Added SkImage::MakeCrossContextFromEncoded

Designed for Flutter's threading architecture, with
an eye to being useful to other clients. Under the
hood, uses a new image generator class to lazily wrap
a texture for multiple GrContexts.

Bug: skia:
Change-Id: I6c37b12c8ab5bce94b91190e5f0beb91d31ae81b
Reviewed-on: https://skia-review.googlesource.com/14180
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>

1 files changed, 72 insertions, 0 deletions

diff --git a/src/gpu/GrBackendTextureImageGenerator.h b/src/gpu/GrBackendTextureImageGenerator.h
new file mode 100644
index 0000000000..2f35895b5b
--- /dev/null
+++ b/src/gpu/GrBackendTextureImageGenerator.h
@@ -0,0 +1,72 @@
+/*
+ * 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 "SkImageGenerator.h"
+
+#include "GrBackendSurface.h"
+#include "SkAtomics.h"
+
+class GrSemaphore;
+
+class GrBackendTextureImageGenerator : public SkImageGenerator {
+public:
+    static std::unique_ptr<SkImageGenerator> Make(sk_sp<GrTexture>, sk_sp<GrSemaphore>,
+                                                  SkAlphaType, sk_sp<SkColorSpace>);
+
+    ~GrBackendTextureImageGenerator();
+
+protected:
+    bool onGetPixels(const SkImageInfo& info, void* pixels, size_t rowBytes, SkPMColor ctable[],
+                     int* ctableCount) override;
+    bool onGetPixels(const SkImageInfo& info, void* pixels, size_t rowBytes, const Options& opts)
+                     override;
+
+#if SK_SUPPORT_GPU
+    sk_sp<GrTextureProxy> onGenerateTexture(GrContext*, const SkImageInfo&,
+                                            const SkIPoint&) override;
+#endif
+
+private:
+    GrBackendTextureImageGenerator(const SkImageInfo& info, GrTexture*,
+                                   uint32_t owningContextID, sk_sp<GrSemaphore>,
+                                   const GrBackendTexture&);
+
+    static void ReleaseRefHelper_TextureReleaseProc(void* ctx);
+
+    class RefHelper : public SkNVRefCnt<RefHelper> {
+    public:
+        RefHelper(GrTexture* texture, uint32_t owningContextID)
+            : fOriginalTexture(texture)
+            , fOwningContextID(owningContextID)
+            , fBorrowedTexture(nullptr)
+            , fBorrowingContextID(SK_InvalidGenID) { }
+
+        ~RefHelper();
+
+        GrTexture* fOriginalTexture;
+        uint32_t fOwningContextID;
+
+        // There is never a 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 lets us
+        // avoid releasing a ref from another thread, or get into races during context shutdown.
+        GrTexture* fBorrowedTexture;
+        SkAtomic<uint32_t> fBorrowingContextID;
+    };
+
+    RefHelper* fRefHelper;
+
+    sk_sp<GrSemaphore> fSemaphore;
+    uint32_t fLastBorrowingContextID;
+
+    GrBackendTexture fBackendTexture;
+    GrSurfaceOrigin fSurfaceOrigin;
+
+    typedef SkImageGenerator INHERITED;
+};
+#endif  // GrBackendTextureImageGenerator_DEFINED