Allow perfect scroll bubbling between outer/inner viewports

cc/trees/layer_tree_host_impl_unittest.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 <cmath>
 
 #include "base/bind.h"
@@ skipping 7461 matching lines @@
     host_impl_->ScrollBy(gfx::Point(), scroll_delta);
     inner_expected += gfx::Vector2dF(scroll_delta.x(), scroll_delta.y());
 
     host_impl_->ScrollEnd();
 
     EXPECT_VECTOR_EQ(inner_expected, inner_scroll->TotalScrollOffset());
     EXPECT_VECTOR_EQ(outer_expected, outer_scroll->TotalScrollOffset());
   }
 }
 
+TEST_F(LayerTreeHostImplVirtualViewportTest,
+       DiagonalScrollBubblesPerfectlyToInner) {
+  gfx::Size content_size = gfx::Size(100, 160);
+  gfx::Size outer_viewport = gfx::Size(50, 80);
+  gfx::Size inner_viewport = gfx::Size(25, 40);
+
+  SetupVirtualViewportLayers(content_size, outer_viewport, inner_viewport);
+
+  LayerImpl* outer_scroll = host_impl_->OuterViewportScrollLayer();
+  LayerImpl* inner_scroll = host_impl_->InnerViewportScrollLayer();
+  DrawFrame();
+  {
+    gfx::Vector2dF inner_expected;
+    gfx::Vector2dF outer_expected;
+    EXPECT_VECTOR_EQ(inner_expected, inner_scroll->TotalScrollOffset());
+    EXPECT_VECTOR_EQ(outer_expected, outer_scroll->TotalScrollOffset());
+
+    // Make sure the scroll goes to the outer viewport first.
+    EXPECT_EQ(InputHandler::ScrollStarted,
+              host_impl_->ScrollBegin(gfx::Point(), InputHandler::Gesture));
+    EXPECT_EQ(InputHandler::ScrollStarted, host_impl_->FlingScrollBegin());
+
+    // Scroll near the edge of the outer viewport.
+    gfx::Vector2d scroll_delta(inner_viewport.width(), inner_viewport.height());
+    host_impl_->ScrollBy(gfx::Point(), scroll_delta);
+    outer_expected += scroll_delta;
+
+    EXPECT_VECTOR_EQ(inner_expected, inner_scroll->TotalScrollOffset());
+    EXPECT_VECTOR_EQ(outer_expected, outer_scroll->TotalScrollOffset());
+
+    // Now diagonal scroll across the outer viewport boundary in a single event.
+    // The entirety of the scroll should be consumed, as bubbling between inner
+    // and outer viewport layers is perfect.
+    host_impl_->ScrollBy(gfx::Point(), gfx::ScaleVector2d(scroll_delta, 2));
+    outer_expected += scroll_delta;
+    inner_expected += scroll_delta;
+    host_impl_->ScrollEnd();
+
+    EXPECT_VECTOR_EQ(inner_expected, inner_scroll->TotalScrollOffset());
+    EXPECT_VECTOR_EQ(outer_expected, outer_scroll->TotalScrollOffset());
+  }
+}
+
 class LayerTreeHostImplWithImplicitLimitsTest : public LayerTreeHostImplTest {
  public:
   void SetUp() override {
     LayerTreeSettings settings = DefaultSettings();
     settings.max_memory_for_prepaint_percentage = 50;
     CreateHostImpl(settings, CreateOutputSurface());
   }
 };
 
 TEST_F(LayerTreeHostImplWithImplicitLimitsTest, ImplicitMemoryLimits) {
@@ skipping 209 matching lines @@
   // surface.
   EXPECT_EQ(0, num_lost_surfaces_);
   host_impl_->DidLoseOutputSurface();
   EXPECT_EQ(1, num_lost_surfaces_);
   host_impl_->DidLoseOutputSurface();
   EXPECT_LE(1, num_lost_surfaces_);
 }
 
 }  // namespace
 }  // namespace cc