cc: Made image comparison for pixel tests error tolerant.

cc/test/pixel_comparator.cc

Index: cc/test/pixel_comparator.cc
diff --git a/cc/test/pixel_comparator.cc b/cc/test/pixel_comparator.cc
new file mode 100644
index 0000000000000000000000000000000000000000..efe048725dd7e958a2d2b99811310d5efc0f27d2
--- /dev/null
+++ b/cc/test/pixel_comparator.cc
@@ -0,0 +1,174 @@
+// 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.
+
+#include "cc/test/pixel_comparator.h"
+
+#include <algorithm>
+
+#include "base/logging.h"
+
+namespace cc {
+
+bool ExactPixelComparator::Compare(const SkBitmap& actual_bmp,
+                                   const SkBitmap& expected_bmp) const {
+  // Number of pixels with an error
+  int error_pixels_count = 0;
+
+  // Check that bitmaps have identical dimensions.
+  DCHECK(actual_bmp.width() == expected_bmp.width() &&
+         actual_bmp.height() == expected_bmp.height());
+
+  SkAutoLockPixels lock_actual_bmp(actual_bmp);
+  SkAutoLockPixels lock_expected_bmp(expected_bmp);
+
+  for (int x = 0; x < actual_bmp.width(); ++x) {
+    for (int y = 0; y < actual_bmp.height(); ++y) {
+      // Fetch color values. Set alpha to 0, because rhe reference images were
+      // saved with no alpha channel.
+      SkColor actual_color = actual_bmp.getColor(x, y);
+      SkColorSetA(actual_color, 0);
+      SkColor expected_color = expected_bmp.getColor(x, y);
+      SkColorSetA(expected_color, 0);
+
+      if (actual_color != expected_color) {
+        ++error_pixels_count;
+      }
+    }
+  }
+
+  if (error_pixels_count != 0) {
+    LOG(ERROR) << "Number of pixel with an error: " << error_pixels_count;
+    return false;
+  }
+
+  return true;
+}
+
+FuzzyPixelComparator::FuzzyPixelComparator(
+    const float error_pixels_percentage_limit,
+    const float small_error_pixels_percentage_limit,
+    const float avg_abs_error_limit,
+    const int max_abs_error_limit,
+    const int small_error_threshold)
+    : error_pixels_percentage_limit_(error_pixels_percentage_limit),
+      small_error_pixels_percentage_limit_(small_error_pixels_percentage_limit),
+      avg_abs_error_limit_(avg_abs_error_limit),
+      max_abs_error_limit_(max_abs_error_limit),
+      small_error_threshold_(small_error_threshold) {
+}
+
+bool FuzzyPixelComparator::Compare(const SkBitmap& actual_bmp,
+                                   const SkBitmap& expected_bmp) const {
+  // Number of pixels with an error
+  int error_pixels_count = 0;
+  // Number of pixels with a small error
+  int small_error_pixels_count = 0;
+  // The per channel sums of absolute errors over all pixels.
+  int64 sum_abs_error_r = 0;
+  int64 sum_abs_error_g = 0;
+  int64 sum_abs_error_b = 0;
+  // The per channel maximum absolute errors over all pixels.
+  int max_abs_error_r = 0;
+  int max_abs_error_g = 0;
+  int max_abs_error_b = 0;
+
+  // Check that bitmaps have identical dimensions.
+  DCHECK(actual_bmp.width() == expected_bmp.width() &&
+         actual_bmp.height() == expected_bmp.height());
+
+  // Check that bitmaps are not empty.
+  DCHECK(actual_bmp.width() > 0 && actual_bmp.height() > 0);
+
+  SkAutoLockPixels lock_actual_bmp(actual_bmp);
+  SkAutoLockPixels lock_expected_bmp(expected_bmp);
+
+  for (int x = 0; x < actual_bmp.width(); ++x) {
+    for (int y = 0; y < actual_bmp.height(); ++y) {
+      // Fetch color values. Set alpha to 0, because rhe reference images were
+      // saved with no alpha channel.
+      SkColor actual_color = actual_bmp.getColor(x, y);
+      SkColorSetA(actual_color, 0);
+      SkColor expected_color = expected_bmp.getColor(x, y);
+      SkColorSetA(expected_color, 0);
+
+      if (actual_color != expected_color) {
+        ++error_pixels_count;
+
+        // Compute per channel absolute errors
+        int abs_error_r =
+            std::max(SkColorGetR(actual_color), SkColorGetR(expected_color)) -

[slavi, 2013/03/08 19:49:04]

Why not

std::abs(SkColorGetR(actual_color) - SkColorGetR(expected_color))

?

