From 9d0fbfa02c72538f3d6f4e99e5f9d3d74fc22006 Mon Sep 17 00:00:00 2001
From: Markus Stange <mstange@themasta.com>
Date: Fri, 24 Oct 2014 18:32:22 +0200
Subject: [PATCH] Bug 1074842 - Let SourceSurfaceCGBitmapContext take ownership
 of the data when DrawTargetCG is destroyed. r=jrmuizel

---
 gfx/2d/DrawTargetCG.cpp    |  8 +++++++-
 gfx/2d/DrawTargetCG.h      |  1 +
 gfx/2d/SourceSurfaceCG.cpp | 18 ++++++++++++++++++
 gfx/2d/SourceSurfaceCG.h   |  3 +++
 gfx/2d/Tools.h             |  8 ++++++++
 5 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/gfx/2d/DrawTargetCG.cpp b/gfx/2d/DrawTargetCG.cpp
index bea930b2126c..d42920c4cc4e 100644
--- a/gfx/2d/DrawTargetCG.cpp
+++ b/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)
diff --git a/gfx/2d/DrawTargetCG.h b/gfx/2d/DrawTargetCG.h
index 4284c495d2dc..382d9f77f2ca 100644
--- a/gfx/2d/DrawTargetCG.h
+++ b/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();
 
diff --git a/gfx/2d/SourceSurfaceCG.cpp b/gfx/2d/SourceSurfaceCG.cpp
index 49def436c064..12b038c20d9e 100644
--- a/gfx/2d/SourceSurfaceCG.cpp
+++ b/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)
diff --git a/gfx/2d/SourceSurfaceCG.h b/gfx/2d/SourceSurfaceCG.h
index 24529e399a87..9e1798490e71 100644
--- a/gfx/2d/SourceSurfaceCG.h
+++ b/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;
diff --git a/gfx/2d/Tools.h b/gfx/2d/Tools.h
index 0cde7d6d4d40..d7405c75bce6 100644
--- a/gfx/2d/Tools.h
+++ b/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;