Use SkImage as a backing store for copying 2d Contexts to ImageBitmaps.

Source/core/html/canvas/CanvasRenderingContext2D.cpp

Index: Source/core/html/canvas/CanvasRenderingContext2D.cpp
diff --git a/Source/core/html/canvas/CanvasRenderingContext2D.cpp b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
index b2701331d1dffccff104b5be49378965be011792..fad7774e4d43df7dd25f693e5d45a23e24f3f594 100644
--- a/Source/core/html/canvas/CanvasRenderingContext2D.cpp
+++ b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
@@ -1260,12 +1260,8 @@ void CanvasRenderingContext2D::drawImage(ImageBitmap* bitmap,
         return;
 
     ASSERT(bitmap->height() && bitmap->width());
-
     FloatRect normalizedSrcRect = normalizeRect(srcRect);
     FloatRect normalizedDstRect = normalizeRect(dstRect);
-    FloatRect actualDstRect(FloatPoint(bitmap->bitmapOffset()), bitmap->bitmapSize());
-    actualDstRect.scale(normalizedDstRect.width() / bitmap->width(), normalizedDstRect.height() / bitmap->height());

[Justin Novosad, 2013/07/22 15:35:41]

This is not correct. What you should be doing here is offset and clamp the
source rect.  There should not be any scaling.  Actually6, I have a CL in flight
that fixes a bug with source rect clamping here.  We should land that first so
you can re-use that code to do the right thing here.

-    actualDstRect.moveBy(normalizedDstRect.location());
 
     FloatRect imageRect = FloatRect(FloatPoint(), bitmap->bitmapSize());
     if (!srcRect.width() || !srcRect.height()) {
@@ -1275,9 +1271,18 @@ void CanvasRenderingContext2D::drawImage(ImageBitmap* bitmap,
     if (!imageRect.contains(normalizedSrcRect))
         return;
 
-    Image* imageForRendering = bitmap->bitmapImage();
-
-    drawImageInternal(imageForRendering, normalizedSrcRect, actualDstRect, state().m_globalComposite, state().m_globalBlend);
+    Image* imageForRendering = bitmap->bitmapImage().get();
+    if (bitmap->derivedFromCanvas()) {
+        FloatRect originalCropRect(bitmap->cropRect());
+        normalizedSrcRect.moveBy(originalCropRect.location());
+        FloatRect actualSrcRect = intersection(originalCropRect, normalizedSrcRect);
+        drawImageInternal(imageForRendering, actualSrcRect, normalizedDstRect, state().m_globalComposite, state().m_globalBlend);
+    } else {
+        FloatRect actualDstRect(FloatPoint(bitmap->bitmapOffset()), bitmap->bitmapSize());
+        actualDstRect.scale(normalizedDstRect.width() / bitmap->width(), normalizedDstRect.height() / bitmap->height());
+        actualDstRect.moveBy(normalizedDstRect.location());
+        drawImageInternal(imageForRendering, normalizedSrcRect, actualDstRect, state().m_globalComposite, state().m_globalBlend);
+    }
 }
 
 void CanvasRenderingContext2D::drawImage(HTMLImageElement* image, float x, float y, ExceptionCode& ec)