Bug 1057894 (Part 2) - Add RAII smart handles for imgFrame locking. r=tn

image/src/imgFrame.cpp

@@ -312,6 +312,18 @@ nsresult imgFrame::Optimize()
   return NS_OK;
 }
 
+DrawableFrameRef
+imgFrame::DrawableRef()
+{
+  return DrawableFrameRef(this);
+}
+
+RawAccessFrameRef
+imgFrame::RawAccessRef()
+{
+  return RawAccessFrameRef(this);
+}
+
 imgFrame::SurfaceWithFormat
 imgFrame::SurfaceForDrawing(bool               aDoPadding,
                             bool               aDoPartialDecode,

image/src/imgFrame.h

@@ -8,6 +8,7 @@
 #define imgFrame_h
 
 #include "mozilla/MemoryReporting.h"
+#include "mozilla/Move.h"
 #include "mozilla/Mutex.h"
 #include "mozilla/VolatileBuffer.h"
 #include "gfxDrawable.h"
@@ -17,6 +18,8 @@ namespace mozilla {
 namespace image {
 
 class ImageRegion;
+class DrawableFrameRef;
+class RawAccessFrameRef;
 
 class imgFrame
 {
@@ -36,6 +39,9 @@ public:
   nsresult Init(int32_t aX, int32_t aY, int32_t aWidth, int32_t aHeight, SurfaceFormat aFormat, uint8_t aPaletteDepth = 0);
   nsresult Optimize();
 
+  DrawableFrameRef DrawableRef();
+  RawAccessFrameRef RawAccessRef();
+
   bool Draw(gfxContext* aContext, const ImageRegion& aRegion,
             const nsIntMargin& aPadding, GraphicsFilter aFilter,
             uint32_t aImageFlags);
@@ -165,31 +171,165 @@ private: // data
 
   /** Have we called DiscardTracker::InformAllocation()? */
   bool mInformedDiscardTracker;
+
+  friend class DrawableFrameRef;
+  friend class RawAccessFrameRef;
 };
 
-  // An RAII class to ensure it's easy to balance locks and unlocks on
-  // imgFrames.
-  class AutoFrameLocker
+/**
+ * A reference to an imgFrame that holds the imgFrame's surface in memory,
+ * allowing drawing. If you have a DrawableFrameRef |ref| and |if (ref)| returns
+ * true, then calls to Draw() and GetSurface() are guaranteed to succeed.
+ */
+class DrawableFrameRef MOZ_FINAL
 {
+  // Implementation details for safe boolean conversion.
+  typedef void (DrawableFrameRef::* ConvertibleToBool)(float*****, double*****);
+  void nonNull(float*****, double*****) {}
+
 public:
-    explicit AutoFrameLocker(imgFrame* frame)
-      : mFrame(frame)
-      , mSucceeded(NS_SUCCEEDED(frame->LockImageData()))
+  DrawableFrameRef() { }
+
+  explicit DrawableFrameRef(imgFrame* aFrame)
+    : mFrame(aFrame)
+    , mRef(aFrame->mVBuf)
+  {
+    if (mRef.WasBufferPurged()) {
+      mFrame = nullptr;
+      mRef = nullptr;
+    }
+  }
+
+  DrawableFrameRef(DrawableFrameRef&& aOther)
+    : mFrame(aOther.mFrame.forget())
+    , mRef(Move(aOther.mRef))
   { }
 
-    ~AutoFrameLocker()
+  DrawableFrameRef& operator=(DrawableFrameRef&& aOther)
   {
-      if (mSucceeded) {
+    MOZ_ASSERT(this != &aOther, "Self-moves are prohibited");
+    mFrame = aOther.mFrame.forget();
+    mRef = Move(aOther.mRef);
+    return *this;
+  }
+
+  operator ConvertibleToBool() const
+  {
+    return bool(mFrame) ? &DrawableFrameRef::nonNull : 0;
+  }
+
+  imgFrame* operator->()
+  {
+    MOZ_ASSERT(mFrame);
+    return mFrame;
+  }
+
+  const imgFrame* operator->() const
+  {
+    MOZ_ASSERT(mFrame);
+    return mFrame;
+  }
+
+  imgFrame* get() { return mFrame; }
+  const imgFrame* get() const { return mFrame; }
+
+  void reset()
+  {
+    mFrame = nullptr;
+    mRef = nullptr;
+  }
+
+private:
+  nsRefPtr<imgFrame> mFrame;
+  VolatileBufferPtr<uint8_t> mRef;
+};
+
+/**
+ * A reference to an imgFrame that holds the imgFrame's surface in memory in a
+ * format appropriate for access as raw data. If you have a RawAccessFrameRef
+ * |ref| and |if (ref)| is true, then calls to GetImageData(), GetPaletteData(),
+ * and GetDrawTarget() are guaranteed to succeed. This guarantee is stronger
+ * than DrawableFrameRef, so everything that a valid DrawableFrameRef guarantees
+ * is also guaranteed by a valid RawAccessFrameRef.
+ *
+ * This may be considerably more expensive than is necessary just for drawing,
+ * so only use this when you need to read or write the raw underlying image data
+ * that the imgFrame holds.
+ */
+class RawAccessFrameRef MOZ_FINAL
+{
+  // Implementation details for safe boolean conversion.
+  typedef void (RawAccessFrameRef::* ConvertibleToBool)(float*****, double*****);
+  void nonNull(float*****, double*****) {}
+
+public:
+  RawAccessFrameRef() { }
+
+  explicit RawAccessFrameRef(imgFrame* aFrame)
+    : mFrame(aFrame)
+  {
+    MOZ_ASSERT(mFrame, "Need a frame");
+
+    if (NS_FAILED(mFrame->LockImageData())) {
+      mFrame->UnlockImageData();
+      mFrame = nullptr;
+    }
+  }
+
+  RawAccessFrameRef(RawAccessFrameRef&& aOther)
+    : mFrame(aOther.mFrame.forget())
+  { }
+
+  ~RawAccessFrameRef()
+  {
+    if (mFrame) {
       mFrame->UnlockImageData();
     }
   }
 
-    // Whether the lock request succeeded.
-    bool Succeeded() { return mSucceeded; }
+  RawAccessFrameRef& operator=(RawAccessFrameRef&& aOther)
+  {
+    MOZ_ASSERT(this != &aOther, "Self-moves are prohibited");
+
+    if (mFrame) {
+      mFrame->UnlockImageData();
+    }
+
+    mFrame = aOther.mFrame.forget();
+
+    return *this;
+  }
+
+  operator ConvertibleToBool() const
+  {
+    return bool(mFrame) ? &RawAccessFrameRef::nonNull : 0;
+  }
+
+  imgFrame* operator->()
+  {
+    MOZ_ASSERT(mFrame);
+    return mFrame.get();
+  }
+
+  const imgFrame* operator->() const
+  {
+    MOZ_ASSERT(mFrame);
+    return mFrame;
+  }
+
+  imgFrame* get() { return mFrame; }
+  const imgFrame* get() const { return mFrame; }
+
+  void reset()
+  {
+    if (mFrame) {
+      mFrame->UnlockImageData();
+    }
+    mFrame = nullptr;
+  }
 
 private:
   nsRefPtr<imgFrame> mFrame;
-    bool mSucceeded;
 };
 
 } // namespace image