Implement SkGLContext swapBuffers with fence syncs

include/gpu/gl/SkGLContext.h

 
 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef SkGLContext_DEFINED
 #define SkGLContext_DEFINED
 
 #include "GrGLInterface.h"
+#include "../../src/gpu/SkGpuFenceSync.h"
 
 /**
  * Create an offscreen opengl context with an RGBA8 / 8bit stencil FBO.
  * Provides a GrGLInterface struct of function pointers for the context.
  */
 
 class SK_API SkGLContext : public SkRefCnt {
 public:
     SK_DECLARE_INST_COUNT(SkGLContext)
 
     ~SkGLContext() override;
 
     bool isValid() const { return NULL != gl(); }
 
     const GrGLInterface* gl() const { return fGL.get(); }
 
-    virtual void makeCurrent() const = 0;
+    bool fenceSyncSupport() const { return SkToBool(fFenceSync); }
+
+    bool getMaxGpuFrameLag(int* maxFrameLag) const {
+        if (!fFenceSync) {
+            return false;
+        }
+        *maxFrameLag = kMaxFrameLag;
+        return true;
+    }
+
+    void makeCurrent() const;
 
     /**
-     * The primary purpose of this function it to provide a means of scheduling
+     * The only purpose of this function it to provide a means of scheduling
      * work on the GPU (since all of the subclasses create primary buffers for
      * testing that are small and not meant to be rendered to the screen).
      *
-     * If the drawing surface provided by the platform is double buffered this
-     * call will cause the platform to swap which buffer is currently being
-     * targeted.  If the current surface does not include a back buffer, this
-     * call has no effect.
+     * If the platform supports fence sync (OpenGL 3.2+ or EGL_KHR_fence_sync),
+     * this will not swap any buffers, but rather emulate triple buffer
+     * synchronization using fences.
+     *
+     * Otherwise it will call the platform SwapBuffers method. This may or may
+     * not perform some sort of synchronization, depending on whether the
+     * drawing surface provided by the platform is double buffered.
      */
-    virtual void swapBuffers() const = 0;
+    void swapBuffers();
 
     /**
      * This notifies the context that we are deliberately testing abandoning
      * the context. It is useful for debugging contexts that would otherwise
      * test that GPU resources are properly deleted. It also allows a debugging
      * context to test that further GL calls are not made by Skia GPU code.
      */
     void testAbandon();
 
+    class GLFenceSync;  // SkGpuFenceSync implementation that uses the OpenGL functionality.
+
 protected:
     SkGLContext();
 
+    /*
+     * Methods that sublcasses must call from their constructors and destructors.
+     */
+    void init(const GrGLInterface*, SkGpuFenceSync* = NULL);
+    void teardown();
+
+    /*
+     * Operations that have a platform-dependent implementation.
+     */
+    virtual void onPlatformMakeCurrent() const = 0;
+    virtual void onPlatformSwapBuffers() const = 0;
+    virtual GrGLFuncPtr onPlatformGetProcAddress(const char*) const = 0;
+
+private:
+    enum { kMaxFrameLag = 3 };
+
+    SkAutoTDelete<SkGpuFenceSync> fFenceSync;
+    SkPlatformGpuFence            fFrameFences[kMaxFrameLag - 1];
+    int                           fCurrentFenceIdx;
+
     /** Subclass provides the gl interface object if construction was
      *  successful. */
     SkAutoTUnref<const GrGLInterface> fGL;
 
+    friend class GLFenceSync;  // For onPlatformGetProcAddress.
+
     typedef SkRefCnt INHERITED;
 };
 
 /** Creates platform-dependent GL context object
  * Returns a valid gl context object or NULL if such can not be created.
  * Note: If Skia embedder needs a custom GL context that sets up the GL
  * interface, this function should be implemented by the embedder.
  * Otherwise, the default implementation for the platform should be compiled in
  * the library.
  */
 SK_API SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI);
 
 /**
  * Helper macros for using the GL context through the GrGLInterface. Example:
  * SK_GL(glCtx, GenTextures(1, &texID));
  */
 #define SK_GL(ctx, X) (ctx).gl()->fFunctions.f ## X;    \
                       SkASSERT(0 == (ctx).gl()->fFunctions.fGetError())
 #define SK_GL_RET(ctx, RET, X) (RET) = (ctx).gl()->fFunctions.f ## X;    \
                   SkASSERT(0 == (ctx).gl()->fFunctions.fGetError())
 #define SK_GL_NOERRCHECK(ctx, X) (ctx).gl()->fFunctions.f ## X
 #define SK_GL_RET_NOERRCHECK(ctx, RET, X) (RET) = (ctx).gl()->fFunctions.f ## X
 
 #endif