Add support for PNG representation in gfx::Image

ui/gfx/image/image_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 "ui/gfx/image/image.h"
+
+#import <AppKit/AppKit.h>
+
+#include "base/logging.h"
+#include "base/memory/scoped_nsobject.h"
+
+namespace gfx {
+namespace internal {
+
+void PNGFromNSImage(NSImage* nsimage, std::vector<unsigned char>* png) {
+    CGImageRef cgimage = [nsimage CGImageForProposedRect:NULL

[Robert Sesek, 2012/07/24 18:59:17]

These functions should only be indented 2 spaces. Also, the convention in an
ObjC method call is to align the ':' vertically.

[Robert Sesek, 2012/07/24 18:59:17]

Why do you need to go through CGImage? Can you not just use +[NSBitmapImageRep
representationOfImageRepsInArray:usingType:properties:]?

[cjhopman, 2012/07/25 21:13:29]

Done.

[cjhopman, 2012/07/25 21:13:29]

I really don't know about this stuff, so here's some links where I got my
information:
http://cocoadev.com/wiki/NSImageToJPEG
http://cocoadev.com/wiki/NSBitmapImageRep

From these (and some cocoa-dev ml posts) it seems that
representationOfImageRepsInArray requires that the NSImage have an
NSBitmapImageRep which is not always the case. Going through a CGImage with
CGImageForProposedRect is suggested as a performant way of getting a
NSBitmapImageRep from an NSImage.

[Robert Sesek, 2012/07/31 14:07:16]

Thanks for the links. This looks right, then.

+                          context:nil
+                          hints:nil];
+    scoped_nsobject<NSBitmapImageRep> nsbitmap(

[Robert Sesek, 2012/07/24 18:59:17]

naming: ns_bitmap and cg_image

[cjhopman, 2012/07/25 21:13:29]

Done.

+        [[NSBitmapImageRep alloc] initWithCGImage:cgimage]);
+    NSData* nsdata = [nsbitmap representationUsingType:NSPNGFileType
+                      properties:nil];
+    const unsigned char* bytes =
+        static_cast<const unsigned char*>([nsdata bytes]);
+    png->assign(bytes, bytes + [nsdata length]);
+}
+
+NSImage* NSImageFromPNG(const std::vector<unsigned char>& png) {
+    scoped_nsobject<NSData> nsdata(
+        [[NSData alloc] initWithBytes:&png.front()
+        length:png.size()]);
+    scoped_nsobject<NSImage> image([[NSImage alloc] initWithData:nsdata]);
+    if (!image) {
+      LOG(WARNING) << "Unable to decode PNG, returning empty bitmap.";
+      image.reset([[NSImage alloc] initWithSize:NSMakeSize(1, 1)]);
+    }
+    return image.release();
+}
+
+} // namespace internal
+} // namespace gfx
+