Move nonscrollable axis gloweffect suppression to renderer.

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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/trees/layer_tree_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/basictypes.h"
@@ skipping 2291 matching lines @@
           ScrollLayerWithViewportSpaceDelta(layer_impl,
                                             scale_from_viewport_to_screen_space,
                                             viewport_point, pending_delta);
     } else {
       applied_delta = ScrollLayerWithLocalDelta(layer_impl, pending_delta);
     }
 
     const float kEpsilon = 0.1f;
     if (layer_impl == InnerViewportScrollLayer()) {
       unused_root_delta.Subtract(applied_delta);
       if (std::abs(unused_root_delta.x()) < kEpsilon)

[jdduke (slow), 2014/04/09 22:51:48]

It might make sense for us to move the zero-ing code here, so that all such code
is in a single place in this function.

         unused_root_delta.set_x(0.0f);
       if (std::abs(unused_root_delta.y()) < kEpsilon)
         unused_root_delta.set_y(0.0f);
     }
 
     // If the layer wasn't able to move, try the next one in the hierarchy.
     bool did_move_layer_x = std::abs(applied_delta.x()) > kEpsilon;
     bool did_move_layer_y = std::abs(applied_delta.y()) > kEpsilon;
     did_scroll_x |= did_move_layer_x;
     did_scroll_y |= did_move_layer_y;
@@ skipping 37 matching lines @@
     SetNeedsRedraw();
     client_->RenewTreePriority();
   }
 
   // Scrolling along an axis resets accumulated root overscroll for that axis.
   if (did_scroll_x)
     accumulated_root_overscroll_.set_x(0);
   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_) {
     input_handler_client_->DidOverscroll(accumulated_root_overscroll_,
                                          unused_root_delta);
   }
 
   return did_scroll_content || did_scroll_top_controls;
 }
 
@@ skipping 687 matching lines @@
   swap_promise_monitor_.erase(monitor);
 }
 
 void LayerTreeHostImpl::NotifySwapPromiseMonitorsOfSetNeedsRedraw() {
   std::set<SwapPromiseMonitor*>::iterator it = swap_promise_monitor_.begin();
   for (; it != swap_promise_monitor_.end(); it++)
     (*it)->OnSetNeedsRedrawOnImpl();
 }
 
 }  // namespace cc