GrBackendTextureImageGenerator.h

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/*
 * Copyright 2017 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
#ifndef GrBackendTextureImageGenerator_DEFINED
#define GrBackendTextureImageGenerator_DEFINED
 
#include "include/core/SkImageGenerator.h"
#include "include/gpu/GrBackendSurface.h"
#include "include/gpu/GrDirectContext.h"
#include "include/private/base/SkMutex.h"
#include "include/private/gpu/ganesh/GrTextureGenerator.h"
#include "src/gpu/ResourceKey.h"
#include "src/gpu/ganesh/GrSurfaceProxyView.h"
#include "src/gpu/ganesh/GrTexture.h"
 
class GrSemaphore;
 
/*
 * This ImageGenerator is used to wrap a texture in one GrContext and can then be used as a source
 * in another GrContext. It holds onto a semaphore which the producing GrContext will signal and the
 * consuming GrContext will wait on before using the texture. Only one GrContext can ever be used
 * as a consumer (this is mostly because Vulkan can't allow multiple things to wait on the same
 * semaphore).
 *
 * In practice, this capability is used by clients to create backend-specific texture resources in
 * one thread (with, say, GrContext-A) and then ship them over to another GrContext (say,
 * GrContext-B) which will then use the texture as a source for draws. GrContext-A uses the
 * semaphore to notify GrContext-B when the shared texture is ready to use.
 */
class GrBackendTextureImageGenerator : public GrTextureGenerator {
public:
    static std::unique_ptr<GrTextureGenerator> Make(const sk_sp<GrTexture>&, GrSurfaceOrigin,
                                                    std::unique_ptr<GrSemaphore>, SkColorType,
                                                    SkAlphaType, sk_sp<SkColorSpace>);
 
    ~GrBackendTextureImageGenerator() override;
 
protected:
    bool onIsValid(GrRecordingContext* context) const override {
        if (context && context->abandoned()) {
            return false;
        }
        return true;
    }
    bool onIsProtected() const override;
 
    GrSurfaceProxyView onGenerateTexture(GrRecordingContext*,
                                         const SkImageInfo&,
                                         skgpu::Mipmapped mipmapped,
                                         GrImageTexGenPolicy) override;
 
private:
    GrBackendTextureImageGenerator(const SkColorInfo&,
                                   const sk_sp<GrTexture>&,
                                   GrSurfaceOrigin,
                                   GrDirectContext::DirectContextID owningContextID,
                                   std::unique_ptr<GrSemaphore>);
 
    static void ReleaseRefHelper_TextureReleaseProc(void* ctx);
 
    class RefHelper : public SkNVRefCnt<RefHelper> {
    public:
        RefHelper(sk_sp<GrTexture>,
                  GrDirectContext::DirectContextID owningContextID,
                  std::unique_ptr<GrSemaphore>);
 
        ~RefHelper();
 
        sk_sp<GrTexture>                 fOriginalTexture;
        GrDirectContext::DirectContextID fOwningContextID;
 
        // We use this key so that we don't rewrap the GrBackendTexture in a GrTexture for each
        // proxy created from this generator for a particular borrowing context.
        skgpu::UniqueKey                 fBorrowedTextureKey;
        // There is no ref associated with this pointer. We rely on our atomic bookkeeping with the
        // context ID to know when this pointer is valid and safe to use. This is used to make sure
        // all uses of the wrapped texture are finished on the borrowing context before we open
        // this back up to other contexts. In general a ref to this release proc is owned by all
        // proxies and gpu uses of the backend texture.
        skgpu::RefCntedCallback*         fBorrowingContextReleaseProc;
        GrDirectContext::DirectContextID fBorrowingContextID;
 
        std::unique_ptr<GrSemaphore>     fSemaphore;
    };
 
    RefHelper*       fRefHelper;
    // This Mutex is used to guard the borrowing of the texture to one GrContext at a time as well
    // as the creation of the fBorrowingContextReleaseProc. The latter happening if two threads with
    // the same consuming GrContext try to generate a texture at the same time.
    SkMutex          fBorrowingMutex;
 
    GrBackendTexture fBackendTexture;
    GrSurfaceOrigin  fSurfaceOrigin;
 
    using INHERITED = GrTextureGenerator;
};
#endif  // GrBackendTextureImageGenerator_DEFINED