Properly flip the CGContext during UIImage->SkBitmap conversions.

skia/ext/skia_utils_ios.mm

 // Copyright 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_ios.h"
 
 #import <UIKit/UIKit.h>
 
 #include "base/logging.h"
 #include "base/mac/scoped_cftyperef.h"
@@ skipping 29 matching lines @@
 #else
 #error We require that Skia's and CoreGraphics's recommended \
        image memory layout match.
 #endif
 #undef HAS_ARGB_SHIFTS
 
   DCHECK(context);
   if (!context)
     return bitmap;
 
+  // We need to invert the y-axis of the canvas so that Core Graphics drawing
+  // happens right-side up. Skia has an upper-left origin and CG has a lower-
+  // left one.
+  CGContextScaleCTM(context, 1.0, -1.0);
+  CGContextTranslateCTM(context, 0, -size.height);
+
   // UIGraphicsPushContext be called from the main thread.
   // TODO(rohitrao): We can use CG to make this thread safe, but the mac code
   // calls setCurrentContext, so it's similarly limited to the main thread.
   DCHECK([NSThread isMainThread]);
   UIGraphicsPushContext(context);
   [image drawInRect:CGRectMake(0, 0, size.width, size.height)
           blendMode:kCGBlendModeCopy
               alpha:1.0];
   UIGraphicsPopContext();
 
   return bitmap;
 }
 
 UIImage* SkBitmapToUIImageWithColorSpace(const SkBitmap& skia_bitmap,
                                          CGColorSpaceRef color_space) {
   if (skia_bitmap.isNull())
     return nil;
 
   // First convert SkBitmap to CGImageRef.
   base::mac::ScopedCFTypeRef<CGImageRef> cg_image(
       SkCreateCGImageRefWithColorspace(skia_bitmap, color_space));
 
   // Now convert to UIImage.
   // TODO(rohitrao): Gotta incorporate the scale factor somewhere!
   return [UIImage imageWithCGImage:cg_image.get()];
 }
 
 }  // namespace gfx