Move nonscrollable axis gloweffect suppression to renderer.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 685cfb99122f393eec5b610e90c35c8c51ed546d..f60df2c535024ce98feb1997dee9a6fdd5ab832b 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -2367,6 +2367,24 @@ bool LayerTreeHostImpl::ScrollBy(const gfx::Point& viewport_point,
   if (did_scroll_y)
     accumulated_root_overscroll_.set_y(0);
 
+  if (!settings_.using_synchronous_renderer_compositor) {

[jdduke (slow), 2014/04/09 17:35:00]

I don't think we want to piggyback on this setting.  We should just add a new
setting, say, |report_overscroll_only_for_scrollable_axes| (aelias@ may have a
better name), and we set it appropriately in |RenderWidgetCompositor::Create|
(for now based on the using_synchronous_renderer_compositor setting).

[aelias_OOO_until_Jul13, 2014/04/09 19:43:43]

"report_overscroll_only_for_scrollable_axes" sounds OK to me.

+    gfx::SizeF ceiled_viewport_size =
+        gfx::ToCeiledSize(active_tree_->ScrollableViewportSize());
+    gfx::SizeF root_layer_size = active_tree_->ScrollableSize();
+    if (!(ceiled_viewport_size.width() < root_layer_size.width())) {
+      // Horizontal Glow Disabled as scrolling on Horizontal axes is impossible.

[jdduke (slow), 2014/04/09 17:35:00]

I wonder if we should just use:

if (InnerViewportScrollLayer()->MaxScrollOffset().x() <= 0)
  unused_root_delta.set_x(0);

and similar for the y axis.  Then there's no need to check the other axis, and
no need to early return.  I'm not sure if we need an epsilon check; I used a
ceil previously because I was observing small float errors between viewport and
content sizes, but maybe the MaxScrollOffset does not suffer this problem
(aelias@ can you confirm?)

[aelias_OOO_until_Jul13, 2014/04/09 19:43:43]

This sounds fine.  If MaxScrollOffset suffers from the problem, we can correct
the problem there.

For future-proofing for the new pinch zoom mode, we should check
InnerViewportScrollLayer()->MaxScrollOffset().x() <= 0 &&
OuterViewportScrollLayer()->MaxScrollOffset().x() <= 0  (although only the inner
viewport is used right now).

+      if ((unused_root_delta.x() != 0 && unused_root_delta.y() == 0 &&
+           !did_scroll_x))
+        return did_scroll_content || did_scroll_top_controls;
+    }
+    if (!(ceiled_viewport_size.height() < root_layer_size.height())) {
+      // Vertical Glow Disabled as scrolling on Horizontal axes is impossible.
+      if ((unused_root_delta.x() == 0 && unused_root_delta.y() != 0 &&
+           !did_scroll_y))
+        return did_scroll_content || did_scroll_top_controls;
+    }
+  }
+
   accumulated_root_overscroll_ += unused_root_delta;
   bool did_overscroll = !unused_root_delta.IsZero();
   if (did_overscroll && input_handler_client_) {