Avoid unnecessary gloweffect calls

When there's some overscroll in the x axis (getting us past the rounding check) and
an epsilon of overscroll in the y axis due to numerical error, this later convinces
OverscrollGlow to trigger the fling glow in that direction.  The Rounded check only
protected us against epsilons in *both* directions.  Replace this with removing
the epsilon explicitly in unused_scroll_delta.

BUG=354325

Review URL: https://codereview.chromium.org/206153002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@259729 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 45 insertions, 2 deletions

diff --git a/AUTHORS b/AUTHORS
index f1e25bf..a1e27b3 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -315,6 +315,7 @@ Song YeWen <ffmpeg@gmail.com>
 Soren Dreijer <dreijerbit@gmail.com>
 Stephen Searles <stephen.searles@gmail.com>
 Steven Pennington <spenn@engr.uvic.ca>
+Subrahmanya Praveen Munukutla <sataya.m@samsung.com>
 Suchit Agrawal <a.suchit@samsung.com>
 Sudarsana Babu Nagineni <sudarsana.nagineni@intel.com>
 Sudarshan Parthasarathy <sudarshan.p@samsung.com>
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 7422dc9..f4054fd1 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -2268,8 +2268,14 @@ bool LayerTreeHostImpl::ScrollBy(const gfx::Point& viewport_point,
         break;
     }
 
-    if (layer_impl == InnerViewportScrollLayer())
+    if (layer_impl == InnerViewportScrollLayer()) {
       unused_root_delta.Subtract(applied_delta);
+      const float kOverscrollEpsilon = 0.01f;
+      if (std::abs(unused_root_delta.x()) < kOverscrollEpsilon)
+        unused_root_delta.set_x(0.0f);
+      if (std::abs(unused_root_delta.y()) < kOverscrollEpsilon)
+        unused_root_delta.set_y(0.0f);
+    }
 
     did_lock_scrolling_layer_ = true;
     if (!should_bubble_scrolls_) {
@@ -2310,7 +2316,7 @@ bool LayerTreeHostImpl::ScrollBy(const gfx::Point& viewport_point,
     accumulated_root_overscroll_.set_y(0);
 
   accumulated_root_overscroll_ += unused_root_delta;
-  bool did_overscroll = !gfx::ToRoundedVector2d(unused_root_delta).IsZero();
+  bool did_overscroll = !unused_root_delta.IsZero();
   if (did_overscroll && input_handler_client_) {
     DidOverscrollParams params;
     params.accumulated_overscroll = accumulated_root_overscroll_;
diff --git a/cc/trees/layer_tree_host_impl_unittest.cc b/cc/trees/layer_tree_host_impl_unittest.cc
index 37f2cd5..59d819b 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -3162,6 +3162,42 @@ TEST_F(LayerTreeHostImplTest, OverscrollAlways) {
   EXPECT_EQ(gfx::Vector2dF(), host_impl_->current_fling_velocity());
 }
 
+TEST_F(LayerTreeHostImplTest, UnnecessaryGlowEffectCallsWhileScrollingUp) {
+  // Edge glow effect should be applicable only upon reaching Edges
+  // of the content. unnecessary glow effect calls shouldn't be
+  // called while scrolling up without reaching the edge of the content.
+  gfx::Size surface_size(100, 100);
+  gfx::Size content_size(200, 200);
+  scoped_ptr<LayerImpl> root_clip =
+      LayerImpl::Create(host_impl_->active_tree(), 3);
+  scoped_ptr<LayerImpl> root =
+      CreateScrollableLayer(1, content_size, root_clip.get());
+  root->SetIsContainerForFixedPositionLayers(true);
+  scoped_ptr<LayerImpl> child =
+      CreateScrollableLayer(2, content_size, root_clip.get());
+
+  child->SetScrollClipLayer(Layer::INVALID_ID);
+  root->AddChild(child.Pass());
+  root_clip->AddChild(root.Pass());
+
+  host_impl_->SetViewportSize(surface_size);
+  host_impl_->active_tree()->SetRootLayer(root_clip.Pass());
+  host_impl_->active_tree()->SetViewportLayersFromIds(3, 1, Layer::INVALID_ID);
+  host_impl_->active_tree()->DidBecomeActive();
+  DrawFrame();
+  {
+    EXPECT_EQ(InputHandler::ScrollStarted,
+              host_impl_->ScrollBegin(gfx::Point(0, 0), InputHandler::Wheel));
+    host_impl_->ScrollBy(gfx::Point(), gfx::Vector2dF(0, 100));
+    EXPECT_EQ(gfx::Vector2dF().ToString(),
+              host_impl_->accumulated_root_overscroll().ToString());
+    host_impl_->ScrollBy(gfx::Point(), gfx::Vector2dF(0, -2.30f));
+    EXPECT_EQ(gfx::Vector2dF().ToString(),
+              host_impl_->accumulated_root_overscroll().ToString());
+    host_impl_->ScrollEnd();
+  }
+}
+
 class BlendStateCheckLayer : public LayerImpl {
  public:
   static scoped_ptr<LayerImpl> Create(LayerTreeImpl* tree_impl,