Fix scroll position adjustment for fixed-position layers

cc/trees/layer_tree_host_common_unittest.cc

Index: cc/trees/layer_tree_host_common_unittest.cc
diff --git a/cc/trees/layer_tree_host_common_unittest.cc b/cc/trees/layer_tree_host_common_unittest.cc
index 082d14fc2c1978e232432c893a07d16b3d55e09a..d7c70e0cdaf5557fb491a11a51fa36ed8287bef2 100644
--- a/cc/trees/layer_tree_host_common_unittest.cc
+++ b/cc/trees/layer_tree_host_common_unittest.cc
@@ -8943,5 +8943,54 @@ TEST_F(LayerTreeHostCommonTest, OnlyApplyFixedPositioningOnce) {
   EXPECT_EQ(expected, fixed->visible_rect_from_property_trees());
 }
 
+TEST_F(LayerTreeHostCommonTest,
+       PropertyTreesAccountForScrollCompensationAdjustment) {
+  gfx::Transform identity;
+  gfx::Transform translate_z;
+  translate_z.Translate3d(0, 0, 10);
+
+  scoped_refptr<Layer> root = Layer::Create();
+  SetLayerPropertiesForTesting(root.get(), identity, gfx::Point3F(),
+                               gfx::PointF(), gfx::Size(800, 800), true, false);
+  root->SetIsContainerForFixedPositionLayers(true);
+
+  scoped_refptr<Layer> frame_clip = Layer::Create();
+  SetLayerPropertiesForTesting(frame_clip.get(), translate_z, gfx::Point3F(),
+                               gfx::PointF(500, 100), gfx::Size(100, 100), true,
+                               false);
+  frame_clip->SetMasksToBounds(true);
+
+  scoped_refptr<LayerWithForcedDrawsContent> scroller =
+      make_scoped_refptr(new LayerWithForcedDrawsContent());
+  SetLayerPropertiesForTesting(scroller.get(), identity, gfx::Point3F(),
+                               gfx::PointF(), gfx::Size(1000, 1000), true,
+                               false);
+
+  scroller->SetScrollCompensationAdjustment(gfx::Vector2dF(0.0, -0.5f));

[ajuma, 2015/03/26 18:03:25]

Does blink usually send negative values for scroll compensation adjustment? The
only other LayerTeeHostCommonTest for this uses the (positive) fractional
portion of scroll offset.

[Ian Vollick, 2015/03/30 17:51:25]

You're right, this is wrong. Blink sends the fractional portion of the scroll
offset (with the same sign) as the "scroll compensation adjustment". I've
updated the unit test.

+  scroller->SetScrollOffset(gfx::ScrollOffset(0.0, 0.5));
+  scroller->SetScrollClipLayerId(frame_clip->id());
+
+  scoped_refptr<LayerWithForcedDrawsContent> fixed =
+      make_scoped_refptr(new LayerWithForcedDrawsContent());
+  SetLayerPropertiesForTesting(fixed.get(), identity, gfx::Point3F(),
+                               gfx::PointF(), gfx::Size(50, 50), true, false);
+
+  LayerPositionConstraint constraint;
+  constraint.set_is_fixed_position(true);
+  fixed->SetPositionConstraint(constraint);
+
+  root->AddChild(frame_clip);
+  frame_clip->AddChild(scroller);
+  scroller->AddChild(fixed);
+
+  scoped_ptr<FakeLayerTreeHost> host(CreateFakeLayerTreeHost());
+  host->SetRootLayer(root);
+
+  ExecuteCalculateDrawProperties(root.get());
+
+  gfx::Rect expected(0, 1, 50, 49);
+  EXPECT_EQ(expected, fixed->visible_rect_from_property_trees());
+}
+
 }  // namespace
 }  // namespace cc