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

Source/core/html/canvas/CanvasRenderingContext2D.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  * Copyright (C) 2012 Intel Corporation. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
@@ skipping 1242 matching lines @@
     FloatRect dstRect(dx, dy, dw, dh);
 
     if (!std::isfinite(dstRect.x()) || !std::isfinite(dstRect.y()) || !std::isfinite(dstRect.width()) || !std::isfinite(dstRect.height())
         || !std::isfinite(srcRect.x()) || !std::isfinite(srcRect.y()) || !std::isfinite(srcRect.width()) || !std::isfinite(srcRect.height()))
         return;
 
     if (!dstRect.width() || !dstRect.height())
         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()) {
         ec = IndexSizeError;
         return;
     }
     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)
 {
     if (!image) {
         ec = TypeMismatchError;
         return;
     }
     LayoutSize s = size(image);
     drawImage(image, x, y, s.width(), s.height(), ec);
@@ skipping 1010 matching lines @@
 }
 
 PassRefPtr<Canvas2DContextAttributes> CanvasRenderingContext2D::getContextAttributes() const
 {
     RefPtr<Canvas2DContextAttributes> attributes = Canvas2DContextAttributes::create();
     attributes->setAlpha(m_hasAlpha);
     return attributes.release();
 }
 
 } // namespace WebCore