Set CG clip to empty explicitly

skia/ext/skia_utils_mac.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "skia/ext/skia_utils_mac.h"
 
 #import <AppKit/AppKit.h>
 
 #include "base/logging.h"
 #include "base/mac/mac_util.h"
@@ skipping 315 matching lines @@
     kCGBitmapByteOrder32Host | kCGImageAlphaPremultipliedFirst);
 
   // Apply device matrix.
   CGAffineTransform contentsTransform = CGAffineTransformMakeScale(1, -1);
   contentsTransform = CGAffineTransformTranslate(contentsTransform, 0,
       -device->height());
   CGContextConcatCTM(cgContext_, contentsTransform);
 
   // Apply clip in device coordinates.
   CGMutablePathRef clipPath = CGPathCreateMutable();
-  SkRegion::Iterator iter(canvas_->getTotalClip());
+  const SkRegion& clipRgn = canvas_->getTotalClip();
+  if (clipRgn.isEmpty()) {
+    /* CoreGraphics does not consider a newly created path to be empty.

[Stephen White, 2012/01/31 19:44:45]

Nit:  the rest of this file uses // for multiline comments.

+       Explicitly set it to empty so the subsequent drawing is clipped out.
+       It would be better to make the CGContext hidden if there was a CG call
+       that does that.
+     */
+    CGPathAddRect(clipPath, 0, CGRectMake(0, 0, 0, 0));
+  }
+  SkRegion::Iterator iter(clipRgn);
   const SkIPoint& pt = device->getOrigin();
   for (; !iter.done(); iter.next()) {
     SkIRect skRect = iter.rect();
     skRect.offset(-pt);
     CGRect cgRect = SkIRectToCGRect(skRect);
     CGPathAddRect(clipPath, 0, cgRect);
   }
   CGContextAddPath(cgContext_, clipPath);
   CGContextClip(cgContext_);
   CGPathRelease(clipPath);
 
   // Apply content matrix.
   SkMatrix skMatrix = canvas_->getTotalMatrix();
   skMatrix.postTranslate(-SkIntToScalar(pt.fX), -SkIntToScalar(pt.fY));
   CGAffineTransform affine = SkMatrixToCGAffineTransform(skMatrix);
   CGContextConcatCTM(cgContext_, affine);
   
   return cgContext_;
 }
 
 }  // namespace gfx