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..de3ab388a7e642c038dae8abeffe3a377acaaee6 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()->ExternalTilingRect();
     screen_space_transform_for_tile_priority_ = screen_space_transform();
   }
 
@@ -457,16 +457,27 @@ 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::ExternalTilingRect 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::Rect external_tiling_rect = layer_tree_impl()->ExternalTilingRect();
+  gfx::Transform external_tiling_transform =
+      layer_tree_impl()->ExternalTilingTransform();
+  gfx::Transform identity;
+  gfx::Transform layer_to_screen = screen_space_transform_for_tile_priority_;
+  layer_to_screen.ConcatTransform(external_tiling_transform);

[aelias_OOO_until_Jul13, 2014/07/16 21:23:31]

Please bake it into screen_space_transform_for_tile_priority_ inside
UpdateTiles() instead.

[hush (inactive), 2014/07/17 00:05:53]

Done.

+  if (visible_rect_in_content_space.IsEmpty() ||
+      layer_tree_impl()->DrawViewportSize() != external_tiling_rect.size() ||

[aelias_OOO_until_Jul13, 2014/07/16 21:23:31]

Please cast the DrawViewportSize to a rect instead.  Right now, this is missing
the case where the size is the same but the rect position is nonzero.

[hush (inactive), 2014/07/17 00:05:53]

Yes, indeed it is missing that case.
I will use DeviceViewport()
On 2014/07/16 21:23:31, aelias wrote:

+      !external_tiling_transform.IsIdentity()) {
     gfx::Transform screen_to_layer(gfx::Transform::kSkipInitialization);
-    if (screen_space_transform_for_tile_priority_.GetInverse(
-            &screen_to_layer)) {
-      visible_rect_in_content_space =
-          gfx::ToEnclosingRect(MathUtil::ProjectClippedRect(
-              screen_to_layer, gfx::Rect(viewport_size_for_tile_priority_)));
+
+    if (layer_to_screen.GetInverse(&screen_to_layer)) {
+      // Transform from view space to content space.
+      visible_rect_in_content_space = gfx::ToEnclosingRect(
+          MathUtil::ProjectClippedRect(screen_to_layer, external_tiling_rect));
+
       visible_rect_in_content_space.Intersect(gfx::Rect(content_bounds()));
     }
   }