Hook ScrollElasticityController to InputHandlerProxy

cc/input/scroll_elasticity_helper.cc

Index: cc/input/scroll_elasticity_helper.cc
diff --git a/cc/input/scroll_elasticity_helper.cc b/cc/input/scroll_elasticity_helper.cc
new file mode 100644
index 0000000000000000000000000000000000000000..916757b99482ba6d819e07e26a147e93382e8bdd
--- /dev/null
+++ b/cc/input/scroll_elasticity_helper.cc
@@ -0,0 +1,97 @@
+// Copyright 2014 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/input/scroll_elasticity_helper.h"
+
+#include "cc/layers/layer_impl.h"
+#include "cc/trees/layer_tree_host_impl.h"
+
+namespace cc {
+
+ScrollElasticityHelper::ScrollElasticityHelper(LayerTreeHostImpl* layer_tree)
+    : layer_tree_(layer_tree), timer_active_(false) {
+}
+
+ScrollElasticityHelper::~ScrollElasticityHelper() {
+}
+
+bool ScrollElasticityHelper::AllowsHorizontalStretching() {
+  // The WebKit implementation has this interface because it is written in terms
+  // of overscrolling on a per-layer basis, not for the whole layer tree. In
+  // that implementation, this always returns true for the frame view's
+  // scrollable area.
+  // TODO(ccameron): This is function is redundant and may be removed.
+  return true;
+}
+
+bool ScrollElasticityHelper::AllowsVerticalStretching() {
+  // TODO(ccameron): This is function is redundant and may be removed.
+  return true;
+}
+
+gfx::Vector2dF ScrollElasticityHelper::StretchAmount() {
+  return stretch_offset_;
+}
+
+bool ScrollElasticityHelper::PinnedInDirection(
+    const gfx::Vector2dF& direction) {
+  LayerImpl* layer = layer_tree_->InnerViewportScrollLayer();

[aelias_OOO_until_Jul13, 2014/11/13 02:11:03]

Please use layer_tree_->TotalScrollOffset() and
layer_tree_->TotalMaxScrollOffset() instead, or this will break if/when pinch
virtual viewport ships on Mac.

[ccameron, 2014/11/13 02:45:57]

Done. Btw, I'm helping get pinch virtual viewport enabled on Mac, because I'm
writing the WebKit parts of this against it (as opposed to the deprecated
structures).

+  bool result = false;
+  if (direction.x() < 0)
+    result |= layer->TotalScrollOffset().x() <= 0;
+  if (direction.x() > 0)
+    result |= layer->TotalScrollOffset().x() >= layer->MaxScrollOffset().x();
+  if (direction.y() < 0)
+    result |= layer->TotalScrollOffset().y() <= 0;
+  if (direction.y() > 0)
+    result |= layer->TotalScrollOffset().y() >= layer->MaxScrollOffset().y();
+  return result;
+}
+
+bool ScrollElasticityHelper::CanScrollHorizontally() {
+  return layer_tree_->InnerViewportScrollLayer()->user_scrollable(HORIZONTAL);

[aelias_OOO_until_Jul13, 2014/11/13 02:11:03]

user_scrollable() just denotes whether the layer is overflow: hidden, whereupon
it can be scrolled by Javascript but not by the user.  This is  not what you
want (it's a rare condition, and can only be set on the outer viewport).  I'd
suggest instead checking if layer_tree_->TotalMaxScrollOffset().x/y() == 0.

[ccameron, 2014/11/13 02:45:57]

Thanks, done.

+}
+
+bool ScrollElasticityHelper::CanScrollVertically() {
+  return layer_tree_->InnerViewportScrollLayer()->user_scrollable(VERTICAL);
+}
+
+gfx::Vector2dF ScrollElasticityHelper::AbsoluteScrollPosition() {
+  // TODO(ccameron): This is function is redundant and may be removed.
+  return stretch_offset_;
+}
+
+void ScrollElasticityHelper::ImmediateScrollBy(const gfx::Vector2dF& scroll) {
+  // TODO(ccameron): This is function is redundant and may be removed.
+}
+
+void ScrollElasticityHelper::ImmediateScrollByWithoutContentEdgeConstraints(
+    const gfx::Vector2dF& scroll) {
+  stretch_offset_ += scroll;
+
+  // TODO(ccameron): Update the transform of the appropriate layer in the
+  // LayerTreeHostImpl, and request that a frame be drawn.
+}
+
+void ScrollElasticityHelper::StartSnapRubberbandTimer() {
+  if (timer_active_)
+    return;
+  timer_active_ = true;
+  layer_tree_->SetNeedsAnimate();
+}
+
+void ScrollElasticityHelper::StopSnapRubberbandTimer() {
+  timer_active_ = false;
+}
+
+void ScrollElasticityHelper::SnapRubberbandTimerFired() {
+  if (timer_active_)
+    layer_tree_->SetNeedsAnimate();
+}
+
+void ScrollElasticityHelper::AdjustScrollPositionToBoundsIfNecessary() {
+  // TODO(ccameron): This is function is redundant and may be removed.
+}
+
+}  // namespace cc