cc: Optimize decode scheduling for checker-images.

cc/tiles/picture_layer_tiling.cc

Index: cc/tiles/picture_layer_tiling.cc
diff --git a/cc/tiles/picture_layer_tiling.cc b/cc/tiles/picture_layer_tiling.cc
index 344cb32b6c04cc92ce00887c8862c30add532d73..2af7298aaa0314a200cf0308e81d5fe7a659bbb6 100644
--- a/cc/tiles/picture_layer_tiling.cc
+++ b/cc/tiles/picture_layer_tiling.cc
@@ -808,6 +808,39 @@ bool PictureLayerTiling::IsTileRequiredForDraw(const Tile* tile) const {
   return true;
 }
 
+bool PictureLayerTiling::ShouldDecodeCheckeredImagesForTile(

[vmpstr, 2017/04/20 20:59:32]

If we did end up having images on a tile earlier than we do now, then a lot of
this work could be skipped for tiles with no images at all.. Just a thought for
possible future improvements.

[Khushal, 2017/04/20 21:54:22]

May we could store an enum on Tile indicating whether it has been analyzed for
images and if it has any. This will at least avoid this for repeated runs on the
same tile.

+    const Tile* tile) const {
+  // If this is the pending tree and the tile is not occluded, any checkered
+  // images on this tile should be decoded.
+  if (tree_ == PENDING_TREE)
+    return !IsTileOccludedOnCurrentTree(tile);
+
+  DCHECK_EQ(tree_, ACTIVE_TREE);
+  const PictureLayerTiling* pending_twin =
+      client_->GetPendingOrActiveTwinTiling(this);
+
+  // If we don't have a pending twin, then 2 cases are possible. Either we don't
+  // have a pending tree, in which case we should be decoding images for tiles
+  // which are unoccluded.
+  // If we do have a pending tree, then not having a twin implies that this
+  // tiling will be evicted upon activation. TODO(khushalsagar): Plumb this
+  // information here and return false for this case.
+  if (!pending_twin)
+    return !IsTileOccludedOnCurrentTree(tile);
+
+  // If the tile will be replaced upon activation, then we don't need to process
+  // it for checkered images. Since once the pending tree is activated, it is
+  // the new active tree's content that we will invalidate and replace once the
+  // decode finishes.
+  if (!TilingMatchesTileIndices(pending_twin) ||
+      pending_twin->TileAt(tile->tiling_i_index(), tile->tiling_j_index())) {
+    return false;
+  }
+
+  // Ask the pending twin if this tile will become occluded upon activation.
+  return !pending_twin->IsTileOccludedOnCurrentTree(tile);
+}
+
 void PictureLayerTiling::UpdateRequiredStatesOnTile(Tile* tile) const {
   tile->set_required_for_activation(IsTileRequiredForActivation(tile));
   tile->set_required_for_draw(IsTileRequiredForDraw(tile));
@@ -836,7 +869,8 @@ PrioritizedTile PictureLayerTiling::MakePrioritizedTile(
        tile_priority.distance_to_visible >
            0.5f * max_skewport_extent_in_screen_space_);
   return PrioritizedTile(tile, this, tile_priority, IsTileOccluded(tile),
-                         process_for_images_only);
+                         process_for_images_only,
+                         ShouldDecodeCheckeredImagesForTile(tile));
 }
 
 std::map<const Tile*, PrioritizedTile>