Fullscreen tab capture: Prefer standard resolutions

content/browser/media/capture/web_contents_video_capture_device.cc

Index: content/browser/media/capture/web_contents_video_capture_device.cc
diff --git a/content/browser/media/capture/web_contents_video_capture_device.cc b/content/browser/media/capture/web_contents_video_capture_device.cc
index d90cbd1891668dfa502b55118a22060e5cd0bc80..2eaea1155ed705f6c33a071f87872df5a10f3f7e 100644
--- a/content/browser/media/capture/web_contents_video_capture_device.cc
+++ b/content/browser/media/capture/web_contents_video_capture_device.cc
@@ -642,6 +642,30 @@ gfx::Size WebContentsCaptureMachine::ComputeOptimalViewSize() const {
   // http://crbug.com/350491
   gfx::Size optimal_size = oracle_proxy_->max_frame_size();
 
+  // If the max frame size is close to a common video aspect ratio, compute a
+  // standard resolution for that aspect ratio.  For example, given 1365x768,
+  // which is very close to 16:9, the optimal size would be 1280x720.  The
+  // purpose of this logic is to prevent scaling quality issues caused by "one
+  // pixel stretching" and/or odd-to-even dimension scaling, and to improve the
+  // performance of consumers of the captured video.
+  const auto HasIntendedAspectRatio = [](const gfx::Size& size, int x, int y) {

[Kevin M, 2015/07/30 00:23:06]

Can you factor this out into a standalone fn that takes gfx::Size and write some
unit tests for it?

[miu, 2015/07/30 20:22:53]

Done.  Didn't factor anything out, but did write unit tests.

+    const int a = y * size.width();
+    const int b = x * size.height();
+    const int percentage_diff = 100 * std::abs((a - b)) / b;
+    return percentage_diff <= 1;  // Effectively, anything strictly <2%.
+  };
+  const auto RoundToExactAspectRatio = [](const gfx::Size& size, int x, int y) {
+    const int adjusted_height =

[Kevin M, 2015/07/30 00:23:06]

Can you add some comments or pick a more descriptive name for x & y to
communicate the requirements for even multiples?

[miu, 2015/07/30 20:22:53]

Done.

+        std::max(size.height() - (size.height() % y), y);
+    DCHECK_EQ((adjusted_height * x) % y, 0);
+    return gfx::Size(adjusted_height * x / y, adjusted_height);
+  };
+  if (HasIntendedAspectRatio(optimal_size, 16, 9))
+    optimal_size = RoundToExactAspectRatio(optimal_size, 160, 90);
+  else if (HasIntendedAspectRatio(optimal_size, 4, 3))
+    optimal_size = RoundToExactAspectRatio(optimal_size, 64, 48);
+  // Else, do not make an adjustment.
+
   // If the ratio between physical and logical pixels is greater than 1:1,
   // shrink |optimal_size| by that amount.  Then, when external code resizes the
   // render widget to the "preferred size," the widget will be physically