Tiling priorities in Android Webview.

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index 02fb92fb735dce8d5048487eebe38ab6800c7706..f30fa88445bc4cd069c6c9a98dda61ebea1ff725 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -399,7 +399,7 @@ void PictureLayerImpl::UpdateTiles(
   // resourceless software draw, so don't update them.
   if (!layer_tree_impl()->resourceless_software_draw()) {
     visible_rect_for_tile_priority_ = visible_content_rect();
-    viewport_size_for_tile_priority_ = layer_tree_impl()->DrawViewportSize();
+    viewport_rect_for_tile_priority_ = layer_tree_impl()->TilingViewportRect();
     screen_space_transform_for_tile_priority_ = screen_space_transform();
   }
 
@@ -457,16 +457,28 @@ void PictureLayerImpl::UpdateTilePriorities(
   if (!tiling_needs_update)
     return;
 
-  // Use visible_content_rect, unless it's empty. If it's empty, then
-  // try to inverse project the viewport into layer space and use that.
+  // If visible_rect_for_tile_priority_ is empty or
+  // LayerTreeImpl::TilingViewportRect is set to be different from the device
+  // viewport, try to inverse project the viewport into layer space and use
+  // that. Otherwise just use visible_rect_for_tile_priority_
   gfx::Rect visible_rect_in_content_space = visible_rect_for_tile_priority_;
-  if (visible_rect_in_content_space.IsEmpty()) {
-    gfx::Transform screen_to_layer(gfx::Transform::kSkipInitialization);
-    if (screen_space_transform_for_tile_priority_.GetInverse(
-            &screen_to_layer)) {
+  if (visible_rect_in_content_space.IsEmpty() ||
+      layer_tree_impl()->DrawViewportSize() !=
+          layer_tree_impl()->TilingViewportRect().size()) {
+    gfx::Transform view_to_layer(gfx::Transform::kSkipInitialization);
+    gfx::Transform screen_to_view(gfx::Transform::kSkipInitialization);
+    if (screen_space_transform_for_tile_priority_.GetInverse(&view_to_layer) &&
+        layer_tree_impl()->TilingTransform().GetInverse(&screen_to_view)) {

[boliu, 2014/07/16 17:25:10]

I assume this should only be read when
!layer_tree_impl()->resourceless_software_draw() ?

[hush (inactive), 2014/07/16 20:45:33]

In resourceless software draw, the transform is identity and DrawViewportSize()
is equal to TilingViewportSize(). So this if condition will fail.

On 2014/07/16 17:25:10, boliu wrote:

+      // Transform the tiling viewport rect from screen to view space.
+      gfx::Rect viewport_rect_in_view_space =
+          gfx::ToEnclosingRect(MathUtil::ProjectClippedRect(
+              screen_to_view, layer_tree_impl()->TilingViewportRect()));
+
+      // Transform from view space to content space.
       visible_rect_in_content_space =
           gfx::ToEnclosingRect(MathUtil::ProjectClippedRect(
-              screen_to_layer, gfx::Rect(viewport_size_for_tile_priority_)));
+              view_to_layer, viewport_rect_in_view_space));
+
       visible_rect_in_content_space.Intersect(gfx::Rect(content_bounds()));
     }
   }