,
            const GrGpuRTCommandBuffer::LoadAndStoreInfo&,
            const GrGpuRTCommandBuffer::StencilLoadAndStoreInfo&) = 0;

    // Creates a GrGpuTextureCommandBuffer which GrOpLists send texture commands to instead of
    // directly to the Gpu object.
    virtual GrGpuTextureCommandBuffer* createCommandBuffer(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(int numSemaphores, GrBackendSemaphore backendSemaphores[]);

    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, bool flush = false) = 0;
    virtual void waitSemaphore(sk_sp<GrSemaphore> semaphore) = 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() { this->reset(); }

        void reset() {
            fRenderTargetBinds = 0;
            fShaderCompilations = 0;
            fTextureCreates = 0;
            fTextureUploads = 0;
            fTransfersToTexture = 0;
            fStencilAttachmentCreates = 0;
            fNumDraws = 0;
            fNumFailedDraws = 0;
        }

        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++; }
        void incStencilAttachmentCreates() { fStencilAttachmentCreates++; }
        void incNumDraws() { fNumDraws++; }
        void incNumFailedDraws() { ++fNumFailedDraws; }
        void dump(SkString*);
        void dumpKeyValuePairs(SkTArray<SkString>* keys, SkTArray<double>* values);
        int numDraws() const { return fNumDraws; }
        int numFailedDraws() const { return fNumFailedDraws; }
    private:
        int fRenderTargetBinds;
        int fShaderCompilations;
        int fTextureCreates;
        int fTextureUploads;
        int fTransfersToTexture;
        int fStencilAttachmentCreates;
        int fNumDraws;
        int fNumFailedDraws;
#else
        void dump(SkString*) {}
        void dumpKeyValuePairs(SkTArray<SkString>*, SkTArray<double>*) {}
        void incRenderTargetBinds() {}
        void incShaderCompilations() {}
        void incTextureCreates() {}
        void incTextureUploads() {}
        void incTransfersToTexture() {}
        void incStencilAttachmentCreates() {}
        void incNumDraws() {}
        void incNumFailedDraws() {}
#endif
    };

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

#if GR_TEST_UTILS
    /** Creates a texture directly in the backend API without wrapping it in a GrTexture. This is
        only to be used for testing (particularly for testing the methods that import an externally
        created texture into Skia. Must be matched with a call to deleteTestingOnlyTexture(). */
    GrBackendTexture createTestingOnlyBackendTexture(void* pixels, int w, int h, SkColorType,
                                                     bool isRenderTarget, GrMipMapped);
    /** Older version based on GrPixelConfig. Currently the preferred one above devolves to this. */
    virtual GrBackendTexture createTestingOnlyBackendTexture(
                                                      void* pixels, int w, int h,
                                                      GrPixelConfig config,
                                                      bool isRenderTarget,
                                                      GrMipMapped mipMapped) = 0;
    /** Check a handle represents an actual texture in the backend API that has not been freed. */
    virtual bool isTestingOnlyBackendTexture(const GrBackendTexture&) const = 0;
    /**
     * Frees a texture created by createTestingOnlyBackendTexture(). If ownership of the backend
     * texture has been transferred to a GrContext using adopt semantics this should not be called.
     */
    virtual void deleteTestingOnlyBackendTexture(const GrBackendTexture&) = 0;

    virtual GrBackendRenderTarget createTestingOnlyBackendRenderTarget(int w, int h, GrColorType,
                                                                       GrSRGBEncoded) = 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) = 0;
    // clears target's entire stencil buffer to 0
    virtual void clearStencil(GrRenderTarget* target, int clearValue) = 0;

    // Determines whether a texture will need to be rescaled in order to be used with the
    // GrSamplerState. This variation is called when the caller will create a new texture using the
    // resource provider from a non-texture src (cpu-backed image, ...).
    static bool IsACopyNeededForTextureParams(const GrCaps*, int width, int height,
                                              const GrSamplerState&, GrTextureProducer::CopyParams*,
                                              SkScalar scaleAdjust[2]);

