cc: Stretch textures by .5 texels to prevent out of bounds sampling

cc/picture_layer_tiling.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_tiling.h"
 
 #include "base/debug/trace_event.h"
 #include "cc/math_util.h"
 #include "ui/gfx/point_conversions.h"
 #include "ui/gfx/rect_conversions.h"
@@ skipping 115 matching lines @@
 
   for (Region::Iterator region_iter(layer_invalidation);
        region_iter.has_rect();
        region_iter.next()) {
 
     gfx::Rect layer_invalidation = region_iter.rect();
     layer_invalidation.Intersect(gfx::Rect(layer_bounds_));
     gfx::Rect rect =
         gfx::ToEnclosingRect(ScaleRect(layer_invalidation, contents_scale_));
 
-    for (PictureLayerTiling::Iterator tile_iter(this, contents_scale_, rect);
+    for (PictureLayerTiling::Iterator tile_iter(this, contents_scale_, rect,
+                                                PictureLayerTiling::LayerDeviceAlignmentUnknown);
          tile_iter;
          ++tile_iter) {
       TileMapKey key(tile_iter.tile_i_, tile_iter.tile_j_);
       TileMap::iterator found = tiles_.find(key);
       if (found == tiles_.end())
         continue;
 
       tiles_.erase(found);
       new_tiles.push_back(key);
     }
@@ skipping 26 matching lines @@
       tile_i_(0),
       tile_j_(0),
       left_(0),
       top_(0),
       right_(-1),
       bottom_(-1) {
 }
 
 PictureLayerTiling::Iterator::Iterator(const PictureLayerTiling* tiling,
                                        float dest_scale,
-                                       gfx::Rect dest_rect)
+                                       gfx::Rect dest_rect,
+                                       LayerDeviceAlignment layerDeviceAlignment)
     : tiling_(tiling),
       dest_rect_(dest_rect),
       current_tile_(NULL),
       dest_to_content_scale_x_(0),
       dest_to_content_scale_y_(0),
       tile_i_(0),
       tile_j_(0),
       left_(0),
       top_(0),
       right_(-1),
@@ skipping 12 matching lines @@
   // The last row/column of texels may not have full rasterization coverage,
   // which can happen if the ceiled content size does not equal the floored
   // content size.  These texels will sample outside of the recording to
   // generate their pixels.  Use the floored size here to ignore them.
   gfx::Size content_size_floor = gfx::ToFlooredSize(tiling->ContentSizeF());
   dest_to_content_scale_x_ = content_size_floor.width() /
       static_cast<float>(dest_content_size.width());
   dest_to_content_scale_y_ = content_size_floor.height() /
       static_cast<float>(dest_content_size.height());
 
+  // It's possible that when drawing a quad with texel:pixel ratio < 1
+  // GL_LINEAR will cause us to blend in invalid texels.
+  // We stretch the content a little more to prevent sampling past the
+  // middle of the last texel.
+  if (layerDeviceAlignment == LayerAlignedToDevice){

[brianderson, 2013/02/13 00:10:19]

This is where the scale is taken into account.

Although we use GL_LINEAR when dest_to_content_scale > 1, we don't risk sampling
outside of texels bounds when texel:pixel ration > 1.

+    if (dest_to_content_scale_x_ < 1.0)
+      dest_to_content_scale_x_ -= 0.5f / dest_content_size.width();
+    if (dest_to_content_scale_y_ < 1.0)
+      dest_to_content_scale_y_ -= 0.5f / dest_content_size.height();
+  }
+  else if (layerDeviceAlignment == LayerNotAlignedToDevice) {
+    dest_to_content_scale_x_ -= 0.5f / dest_content_size.width();
+    dest_to_content_scale_y_ -= 0.5f / dest_content_size.height();
+  }
+
   gfx::Rect content_rect =
       gfx::ToEnclosingRect(gfx::ScaleRect(dest_rect_,
                                           dest_to_content_scale_x_,
                                           dest_to_content_scale_y_));
   // IndexFromSrcCoord clamps to valid tile ranges, so it's necessary to
   // check for non-intersection first.
   content_rect.Intersect(gfx::Rect(tiling_->tiling_data_.total_size()));
   if (content_rect.IsEmpty())
     return;
 
@@ skipping 272 matching lines @@
     // and recreated, then that picture pile ref could exist indefinitely.  To
     // prevent this, ask the client to update the pile to its own ref.  This
     // will cause PicturePileImpls and their clones to get deleted once the
     // corresponding PictureLayerImpl and any in flight raster jobs go out of
     // scope.
     client_->UpdatePile(it->second);
   }
 }
 
 }  // namespace cc