[not for review - epic CL] Adding Elastic+Momentum+Layered scrolling to views::ScrollView

ui/compositor/overscroll/ui_input_handler.cc

+// Copyright 2016 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 "ui/compositor/overscroll/ui_input_handler.h"
+
+#include "base/logging.h"
+#include "cc/trees/layer_tree_impl.h"
+#include "cc/trees/scroll_node.h"
+#include "ui/events/event.h"
+
+namespace ui {
+
+namespace {
+
+// Creates a cc::ScrollState from a ui::ScrollEvent, populating fields general
+// to all event phases. Take care not to put deltas on beginning/end updates,
+// since InputHandler will DCHECK if they're present.
+cc::ScrollState CreateScrollState(const ScrollEvent& scroll,
+                                  bool is_begin,
+                                  bool is_end) {
+  cc::ScrollStateData scroll_state_data;
+  scroll_state_data.position_x = scroll.x();
+  scroll_state_data.position_y = scroll.y();
+  if (!is_begin && !is_end) {
+    scroll_state_data.delta_x = -scroll.x_offset_ordinal();
+    scroll_state_data.delta_y = -scroll.y_offset_ordinal();
+  }
+  scroll_state_data.is_in_inertial_phase =
+      scroll.momentum_phase() == EventMomentumPhase::INERTIAL_UPDATE;
+  scroll_state_data.is_beginning = is_begin;
+  scroll_state_data.is_ending = is_end;
+  return cc::ScrollState(scroll_state_data);
+}
+
+}  // namespace
+
+UIInputHandler::UIInputHandler(
+    const base::WeakPtr<cc::InputHandler>& input_handler)
+    : input_handler_(input_handler.get()) {
+  input_handler_->BindToClient(this);
+}
+
+UIInputHandler::~UIInputHandler() {
+  DCHECK(!input_handler_);
+}
+
+void UIInputHandler::WillShutdown() {
+  input_handler_ = nullptr;
+}
+
+void UIInputHandler::Animate(base::TimeTicks time) {
+  scroll_elasticity_controller_.Animate(time);
+}
+
+void UIInputHandler::MainThreadHasStoppedFlinging() {}
+
+void UIInputHandler::ReconcileElasticOverscrollAndRootScroll() {
+  scroll_elasticity_controller_.ReconcileStretchAndScroll();
+}
+
+void UIInputHandler::UpdateRootLayerStateForSynchronousInputHandler(
+    const gfx::ScrollOffset& total_scroll_offset,
+    const gfx::ScrollOffset& max_scroll_offset,
+    const gfx::SizeF& scrollable_size,
+    float page_scale_factor,
+    float min_page_scale_factor,
+    float max_page_scale_factor) {}
+
+cc::ElementId UIInputHandler::HandleScrollBegin(const ScrollEvent& scroll) {
+  // TODO(tapted): Handle cancelling any fling or elasticity animation,
+  // ScrollUnits::Page, viewport targeting, smooth-scrolling animations. These
+  // are not currently needed for UI scrolling on Mac.
+
+  cc::ScrollState scroll_state = CreateScrollState(scroll, true, false);
+  cc::InputHandler::ScrollStatus scroll_status =
+      input_handler_->ScrollBegin(&scroll_state, cc::InputHandler::WHEEL);
+
+  switch (scroll_status.thread) {
+    case cc::InputHandler::SCROLL_ON_MAIN_THREAD:
+      // Main thread means "not here", but this should only happen if the
+      // scroll status has already entered this mode, or the scrolling layer has
+      // set main_thread_scrolling_reasons to something. Neither of which should
+      // occur for UI scrolling.
+      NOTREACHED();
+      return cc::ElementId();
+    case cc::InputHandler::SCROLL_UNKNOWN:
+      // Unknown usually means a failed hit test. Did not handle.
+      return cc::ElementId();
+    case cc::InputHandler::SCROLL_IGNORED:
+      // Something hit, but it wasn't scrollable. Ignored.
+      return cc::ElementId();
+    case cc::InputHandler::SCROLL_ON_IMPL_THREAD:
+      break;
+  }
+
+  if (!scroll_state.layer_tree_impl()) {
+    LOG(ERROR) << "layer_tree_impl not set - figure out why.";
+    return cc::ElementId();
+  }
+
+  // InputHandler::ScrollBegin() doesn't set the element ID in ScrollState. That
+  // might be nicer than reaching into LayerTreeImpl.
+  cc::LayerImpl* layer =
+      scroll_state.layer_tree_impl()->CurrentlyScrollingLayer();
+  DCHECK(layer);
+
+  // The event may be the start of a momentum portion of touchpad event stream.
+  // The input handler needs to resume scrolling, but elasticity doesn't change.
+  if ((scroll.momentum_phase() == EventMomentumPhase::MAY_BEGIN) == 0)
+    return layer->element_id();
+
+  // Lock scrolling to the thing that was hit.
+  scroll_elasticity_controller_.SetActiveHelper(
+      input_handler_->ScrollElasticityHelperForScrollingLayer());
+
+  // The elasticity controller doesn't reset when observing event streams that
+  // can't result in momentum, but that's handled above by
+  // EventMomentumPhase::MAY_BEGIN. So |leave_momentum| is just the inverse of
+  // |enter_momentum|.
+  bool has_momentum = scroll_state.is_in_inertial_phase();
+  scroll_elasticity_controller_.ObserveRealScrollBegin(has_momentum,
+                                                       !has_momentum);
+  return layer->element_id();
+}
+
+void UIInputHandler::HandleScrollUpdate(const ScrollEvent& scroll,
+                                        cc::ElementId element) {
+  // TODO(tapted): Manage animations, handle pinning a fling curve to an
+  // overscroll direction, handle did_overscroll_root. Most of these don't apply
+  // for Mac events.
+  cc::ScrollState scroll_state = CreateScrollState(scroll, false, false);
+  scroll_state.data()->set_current_native_scrolling_element(element);
+  cc::InputHandlerScrollResult result = input_handler_->ScrollBy(&scroll_state);
+
+  gfx::Vector2dF event_delta(scroll_state.delta_x(), scroll_state.delta_y());
+  scroll_elasticity_controller_.ObserveScrollUpdate(
+      event_delta, result.unused_scroll_delta, scroll.time_stamp(),
+      scroll_state.is_in_inertial_phase());
+}
+
+void UIInputHandler::HandleScrollEnd(const ScrollEvent& scroll) {
+  // TODO(tapted): Handle smooth scrolling / animations (i.e. ignore event for
+  // these cases).
+  cc::ScrollState scroll_state = CreateScrollState(scroll, false, true);
+  input_handler_->ScrollEnd(&scroll_state);
+  scroll_elasticity_controller_.ObserveRealScrollEnd(scroll.time_stamp());
+}
+
+}  // namespace ui