[Experimental] Avoid HQ resampling of non-trivially transformed images

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 815 matching lines @@
              pending_image_tasks_.find(key) != pending_image_tasks_.end())
           << line;
     }
   }
   DCHECK_GE(budget.AvailableMemoryBytes(),
             locked_images_budget_.AvailableMemoryBytes())
       << line;
 #endif  // DCHECK_IS_ON()
 }
 
+namespace {

[vmpstr, 2016/09/23 18:45:39]

Move this to the top of the file please.

+
+bool shouldDrawHighQuality(const DrawImage& image,

[vmpstr, 2016/09/23 18:45:39]

ShouldDrawHighQuality

+                           const gfx::Size& target_size) {
+  // Drop from high to medium if the the matrix we applied wasn't decomposable,
+  // or if the scaled image will be too large.
+  if (!image.matrix_is_decomposable()) {

[vmpstr, 2016/09/23 18:45:39]

braces optional for one liners

+    return false;
+  }
+
+  base::CheckedNumeric<size_t> size = 4u;
+  size *= target_size.width();
+  size *= target_size.height();
+  if (size.ValueOrDefault(std::numeric_limits<size_t>::max()) >
+      kMaxHighQualityImageSizeBytes) {
+    return false;
+  }
+
+  // Filtering twice due to non-trivial transforms or subpixel phase produces
+  // results worse than kMedium or kLow.  Just steer clear.
+  if (!image.matrix().isScaleTranslate()) {

[vmpstr, 2016/09/23 18:45:39]

Can you reorder these checks so that the easy checks are earlier than heavy
checks (that is, size check should probably be last)

+    return false;
+  }
+
+  SkRect dest;
+  image.matrix().mapRectScaleTranslate(&dest, SkRect::Make(image.src_rect()));
+  const SkIRect idest = dest.round();
+  if (!SkScalarNearlyEqual(dest.left(), idest.left()) ||
+      !SkScalarNearlyEqual(dest.top(), idest.top()) ||
+      !SkScalarNearlyEqual(dest.right(), idest.right()) ||
+      !SkScalarNearlyEqual(dest.bottom(), idest.bottom())) {
+    return false;
+  }
+
+  return true;
+}

[vmpstr, 2016/09/23 18:45:39]

I wonder if we should just drop to medium for downscales. Or do you think this
would produce better results?

+
+}  // anonymous namespace
+
 // SoftwareImageDecodeControllerKey
 ImageDecodeControllerKey ImageDecodeControllerKey::FromDrawImage(
     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 (target_size.width() == src_rect.width() &&
       target_size.height() == src_rect.height()) {
     quality = std::min(quality, kLow_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();
-      size *= target_size.height();
-      if (size.ValueOrDefault(std::numeric_limits<size_t>::max()) >
-          kMaxHighQualityImageSizeBytes) {
-        quality = kMedium_SkFilterQuality;
-      }
-    }
+  if (quality == kHigh_SkFilterQuality &&
+      !shouldDrawHighQuality(image, target_size)) {
+    quality = kMedium_SkFilterQuality;
   }
 
   // Drop from medium to low if the matrix we applied wasn't decomposable or if
   // we're enlarging the image in both dimensions.
   if (quality == kMedium_SkFilterQuality) {
     if (!image.matrix_is_decomposable() ||
         (scale.width() >= 1.f && scale.height() >= 1.f)) {
       quality = kLow_SkFilterQuality;
     }
   }
@@ skipping 210 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