Adding momentum/overscroll to views:: ScrollViews

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 "ui/events/event.h"
+
+namespace ui {
+
+namespace {
+
+// Populate fields general to all event phases. Beginning/end isn't read by the
+// InputHandler, but it will get upset if deltas are put on those updates.
+cc::ScrollState CreateScrollState(const ScrollEvent& scroll,
+                                  bool begin,
+                                  bool end) {
+  cc::ScrollStateData scroll_state_data;
+  scroll_state_data.position_x = scroll.x();
+  scroll_state_data.position_y = scroll.y();
+  if (!begin && !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() & EM_PHASE_INERTIAL_UPDATE) != 0;
+  scroll_state_data.is_beginning = begin;
+  scroll_state_data.is_ending = 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_ = NULL;
+}
+
+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) {}
+
+void UIInputHandler::HandleScrollBegin(const ScrollEvent& scroll) {
+  // Not handled: Cancelling a any fling or elasticity animation,
+  // ScrollUnits::Page, viewport targeting, smooth-scrolling animations. These
+  // aren't currently needed for UI scrolling on Mac.
+
+  cc::ScrollState scroll_state = CreateScrollState(scroll, true, false);
+  // Communicate a "resume" to the input handler by calling ScrollBegin with
+  // ScrollStateData::is_beginning set to false.
+  if ((scroll.momentum_phase() &
+       (EM_PHASE_INERTIAL_UPDATE | EM_PHASE_MAY_BEGIN)) ==
+      EM_PHASE_INERTIAL_UPDATE)
+    scroll_state.set_is_beginning(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;
+    case cc::InputHandler::SCROLL_UNKNOWN:
+      return;  // Unknown usually means a failed hit test. Did not handle.
+    case cc::InputHandler::SCROLL_IGNORED:
+      return;  // Something hit, but it wasn't scrollable. Ignored.
+    case cc::InputHandler::SCROLL_ON_IMPL_THREAD:
+      break;
+  }
+
+  // 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() & EM_PHASE_MAY_BEGIN) == 0)
+    return;
+
+  // 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 EM_PHASE_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);
+}
+
+void UIInputHandler::HandleScrollUpdate(const ScrollEvent& scroll) {
+  // Not handled: Early-exit if nothing was hit earlier, animation management,
+  // pinning a fling curve to an overscroll direction, did_overscroll_root.
+  cc::ScrollState scroll_state = CreateScrollState(scroll, false, false);
+  gfx::Point scroll_point(scroll_state.position_x(), scroll_state.position_y());
+  cc::InputHandlerScrollResult scroll_result =
+      input_handler_->ScrollBy(&scroll_state);
+
+  gfx::Vector2dF event_delta(scroll_state.delta_x(), scroll_state.delta_y());
+  scroll_elasticity_controller_.ObserveScrollUpdate(
+      event_delta, scroll_result.unused_scroll_delta, scroll.time_stamp(),
+      scroll_state.is_in_inertial_phase());
+}
+
+void UIInputHandler::HandleScrollEnd(const ScrollEvent& scroll) {
+  // Not handled: Smooth scrolling / animations (i.e. ignore event).
+  cc::ScrollState scroll_state = CreateScrollState(scroll, false, true);
+  input_handler_->ScrollEnd(&scroll_state);
+  scroll_elasticity_controller_.ObserveRealScrollEnd(scroll.time_stamp());
+}
+
+}  // namespace ui