    // Like the above but this variation should be called when the caller is not creating the
    // original texture but rather was handed the original texture. It adds additional checks
    // relevant to original textures that were created external to Skia via
    // GrResourceProvider::wrap methods.
    bool isACopyNeededForTextureParams(GrTextureProxy* proxy, const GrSamplerState& params,
                                       GrTextureProducer::CopyParams* copyParams,
                                       SkScalar scaleAdjust[2]) const {
        if (IsACopyNeededForTextureParams(this->caps(), proxy->width(), proxy->height(), params,
                                          copyParams, scaleAdjust)) {
            return true;
        }
        return this->onIsACopyNeededForTextureParams(proxy, params, copyParams, scaleAdjust);
    }

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

protected:
    static void ElevateDrawPreference(GrGpu::DrawPreference* preference,
                                      GrGpu::DrawPreference elevation) {
        GR_STATIC_ASSERT(GrGpu::kCallerPrefersDraw_DrawPreference > GrGpu::kNoDraw_DrawPreference);
        GR_STATIC_ASSERT(GrGpu::kGpuPrefersDraw_DrawPreference >
                         GrGpu::kCallerPrefersDraw_DrawPreference);
        GR_STATIC_ASSERT(GrGpu::kRequireDraw_DrawPreference >
                         GrGpu::kGpuPrefersDraw_DrawPreference);
        *preference = SkTMax(*preference, elevation);
    }

    // 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;

    typedef SkTArray<SkPoint, true> SamplePattern;

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;

    // 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&, SkBudgeted,
                                             const GrMipLevel texels[], int mipLevelCount) = 0;

    virtual sk_sp<GrTexture> onWrapBackendTexture(const GrBackendTexture&, GrWrapOwnership) = 0;
    virtual sk_sp<GrTexture> onWrapRenderableBackendTexture(const GrBackendTexture&,
                                                            int sampleCnt,
                                                            GrWrapOwnership) = 0;
    virtual sk_sp<GrRenderTarget> onWrapBackendRenderTarget(const GrBackendRenderTarget&) = 0;
    virtual sk_sp<GrRenderTarget> onWrapBackendTextureAsRenderTarget(const GrBackendTexture&,
                                                                     int sampleCnt) = 0;
    virtual GrBuffer* onCreateBuffer(size_t size, GrBufferType intendedType, GrAccessPattern,
                                     const void* data) = 0;

    virtual bool onIsACopyNeededForTextureParams(GrTextureProxy* proxy, const GrSamplerState&,
                                                 GrTextureProducer::CopyParams*,
                                                 SkScalar scaleAdjust[2]) const {
        return false;
    }

    virtual bool onGetReadPixelsInfo(GrSurface*, GrSurfaceOrigin, int width, int height,
                                     size_t rowBytes, GrColorType, DrawPreference*,
                                     ReadPixelTempDrawInfo*) = 0;
    virtual bool onGetWritePixelsInfo(GrSurface*, GrSurfaceOrigin, int width, int height,
                                      GrColorType, DrawPreference*, WritePixelTempDrawInfo*) = 0;

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

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

    // overridden by backend-specific derived class to perform the texture transfer
    virtual bool onTransferPixels(GrTexture*, int left, int top, int width, int height,
                                  GrColorType colorType, GrBuffer* transferBuffer, size_t offset,
                                  size_t rowBytes) = 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 the copy surface
    virtual bool onCopySurface(GrSurface* dst, GrSurfaceOrigin dstOrigin,
                               GrSurface* src, GrSurfaceOrigin srcOrigin,
                               const SkIRect& srcRect, const SkIPoint& dstPoint) = 0;

    virtual void onFinishFlush(bool insertedSemaphores) = 0;

    virtual void onDumpJSON(SkJSONWriter*) const {}

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

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

    friend class GrPathRendering;
    typedef SkRefCnt INHERITED;
};

#endif