Scroll with Layers in views::ScrollView

ui/compositor/layer.cc

Index: ui/compositor/layer.cc
diff --git a/ui/compositor/layer.cc b/ui/compositor/layer.cc
index 7dcf17724f2ca838e763b2198a5a347d6f13a22a..22f162381d67866ab4131d730fd5261154a2c5c4 100644
--- a/ui/compositor/layer.cc
+++ b/ui/compositor/layer.cc
@@ -756,6 +756,36 @@ void Layer::OnDelegatedFrameDamage(const gfx::Rect& damage_rect_in_dip) {
   delegate_->OnDelegatedFrameDamage(damage_rect_in_dip);
 }
 
+void Layer::SetScrollable(Layer* parent_clip_layer,
+                          const base::Closure& on_scroll) {
+  cc_layer_->SetScrollParent(parent_clip_layer->cc_layer_);

[Ian Vollick, 2016/08/09 14:00:49]

This should not be necessary. The concept of "scroll parent" is very weird and
should only be used for web content.

[tapted, 2016/08/10 05:39:04]

Done.

+  cc_layer_->SetIsContainerForFixedPositionLayers(true);

[Ian Vollick, 2016/08/09 14:00:49]

Do we used fixed pos layers in ui::?

[tapted, 2016/08/10 05:39:04]

Ah, I must have added this in a very early iteration that tried to swap the
scrolling layer with the layer tree host's inner_viewport_scroll_layer_ on each
scroll event. There's a DCHECK in LayerTreeHost::FinishCommitOnImplThread that
would fail. But I don't think I need it now - this doesn't seem to get used on
the impl side. Removed.

+  cc_layer_->SetScrollClipLayerId(parent_clip_layer->cc_layer_->id());
+  cc_layer_->set_did_scroll_callback(on_scroll);
+  cc_layer_->SetUserScrollable(true, true);
+}
+
+gfx::ScrollOffset Layer::CurrentScrollOffset() const {
+  const Compositor* compositor = GetCompositor();
+  gfx::ScrollOffset offset;
+  if (compositor &&
+      compositor->GetScrollOffsetForLayer(cc_layer_->id(), &offset))
+    return offset;
+  return cc_layer_->scroll_offset();
+}
+
+void Layer::SetScrollOffset(const gfx::ScrollOffset& offset) {
+  Compositor* compositor = GetCompositor();
+  bool scrolled_on_impl_side =
+      compositor && compositor->ScrollLayerTo(cc_layer_->id(), offset);
+
+  if (!scrolled_on_impl_side)
+    cc_layer_->SetScrollOffset(offset);
+
+  DCHECK_EQ(offset.x(), CurrentScrollOffset().x());
+  DCHECK_EQ(offset.y(), CurrentScrollOffset().y());
+}
+
 void Layer::RequestCopyOfOutput(
     std::unique_ptr<cc::CopyOutputRequest> request) {
   cc_layer_->RequestCopyOfOutput(std::move(request));