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 ImageComparator& 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()) {
     LOG(ERROR)
         << "Dimensions do not match (Expected) vs (Actual):"
         << "(" << ref_bmp.width() << "x" << ref_bmp.height()
             << ") vs. "
         << "(" << gen_bmp.width() << "x" << gen_bmp.height() << ")";
     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;
-  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;
-      }
-    }
-  }
+  ImageComparator::ErrorMetrics metrics;
+  if (!comparator.Compare(gen_bmp, ref_bmp, &metrics)) {

[reveman, 2013/03/07 07:50:44]

could the comparator instead be responsible for printing an error message?

[ernstm, 2013/03/07 19:30:07]

Done.

+    LOG(ERROR) << "Percentage of pixels that are different: "
+               << metrics.error_pixels_percentage << "; "
+               << "Percentage of pixels with errors not greater than "
+               << metrics.small_error_threshold << ": "
+               << metrics.small_error_pixels_percentage << "; "
+               << "Average absolute error over different pixels: "
+               << "R=" << metrics.avg_abs_error_r << " "
+               << "G=" << metrics.avg_abs_error_g << " "
+               << "B=" << metrics.avg_abs_error_b << "; "
+               << "Maximum absolute error: "
+               << "R=" << metrics.max_abs_error_r << " "
+               << "G=" << metrics.max_abs_error_g << " "
+               << "B=" << metrics.max_abs_error_b;
 
-  if (diff_pixels_count != 0) {
-    LOG(ERROR) << "Images differ by pixel count: " << diff_pixels_count;
     return false;
   }
 
   return true;
 }
 
 }  // namespace cc