cc: Use medium filter quality for downscales.

cc/tiles/software_image_decode_controller.cc

 // Copyright 2015 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/tiles/software_image_decode_controller.h"
 
 #include <inttypes.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 816 matching lines @@
           << line;
     }
   }
   DCHECK_GE(budget.AvailableMemoryBytes(),
             locked_images_budget_.AvailableMemoryBytes())
       << line;
 #endif  // DCHECK_IS_ON()
 }
 
 // SoftwareImageDecodeControllerKey
 ImageDecodeControllerKey ImageDecodeControllerKey::FromDrawImage(

[chrishtr, 2016/09/22 21:30:27]

unittest this method

[vmpstr, 2016/09/22 21:38:41]

Good idea. Done.

     const DrawImage& image) {
   const SkSize& scale = image.scale();
   // If the src_rect falls outside of the image, we need to clip it since
   // otherwise we might end up with uninitialized memory in the decode process.
   // Note that the scale is still unchanged and the target size is now a
   // function of the new src_rect.
   gfx::Rect src_rect = gfx::IntersectRects(
       gfx::SkIRectToRect(image.src_rect()),
       gfx::Rect(image.image()->width(), image.image()->height()));
 
   gfx::Size target_size(
       SkScalarRoundToInt(std::abs(src_rect.width() * scale.width())),
       SkScalarRoundToInt(std::abs(src_rect.height() * scale.height())));
 
   // Start with the quality that was requested.
   SkFilterQuality quality = image.filter_quality();
 
   // If we're not going to do a scale, we can use low filter quality. Note that
   // checking if the sizes are the same is better than checking if scale is 1.f,
   // because even non-1 scale can result in the same (rounded) width/height.
+  // If either dimension is a downscale, then use mipmaps (medium filter
+  // quality).
   if (target_size.width() == src_rect.width() &&
       target_size.height() == src_rect.height()) {
     quality = std::min(quality, kLow_SkFilterQuality);
+  } else if (target_size.width() < src_rect.width() ||
+             target_size.height() < src_rect.height()) {
+    quality = std::min(quality, kMedium_SkFilterQuality);
   }
 
   // Drop from high to medium if the the matrix we applied wasn't decomposable,
   // or if the scaled image will be too large.
   if (quality == kHigh_SkFilterQuality) {
     if (!image.matrix_is_decomposable()) {
       quality = kMedium_SkFilterQuality;
     } else {
       base::CheckedNumeric<size_t> size = 4u;
       size *= target_size.width();
@@ skipping 226 matching lines @@
       // TODO(tasak): free this component's caches as much as possible before
       // suspending renderer.
       break;
     case base::MemoryState::UNKNOWN:
       // NOT_REACHED.
       break;
   }
 }
 
 }  // namespace cc