cc: Do not create separate tilings for almost equal scale factors.

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 <algorithm>
 #include <cmath>
 #include <limits>
 #include <set>
@@ skipping 30 matching lines @@
 
 // Even for really wide viewports, at some point GPU raster should use
 // less than 4 tiles to fill the viewport. This is set to 256 as a
 // sane minimum for now, but we might want to tune this for low-end.
 const int kMinHeightForGpuRasteredTile = 256;
 
 // When making odd-sized tiles, round them up to increase the chances
 // of using the same tile size.
 const int kTileRoundUp = 64;
 
+// The precision value for rounding floating points values of scale factors.
+// With this scale factors will be having 3 digits fractional part, which will
+// make almost equal (having smaller difference by some magnitude of floating
+// point epsilon) scale factors to be considered as same.
+const int kScalePrecision = 4;
+
 }  // namespace
 
 namespace cc {
 
 PictureLayerImpl::PictureLayerImpl(
     LayerTreeImpl* tree_impl,
     int id,
     bool is_mask,
     scoped_refptr<SyncedScrollOffset> scroll_offset)
     : LayerImpl(tree_impl, id, scroll_offset),
@@ skipping 874 matching lines @@
 }
 
 void PictureLayerImpl::RecalculateRasterScales() {
   float old_raster_contents_scale = raster_contents_scale_;
   float old_raster_page_scale = raster_page_scale_;
   float old_raster_source_scale = raster_source_scale_;
 
   raster_device_scale_ = ideal_device_scale_;
   raster_page_scale_ = ideal_page_scale_;
   raster_source_scale_ = ideal_source_scale_;
-  raster_contents_scale_ = ideal_contents_scale_;
+  // Get fixed precision scale to avoid creating extra tilings for scales
+  // which are almost equal.
+  raster_contents_scale_ =
+      MathUtil::RoundToFixedPrecision(ideal_contents_scale_, kScalePrecision);
 
   // If we're not animating, or leaving an animation, and the
   // ideal_source_scale_ changes, then things are unpredictable, and we fix
   // the raster_source_scale_ in place.
   if (old_raster_source_scale &&
       !draw_properties().screen_space_transform_is_animating &&
       !was_screen_space_transform_animating_ &&
       old_raster_source_scale != ideal_source_scale_)
     raster_source_scale_is_fixed_ = true;
 
@@ skipping 307 matching lines @@
 
 bool PictureLayerImpl::IsOnActiveOrPendingTree() const {
   return !layer_tree_impl()->IsRecycleTree();
 }
 
 bool PictureLayerImpl::HasValidTilePriorities() const {
   return IsOnActiveOrPendingTree() && IsDrawnRenderSurfaceLayerListMember();
 }
 
 }  // namespace cc