cc: Made image comparison for pixel tests error tolerant.

cc/test/image_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_IMAGE_COMPARATOR_H_
+#define CC_TEST_IMAGE_COMPARATOR_H_
+
+#include "third_party/skia/include/core/SkBitmap.h"
+
+namespace cc {
+
+class ImageComparator {
+ public:
+
+ struct ErrorMetrics {
+    ErrorMetrics(float error_pixels_percentage = 0.0f,
+                 float small_error_pixels_percentage = 0.0f,
+                 float avg_abs_error_r = 0.0f,
+                 float avg_abs_error_g = 0.0f,
+                 float avg_abs_error_b = 0.0f,
+                 unsigned int max_abs_error_r = 0,
+                 unsigned int max_abs_error_g = 0,
+                 unsigned int max_abs_error_b = 0,
+                 unsigned int small_error_threshold = 1);
+    // Percentage of pixels that are different in any way.
+    float error_pixels_percentage;
+    // Percentage of pixels that are at most off by small_error_threshold
+    // in each color channel.
+    float small_error_pixels_percentage;
+    // The per channel average absolute error over all pixels that are different.
+    float avg_abs_error_r;
+    float avg_abs_error_g;
+    float avg_abs_error_b;
+    // The per channel maxiumum absolute error over all pixels that are different
+    // (average over all pixels is the same).
+    unsigned int max_abs_error_r;
+    unsigned int max_abs_error_g;
+    unsigned int max_abs_error_b;
+    // The threshold that was used to classify small vs. large errors.
+    // Small errors are less or equal to this value.
+    unsigned int small_error_threshold;
+  };
+
+  // Strict image comparator with zero thresholds.
+  ImageComparator();
+  // User defined comparator with given thresholds.
+  ImageComparator(const ErrorMetrics& thresholds);
+
+   // Configure the comparator to allow a given percentage of off-by-one pixel errors
+  void AllowOffByOneErrors(float off_by_one_pixels_percentage = 100.0f);
+
+  // Compare two bitmaps. Return true if they are equal within the given thresholds
+  bool Compare(const SkBitmap& a, const SkBitmap& b, ErrorMetrics* return_metrics = NULL) const;
+
+ private:
+  ErrorMetrics thresholds_;
+};
+
+}  // namespace cc
+
+#endif  // CC_TEST_IMAGE_COMPARATOR_H_