cc: Made image comparison for pixel tests error tolerant.

cc/test/pixel_test_utils.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 "cc/test/pixel_test_utils.h"
 
 #include "base/file_util.h"
 #include "base/logging.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "ui/gfx/codec/png_codec.h"
@@ skipping 16 matching lines @@
 
 bool ReadPNGFile(const base::FilePath& file_path, SkBitmap* bitmap) {
   DCHECK(bitmap);
   std::string png_data;
   return file_util::ReadFileToString(file_path, &png_data) &&
          gfx::PNGCodec::Decode(reinterpret_cast<unsigned char*>(&png_data[0]),
                                png_data.length(),
                                bitmap);
 }
 
-bool IsSameAsPNGFile(const SkBitmap& gen_bmp, base::FilePath ref_img_path) {
+bool MatchesPNGFile(const SkBitmap& gen_bmp, base::FilePath ref_img_path,
+                    const PixelComparator& comparator) {
   SkBitmap ref_bmp;
   if (!ReadPNGFile(ref_img_path, &ref_bmp)) {
     LOG(ERROR) << "Cannot read reference image: " << ref_img_path.value();
     return false;
   }
 
-  if (ref_bmp.width() != gen_bmp.width() ||
-      ref_bmp.height() != gen_bmp.height()) {
+  // Check if images size matches
+  if (gen_bmp.width() != ref_bmp.width() ||
+      gen_bmp.height() != ref_bmp.height()) {
     LOG(ERROR)
-        << "Dimensions do not match (Expected) vs (Actual):"
-        << "(" << ref_bmp.width() << "x" << ref_bmp.height()
-            << ") vs. "
-        << "(" << gen_bmp.width() << "x" << gen_bmp.height() << ")";
+        << "Dimensions do not match! "
+        << "Actual: " << gen_bmp.width() << "x" << gen_bmp.height()
+        << "; "
+        << "Expected: " << ref_bmp.width() << "x" << ref_bmp.height();

[reveman, 2013/03/08 04:41:57]

nit: I'd avoid changing this just to make the patch cleaner but if you think
this output is better that's fine too.

     return false;
   }
 
-  // Compare pixels and create a simple diff image.
-  int diff_pixels_count = 0;
-  SkAutoLockPixels lock_bmp(gen_bmp);
-  SkAutoLockPixels lock_ref_bmp(ref_bmp);
-  // The reference images were saved with no alpha channel. Use the mask to
-  // set alpha to 0.
-  uint32_t kAlphaMask = 0x00FFFFFF;

[reveman, 2013/03/08 04:41:57]

oh, sorry I didn't realize the old code was doing this. thanks for improving
this in this patch. I think as a follow up we might want to change the ref
images to contain alpha and include that in our comparison. 

-  for (int x = 0; x < gen_bmp.width(); ++x) {
-    for (int y = 0; y < gen_bmp.height(); ++y) {
-      if ((*gen_bmp.getAddr32(x, y) & kAlphaMask) !=
-          (*ref_bmp.getAddr32(x, y) & kAlphaMask)) {
-        ++diff_pixels_count;
-      }
-    }
-  }
+  // Shortcut for empty images. They are always equal.
+  if (gen_bmp.width() == 0 || gen_bmp.height() == 0)
+    return true;
 
-  if (diff_pixels_count != 0) {
-    LOG(ERROR) << "Images differ by pixel count: " << diff_pixels_count;
-    return false;
-  }
-
-  return true;
+  return comparator.Compare(gen_bmp, ref_bmp);
 }
 
 }  // namespace cc