Bug 1074842 - Let SourceSurfaceCGBitmapContext take ownership of the data when DrawTargetCG is destroyed. r=jrmuizel

gfx/2d/DrawTargetCG.cpp

@@ -149,7 +149,13 @@ DrawTargetCG::DrawTargetCG()
 
 DrawTargetCG::~DrawTargetCG()
 {
-  MarkChanged();
+  if (mSnapshot) {
+    if (mSnapshot->refCount() > 1) {
+      // We only need to worry about snapshots that someone else knows about
+      mSnapshot->DrawTargetWillGoAway();
+    }
+    mSnapshot = nullptr;
+  }
 
   // Both of these are OK with nullptr arguments, so we do not
   // need to check (these could be nullptr if Init fails)

gfx/2d/DrawTargetCG.h

@@ -97,6 +97,7 @@ class DrawTargetCG : public DrawTarget
 public:
   MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(DrawTargetCG)
   friend class BorrowedCGContext;
+  friend class SourceSurfaceCGBitmapContext;
   DrawTargetCG();
   virtual ~DrawTargetCG();
 

gfx/2d/SourceSurfaceCG.cpp

@@ -360,6 +360,24 @@ SourceSurfaceCGBitmapContext::DrawTargetWillChange()
   }
 }
 
+void
+SourceSurfaceCGBitmapContext::DrawTargetWillGoAway()
+{
+  if (mDrawTarget) {
+    if (mDrawTarget->mData != CGBitmapContextGetData(mCg)) {
+      DrawTargetWillChange();
+      return;
+    }
+
+    // Instead of copying the data over, we can just swap it.
+    mDataHolder.Swap(mDrawTarget->mData);
+    mData = mDataHolder;
+    mCg = nullptr;
+    mDrawTarget = nullptr;
+    // mImage is still valid because it still points to the same data.
+  }
+}
+
 SourceSurfaceCGBitmapContext::~SourceSurfaceCGBitmapContext()
 {
   if (mImage)

gfx/2d/SourceSurfaceCG.h

@@ -101,6 +101,7 @@ class SourceSurfaceCGContext : public DataSourceSurface
 public:
   MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(DataSourceSurfaceCGContext)
   virtual void DrawTargetWillChange() = 0;
+  virtual void DrawTargetWillGoAway() = 0;
   virtual CGImageRef GetImage() = 0;
 };
 
@@ -139,6 +140,7 @@ private:
   //XXX: do the other backends friend their DrawTarget?
   friend class DrawTargetCG;
   virtual void DrawTargetWillChange();
+  virtual void DrawTargetWillGoAway();
   void EnsureImage() const;
 
   // We hold a weak reference to these two objects.
@@ -181,6 +183,7 @@ private:
   //XXX: do the other backends friend their DrawTarget?
   friend class DrawTargetCG;
   virtual void DrawTargetWillChange();
+  virtual void DrawTargetWillGoAway() { DrawTargetWillChange(); }
   void EnsureImage() const;
 
   SurfaceFormat mFormat;

gfx/2d/Tools.h

@@ -7,6 +7,7 @@
 #define MOZILLA_GFX_TOOLS_H_
 
 #include "mozilla/CheckedInt.h"
+#include "mozilla/Move.h"
 #include "mozilla/TypeTraits.h"
 #include "Types.h"
 #include "Point.h"
@@ -178,6 +179,13 @@ struct AlignedArray
     mCount = aCount;
   }
 
+  void Swap(AlignedArray<T, alignment>& aOther)
+  {
+    mozilla::Swap(mPtr, aOther.mPtr);
+    mozilla::Swap(mStorage, aOther.mStorage);
+    mozilla::Swap(mCount, aOther.mCount);
+  }
+
   MOZ_ALWAYS_INLINE operator T*()
   {
     return mPtr;