ui/views/animation/scroll_animator.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "ui/views/animation/scroll_animator.h"
   6
   7 #include <algorithm>
   8 #include <cmath>
   9
  10 #include "base/logging.h"
  11 #include "ui/gfx/animation/slide_animation.h"
  12
  13 namespace {
  14 const float kDefaultAcceleration = -1500.0f; // in pixels per second^2
  15
  16 // Assumes that d0 == 0.0f
  17 float GetPosition(float v0, float a, float t) {
  18   float max_t = -v0 / a;
  19   if (t > max_t)
  20     t = max_t;
  21   return t * (v0 + 0.5f * a * t);
  22 }
  23
  24 float GetDelta(float v0, float a, float t1, float t2) {
  25   return GetPosition(v0, a, t2) - GetPosition(v0, a, t1);
  26 }
  27
  28 }  // namespace
  29
  30 namespace views {
  31
  32 ScrollAnimator::ScrollAnimator(ScrollDelegate* delegate)
  33   : delegate_(delegate),
  34     velocity_x_(0.0f),
  35     velocity_y_(0.0f),
  36     last_t_(0.0f),
  37     duration_(0.0f),
  38     acceleration_(kDefaultAcceleration) {
  39   DCHECK(delegate);
  40 }
  41
  42 ScrollAnimator::~ScrollAnimator() {
  43   Stop();
  44 }
  45
  46 void ScrollAnimator::Start(float velocity_x, float velocity_y) {
  47   if (acceleration_ >= 0.0f)
  48     acceleration_ = kDefaultAcceleration;
  49   float v = std::max(fabs(velocity_x), fabs(velocity_y));
  50   last_t_ = 0.0f;
  51   velocity_x_ = velocity_x;
  52   velocity_y_ = velocity_y;
  53   duration_ = -v / acceleration_; // in seconds
  54   animation_.reset(new gfx::SlideAnimation(this));
  55   animation_->SetSlideDuration(static_cast<int>(duration_ * 1000));
  56   animation_->Show();
  57 }
  58
  59 void ScrollAnimator::Stop() {
  60   velocity_x_ = velocity_y_ = last_t_ = duration_ = 0.0f;
  61   animation_.reset();
  62 }
  63
  64 void ScrollAnimator::AnimationEnded(const gfx::Animation* animation) {
  65   Stop();
  66 }
  67
  68 void ScrollAnimator::AnimationProgressed(const gfx::Animation* animation) {
  69   float t = static_cast<float>(animation->GetCurrentValue()) * duration_;
  70   float a_x = velocity_x_ > 0 ? acceleration_ : -acceleration_;
  71   float a_y = velocity_y_ > 0 ? acceleration_ : -acceleration_;
  72   float dx = GetDelta(velocity_x_, a_x, last_t_, t);
  73   float dy = GetDelta(velocity_y_, a_y, last_t_, t);
  74   last_t_ = t;
  75   delegate_->OnScroll(dx, dy);
  76 }
  77
  78 void ScrollAnimator::AnimationCanceled(const gfx::Animation* animation) {
  79   Stop();
  80 }
  81
  82 }  // namespace views