Loosen requirement that there be only one GrDrawTarget

include/gpu/GrRenderTarget.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 GrRenderTarget_DEFINED
 #define GrRenderTarget_DEFINED
 
 #include "GrSurface.h"
 #include "SkRect.h"
 
+class GrDrawTarget;
 class GrStencilAttachment;
 class GrRenderTargetPriv;
 
 /**
  * GrRenderTarget represents a 2D buffer of pixels that can be rendered to.
  * A context's render target is set by setRenderTarget(). Render targets are
  * created by a createTexture with the kRenderTarget_SurfaceFlag flag.
  * Additionally, GrContext provides methods for creating GrRenderTargets
  * that wrap externally created render targets.
  */
@@ skipping 120 matching lines @@
      */
     virtual GrBackendObject getRenderTargetHandle() const = 0;
 
     // Checked when this object is asked to attach a stencil buffer.
     virtual bool canAttemptStencilAttachment() const = 0;
 
     // Provides access to functions that aren't part of the public API.
     GrRenderTargetPriv renderTargetPriv();
     const GrRenderTargetPriv renderTargetPriv() const;
 
+    void setLastDrawTarget(GrDrawTarget* dt);
+    GrDrawTarget* getLastDrawTarget() { return fLastDrawTarget; }
+
 protected:
     GrRenderTarget(GrGpu* gpu, LifeCycle lifeCycle, const GrSurfaceDesc& desc,
                    SampleConfig sampleConfig, GrStencilAttachment* stencil = nullptr)
         : INHERITED(gpu, lifeCycle, desc)
         , fStencilAttachment(stencil)
-        , fSampleConfig(sampleConfig) {
+        , fSampleConfig(sampleConfig)
+        , fLastDrawTarget(nullptr) {
         fResolveRect.setLargestInverted();
     }
 
     // override of GrResource
     void onAbandon() override;
     void onRelease() override;
 
 private:
     // Allows the backends to perform any additional work that is required for attaching a
     // GrStencilAttachment. When this is called, the GrStencilAttachment has already been put onto
     // the GrRenderTarget. This function must return false if any failures occur when completing the
     // stencil attachment.
     virtual bool completeStencilAttachment() = 0;
 
     friend class GrRenderTargetPriv;
 
     GrStencilAttachment*  fStencilAttachment;
     SampleConfig          fSampleConfig;
 
     SkIRect               fResolveRect;
 
+    // The last drawTarget that wrote to or is currently going to write to this renderTarget
+    // The drawTarget can be closed (e.g., no draw context is currently bound
+    // to this renderTarget).
+    // This back-pointer is required so that we can add a dependancy between
+    // the drawTarget used to create the current contents of this renderTarget
+    // and the drawTarget of a destination renderTarget to which this one is being drawn.
+    GrDrawTarget* fLastDrawTarget;
+
     typedef GrSurface INHERITED;
 };
 
 
 #endif