cc: Fix low-res impl-side painting artifacts

cc/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/picture_layer_impl.h"
 
 #include "base/time.h"
 #include "cc/append_quads_data.h"
 #include "cc/checkerboard_draw_quad.h"
 #include "cc/debug_border_draw_quad.h"
@@ skipping 151 matching lines @@
 void PictureLayerImpl::calculateContentsScale(
     float ideal_contents_scale,
     float* contents_scale_x,
     float* contents_scale_y,
     gfx::Size* content_bounds) {
   if (!drawsContent()) {
     DCHECK(!tilings_.num_tilings());
     return;
   }
 
+  float min_contents_scale = layerTreeImpl()->settings().minimumContentsScale;
+  ideal_contents_scale = std::max(ideal_contents_scale, min_contents_scale);
+
   ManageTilings(ideal_contents_scale);
 
   // The content scale and bounds for a PictureLayerImpl is somewhat fictitious.
   // There are (usually) several tilings at different scales.  However, the
   // content bounds is the (integer!) space in which quads are generated.
   // In order to guarantee that we can fill this integer space with any set of
   // tilings (and then map back to floating point texture coordinates), the
   // contents scale must be at least as large as the largest of the tilings.
-  float max_contents_scale = 1.f;
+  float max_contents_scale = min_contents_scale;

[danakj, 2013/01/07 20:24:02]

ah, i see, cool

   for (size_t i = 0; i < tilings_.num_tilings(); ++i) {
     const PictureLayerTiling* tiling = tilings_.tiling_at(i);
     max_contents_scale = std::max(max_contents_scale, tiling->contents_scale());
   }
 
   *contents_scale_x = max_contents_scale;
   *contents_scale_y = max_contents_scale;
   *content_bounds = gfx::ToCeiledSize(
       gfx::ScaleSize(bounds(), max_contents_scale, max_contents_scale));
 }
@@ skipping 53 matching lines @@
       return 0;
     // Masks only supported if they fit on exactly one tile.
     if (iter.geometry_rect() != content_rect)
       return 0;
     return iter->GetResourceId();
   }
   return 0;
 }
 
 void PictureLayerImpl::AddTiling(float contents_scale, gfx::Size tile_size) {
+  if (contents_scale < layerTreeImpl()->settings().minimumContentsScale)

[danakj, 2013/01/07 20:24:02]

should this be a dcheck? (having trouble seeing who calls this from grep..)

+    return;
+
   const PictureLayerTiling* tiling = tilings_.AddTiling(
       contents_scale,
       tile_size);
 
   // If a new tiling is created on the active tree, sync it to the pending tree
   // so that it can share the same tiles.
   if (layerTreeImpl()->IsPendingTree())
     return;
 
   PictureLayerImpl* pending_twin = static_cast<PictureLayerImpl*>(
@@ skipping 23 matching lines @@
       AddTiling(ideal_contents_scale, TileSize());
       // TODO(enne): Add a low-res tiling as well.
     }
   } else {
     // TODO(enne): This should be unnecessary once there are two trees.
     tilings_.Reset();
   }
 }
 
 }  // namespace cc