Support touch scroll gestures in menus.

ui/views/animation/scroll_animator.cc

+// Copyright (c) 2011 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/views/animation/scroll_animator.h"
+
+#include <algorithm>
+#include <cmath>
+
+#include "base/logging.h"
+#include "ui/base/animation/slide_animation.h"
+
+namespace {
+const float kDefaultAcceleration = -1500.0f; // in pixels per second^2
+
+// Assumes that d0 == 0.0f
+float GetPosition(float v0, float a, float t) {
+  float max_t = -v0 / a;
+  if (t > max_t)
+    t = max_t;
+  return t * (v0 + 0.5f * a * t);
+}
+
+float GetDelta(float v0, float a, float t1, float t2) {
+  return GetPosition(v0, a, t2) - GetPosition(v0, a, t1);
+}
+
+}  // namespace
+
+namespace views {
+
+ScrollAnimator::ScrollAnimator(ScrollDelegate* delegate)
+  : delegate_(delegate),
+    velocity_x_(0.0f),
+    velocity_y_(0.0f),
+    last_t_(0.0f),
+    duration_(0.0f),
+    acceleration_(kDefaultAcceleration) {
+  DCHECK(delegate);
+}
+
+ScrollAnimator::~ScrollAnimator() {
+  Stop();
+}
+
+void ScrollAnimator::Start(float velocity_x, float velocity_y) {
+  if (acceleration_ >= 0.0f)
+    acceleration_ = kDefaultAcceleration;
+  float v = std::max(fabs(velocity_x), fabs(velocity_y));
+  last_t_ = 0.0f;
+  velocity_x_ = velocity_x;
+  velocity_y_ = velocity_y;
+  duration_ = -v / acceleration_; // in seconds
+  animation_.reset(new ui::SlideAnimation(this));
+  animation_->SetSlideDuration(static_cast<int>(duration_ * 1000));
+  animation_->Show();
+}
+
+void ScrollAnimator::Stop() {
+  velocity_x_ = velocity_y_ = last_t_ = duration_ = 0.0f;
+  animation_.reset();
+}
+
+void ScrollAnimator::AnimationEnded(const ui::Animation* animation) {
+  Stop();
+}
+
+void ScrollAnimator::AnimationProgressed(const ui::Animation* animation) {
+  float t = static_cast<float>(animation->GetCurrentValue()) * duration_;
+  float a_x = velocity_x_ > 0 ? acceleration_ : -acceleration_;
+  float a_y = velocity_y_ > 0 ? acceleration_ : -acceleration_;
+  float dx = GetDelta(velocity_x_, a_x, last_t_, t);
+  float dy = GetDelta(velocity_y_, a_y, last_t_, t);
+  last_t_ = t;
+  delegate_->OnScroll(dx, dy);
+}
+
+void ScrollAnimator::AnimationCanceled(const ui::Animation* animation) {
+  Stop();
+}
+
+}  // namespace views
+