[2/5] Disable transformed rasterization if layer is opaque

cc/layers/picture_layer_impl.cc

 // Copyright 2012 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/layers/picture_layer_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 644 matching lines @@
     AddDamageRect(layer_damage_rect);
   }
   if (tile->draw_info().NeedsRaster()) {
     PictureLayerTiling* tiling =
         tilings_->FindTilingWithScaleKey(tile->contents_scale_key());
     if (tiling)
       tiling->set_all_tiles_done(false);
   }
 }
 
+SimpleEnclosedRegion PictureLayerImpl::VisibleOpaqueRegion() const {
+  if (use_transformed_rasterization_)
+    return SimpleEnclosedRegion();

[enne (OOO), 2017/01/03 22:53:08]

Why not VisibleOpaqueRegion but Inset by 1?

[trchen, 2017/01/14 00:46:46]

Because it depends on the actual raster scale. For example, a layer of size (99,
99) with raster scale 0.25, its opaque region in raster space would be
EnclosedRect(ScaleRect(Rect(99,99), 0.25)) == Rect(24, 24). When mapped back to
the layer space, it's only (96, 96).

For non-transformed-rasterized layer it is fine because the edge pixel will be
filled with opaque background color.

+  return LayerImpl::VisibleOpaqueRegion();
+}
+
 void PictureLayerImpl::DidBeginTracing() {
   raster_source_->DidBeginTracing();
 }
 
 void PictureLayerImpl::ReleaseResources() {
   // Recreate tilings with new settings, since some of those might change when
   // we release resources.
   tilings_ = nullptr;
   ResetRasterScale();
 }
@@ skipping 677 matching lines @@
 bool PictureLayerImpl::IsOnActiveOrPendingTree() const {
   return !layer_tree_impl()->IsRecycleTree();
 }
 
 bool PictureLayerImpl::HasValidTilePriorities() const {
   return IsOnActiveOrPendingTree() &&
          is_drawn_render_surface_layer_list_member();
 }
 
 }  // namespace cc