Simplify platform_canvas.h by recognizing that PlatformCanvas does not actually extend

skia/ext/bitmap_platform_device_mac.cc

 // 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/bitmap_platform_device_mac.h"
 
 #import <ApplicationServices/ApplicationServices.h>
 #include <time.h>
 
 #include "base/mac/mac_util.h"
@@ skipping 10 matching lines @@
 
 namespace {
 
 static CGContextRef CGContextForData(void* data, int width, int height) {
 #define HAS_ARGB_SHIFTS(a, r, g, b) \
             (SK_A32_SHIFT == (a) && SK_R32_SHIFT == (r) \
              && SK_G32_SHIFT == (g) && SK_B32_SHIFT == (b))
 #if defined(SK_CPU_LENDIAN) && HAS_ARGB_SHIFTS(24, 16, 8, 0)
   // Allocate a bitmap context with 4 components per pixel (BGRA).  Apple
   // recommends these flags for improved CG performance.
+
+  // CGBitmapContextCreate returns NULL if width/height are 0. However, our
+  // callers expect to get a canvas back (which they later resize/reallocate)
+  // so we pin the dimensions here.
+  width = SkMax32(1, width);
+  height = SkMax32(1, height);
   CGContextRef context =
       CGBitmapContextCreate(data, width, height, 8, width * 4,
                             base::mac::GetSystemColorSpace(),
                             kCGImageAlphaPremultipliedFirst |
                                 kCGBitmapByteOrder32Host);
 #else
 #error We require that Skia's and CoreGraphics's recommended \
        image memory layout match.
 #endif
 #undef HAS_ARGB_SHIFTS
@@ skipping 207 matching lines @@
 
 SkDevice* BitmapPlatformDevice::onCreateCompatibleDevice(
     SkBitmap::Config config, int width, int height, bool isOpaque,
     Usage /*usage*/) {
   SkASSERT(config == SkBitmap::kARGB_8888_Config);
   SkDevice* bitmap_device = BitmapPlatformDevice::CreateAndClear(width, height,
                                                                  isOpaque);
   return bitmap_device;
 }
 
+// PlatformCanvas impl
+
+SkCanvas* CreatePlatformCanvas(CGContextRef ctx, int width, int height,
+                               bool is_opaque, OnFailureType failureType) {
+  SkDevice* dev = BitmapPlatformDevice::Create(ctx, width, height, is_opaque);
+  return CreateCanvas(dev, failureType);
+}
+
+SkCanvas* CreatePlatformCanvas(int width, int height, bool is_opaque,
+                               uint8_t* data, OnFailureType failureType) {
+  SkDevice* dev = BitmapPlatformDevice::CreateWithData(data, width, height,
+                                                       is_opaque);
+  return CreateCanvas(dev, failureType);
+}
+
 // Port of PlatformBitmap to mac
 
 PlatformBitmap::~PlatformBitmap() {
   if (surface_)
     CGContextRelease(surface_);
 }
 
 bool PlatformBitmap::Allocate(int width, int height, bool is_opaque) {
   if (RasterDeviceTooBigToAllocate(width, height))
     return false;
     
   bitmap_.setConfig(SkBitmap::kARGB_8888_Config, width, height, width * 4);
   if (!bitmap_.allocPixels())
       return false;
 
   if (!is_opaque)
     bitmap_.eraseColor(0);
   bitmap_.setIsOpaque(is_opaque);
 
   surface_ = CGContextForData(bitmap_.getPixels(), bitmap_.width(),
                               bitmap_.height());
   return true;
 }
 
 }  // namespace skia