cc: Made image comparison for pixel tests error tolerant.

cc/test/pixel_comparator.h

+// Copyright (c) 2013 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.
+
+#ifndef CC_TEST_PIXEL_COMPARATOR_H_
+#define CC_TEST_PIXEL_COMPARATOR_H_
+
+#include "third_party/skia/include/core/SkBitmap.h"
+
+namespace cc {
+
+// Interface for pixel comparators.
+class PixelComparator {
+ public:
+  virtual bool Compare(const SkBitmap& actual_bmp,
+                       const SkBitmap& expected_bmp) const = 0;
+
+ protected:
+  virtual ~PixelComparator() {};

[reveman, 2013/03/07 21:41:25]

don't need a ; after a }

[ernstm, 2013/03/08 00:14:46]

Done.

+  // Returns true if the two bitmaps have the same dimensions. Otherwise returns
+  // false and outputs a message on LOG(ERROR)
+  bool CompareSize(const SkBitmap& actual_bmp,
+                   const SkBitmap& expected_bmp) const;

[reveman, 2013/03/07 21:41:25]

To keep this as clean as possible, I'd prefer to keep the size check in
IsSameAsPNGFile until someone implements a comparator that needs it. Also not
clear to me why we would ever allow the bitmaps to have different sizes.

[ernstm, 2013/03/08 00:14:46]

Done.

+};
+
+// Exact pixel comparator. Counts the number of pixel with an error.
+class ExactPixelComparator : public PixelComparator {
+ public:
+  // Returns true if the two bitmaps are identical. Otherwise, returns false
+  // and report the number of pixels with an error on LOG(ERROR).
+  bool Compare(const SkBitmap& actual_bmp, const SkBitmap& expected_bmp) const;
+};
+
+// Fuzzy pixel comparator. Counts small and arbitrary errors separately and
+// computes average and maximum absolute errors per color channel.
+class FuzzyPixelComparator : public PixelComparator {
+ public:
+  // Default values for constructor make comparator tolareate an arbitrary
+  // number of off-by-one errors.
+  FuzzyPixelComparator(const float error_pixels_percentage_limit = 100.0f,
+                       const float small_error_pixels_percentage_limit = 100.0f,
+                       const float avg_abs_error_limit = 1.0f,
+                       const unsigned int max_abs_error_limit = 1,
+                       const unsigned int small_error_threshold = 1);

[reveman, 2013/03/07 21:41:25]

Style guide doesn't allow default function parameters.

[ernstm, 2013/03/08 00:14:46]

Done.

+  // Computes error metrics and returns true if the errors don't exceed the
+  // specified limits. Otherwise, returns false and reports the error metrics on
+  // LOG(ERROR).
+  bool Compare(const SkBitmap& actual_bmp, const SkBitmap& expected_bmp) const;
+
+ private:
+  // Limit for percentage of pixels with an error
+  float error_pixels_percentage_limit_;
+  // Limit for percentage of pixels with a small error
+  float small_error_pixels_percentage_limit_;
+  // Limit for average absolute error (excluding identical pixels)
+  float avg_abs_error_limit_;
+  // Limit for largest absolute error
+  unsigned int max_abs_error_limit_;
+  // Threshold for small errors
+  unsigned int small_error_threshold_;
+};
+
+}  // namespace cc
+
+#endif  // CC_TEST_PIXEL_COMPARATOR_H_