[ernstm, 2013/03/18 20:19:39]

Done.

+            std::min(SkColorGetR(actual_color), SkColorGetR(expected_color));
+        int abs_error_g =
+            std::max(SkColorGetG(actual_color), SkColorGetG(expected_color)) -
+            std::min(SkColorGetG(actual_color), SkColorGetG(expected_color));
+        int abs_error_b =
+            std::max(SkColorGetB(actual_color), SkColorGetB(expected_color)) -
+            std::min(SkColorGetB(actual_color), SkColorGetB(expected_color));
+
+        // Increment small error counter if error is below threshold
+        if (abs_error_r <= small_error_threshold_ &&
+            abs_error_g <= small_error_threshold_ &&
+            abs_error_b <= small_error_threshold_)
+          ++small_error_pixels_count;
+
+        // Update per channel maximum absolute errors
+        if (abs_error_r > max_abs_error_r) max_abs_error_r = abs_error_r;

[slavi, 2013/03/08 19:49:04]

max_abs_error_r = std::max(max_abs_error_r, abs_error_r);

[ernstm, 2013/03/18 20:19:39]

Done.

+        if (abs_error_g > max_abs_error_g) max_abs_error_g = abs_error_g;
+        if (abs_error_b > max_abs_error_b) max_abs_error_b = abs_error_b;

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

nit: put max_abs_error_? = abs_error_?; statements on next line.

[ernstm, 2013/03/18 20:19:39]

Done.

+
+        // Update per channel absolute error sums
+        sum_abs_error_r += abs_error_r;
+        sum_abs_error_g += abs_error_g;
+        sum_abs_error_b += abs_error_b;
+      }
+    }
+  }
+
+  // Compute error metrics from collected data
+  int pixels_count = actual_bmp.width() * actual_bmp.height();
+  float error_pixels_percentage = 0.0f;
+  float small_error_pixels_percentage = 0.0f;
+  if (pixels_count > 0) {
+    error_pixels_percentage = static_cast<float>(error_pixels_count) /
+        pixels_count * 100.0f;
+    small_error_pixels_percentage =
+        static_cast<float>(small_error_pixels_count) / pixels_count * 100.0f;
+  }
+  float avg_abs_error_r = 0.0f;
+  float avg_abs_error_g = 0.0f;
+  float avg_abs_error_b = 0.0f;
+  if (error_pixels_count > 0) {
+    avg_abs_error_r = static_cast<float>(sum_abs_error_r) / error_pixels_count;
+    avg_abs_error_g = static_cast<float>(sum_abs_error_g) / error_pixels_count;
+    avg_abs_error_b = static_cast<float>(sum_abs_error_b) / error_pixels_count;
+  }
+
+  if (error_pixels_percentage > error_pixels_percentage_limit_ ||
+      small_error_pixels_percentage > small_error_pixels_percentage_limit_ ||
+      avg_abs_error_r > avg_abs_error_limit_ ||
+      avg_abs_error_g > avg_abs_error_limit_ ||
+      avg_abs_error_b > avg_abs_error_limit_ ||
+      max_abs_error_r > max_abs_error_limit_ ||
+      max_abs_error_g > max_abs_error_limit_ ||
+      max_abs_error_b > max_abs_error_limit_) {
+    LOG(ERROR) << "Percentage of pixels with an error: "
+               << error_pixels_percentage << "; "
+               << "Percentage of pixels with errors not greater than "
+               << small_error_threshold_ << ": "
+               << small_error_pixels_percentage << "; "
+               << "Average absolute error (excluding identical pixels): "
+               << "R=" << avg_abs_error_r << " "
+               << "G=" << avg_abs_error_g << " "
+               << "B=" << avg_abs_error_b << "; "
+               << "Largest absolute error: "
+               << "R=" << max_abs_error_r << " "
+               << "G=" << max_abs_error_g << " "
+               << "B=" << max_abs_error_b;
+    return false;
+  } else {
+    return true;
+  }
+}
+
+}  // namespace cc