1 // Copyright 2014 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.
5 #include "content/child/touch_fling_gesture_curve.h"
9 #include "base/debug/trace_event.h"
10 #include "base/logging.h"
11 #include "third_party/WebKit/public/platform/WebFloatPoint.h"
12 #include "third_party/WebKit/public/platform/WebFloatSize.h"
13 #include "third_party/WebKit/public/platform/WebGestureCurve.h"
14 #include "third_party/WebKit/public/platform/WebGestureCurveTarget.h"
15 #include "third_party/WebKit/public/platform/WebSize.h"
17 using blink::WebFloatPoint;
18 using blink::WebFloatSize;
19 using blink::WebGestureCurve;
20 using blink::WebGestureCurveTarget;
25 const char* kCurveName = "TouchFlingGestureCurve";
27 // The touchpad / touchscreen fling profiles are a matched set
28 // determined via UX experimentation. Do not modify without
29 // first discussing with rjkroege@chromium.org or
30 // wjmaclean@chromium.org.
31 const float kDefaultAlpha = -5.70762e+03f;
32 const float kDefaultBeta = 1.72e+02f;
33 const float kDefaultGamma = 3.7e+00f;
35 inline double position(double t) {
36 return kDefaultAlpha * exp(-kDefaultGamma * t) - kDefaultBeta * t -
40 inline double velocity(double t) {
41 return -kDefaultAlpha * kDefaultGamma * exp(-kDefaultGamma * t) -
45 inline double timeAtVelocity(double v) {
46 return -log((v + kDefaultBeta) / (-kDefaultAlpha * kDefaultGamma)) /
55 // This curve implementation is based on the notion of a single, absolute
56 // curve, which starts at a large velocity and smoothly decreases to
57 // zero. For a given input velocity, we find where on the curve this
58 // velocity occurs, and start the animation at this point---denoted by
59 // (time_offset_, position_offset_).
61 // This has the effect of automatically determining an animation duration
62 // that scales with input velocity, as faster initial velocities start
63 // earlier on the curve and thus take longer to reach the end. No
64 // complicated time scaling is required.
66 // Since the starting velocity is implicitly determined by our starting
67 // point, we only store the relative magnitude and direction of both
68 // initial x- and y-velocities, and use this to scale the computed
69 // displacement at any point in time. This guarantees that fling
70 // trajectories are straight lines when viewed in x-y space. Initial
71 // velocities that lie outside the max velocity are constrained to start
72 // at zero (and thus are implicitly scaled).
74 // The curve is modelled as a 4th order polynomial, starting at t = 0,
75 // and ending at t = curve_duration_. Attempts to generate
76 // position/velocity estimates outside this range are undefined.
78 WebGestureCurve* TouchFlingGestureCurve::Create(
79 const WebFloatPoint& initial_velocity,
80 const WebSize& cumulative_scroll) {
81 return new TouchFlingGestureCurve(initial_velocity, cumulative_scroll);
84 TouchFlingGestureCurve::TouchFlingGestureCurve(
85 const WebFloatPoint& initial_velocity,
86 const WebSize& cumulative_scroll)
87 : cumulative_scroll_(WebFloatSize(cumulative_scroll.width,
88 cumulative_scroll.height)) {
89 DCHECK(initial_velocity != WebFloatPoint());
91 // Curve ends when velocity reaches zero.
92 curve_duration_ = timeAtVelocity(0);
93 DCHECK(curve_duration_ > 0);
95 float max_start_velocity = std::max(fabs(initial_velocity.x),
96 fabs(initial_velocity.y));
98 // Force max_start_velocity to lie in the range v(0) to v(curve_duration),
99 // and assume that the curve parameters define a monotonically decreasing
100 // velocity, or else bisection search may fail.
101 if (max_start_velocity > velocity(0))
102 max_start_velocity = velocity(0);
104 if (max_start_velocity < 0)
105 max_start_velocity = 0;
107 // We keep track of relative magnitudes and directions of the
108 // velocity/displacement components here.
109 displacement_ratio_ = WebFloatPoint(initial_velocity.x / max_start_velocity,
110 initial_velocity.y / max_start_velocity);
112 // Compute time-offset for start velocity.
113 time_offset_ = timeAtVelocity(max_start_velocity);
115 // Compute curve position at offset time
116 position_offset_ = position(time_offset_);
117 TRACE_EVENT_ASYNC_BEGIN1("input", "GestureAnimation", this, "curve",
121 TouchFlingGestureCurve::~TouchFlingGestureCurve() {
122 TRACE_EVENT_ASYNC_END0("input", "GestureAnimation", this);
125 bool TouchFlingGestureCurve::apply(double time, WebGestureCurveTarget* target) {
126 // If the fling has yet to start, simply return and report true to prevent
127 // fling termination.
133 if (time + time_offset_ < curve_duration_) {
134 displacement = position(time + time_offset_) - position_offset_;
135 speed = velocity(time + time_offset_);
137 displacement = position(curve_duration_) - position_offset_;
141 // Keep track of integer portion of scroll thus far, and prepare increment.
142 WebFloatSize scroll(displacement * displacement_ratio_.x,
143 displacement * displacement_ratio_.y);
144 WebFloatSize scroll_increment(scroll.width - cumulative_scroll_.width,
145 scroll.height - cumulative_scroll_.height);
146 WebFloatSize scroll_velocity(speed * displacement_ratio_.x,
147 speed * displacement_ratio_.y);
148 cumulative_scroll_ = scroll;
150 if (time + time_offset_ < curve_duration_ ||
151 scroll_increment != WebFloatSize()) {
152 // scrollBy() could delete this curve if the animation is over, so don't
153 // touch any member variables after making that call.
154 return target->scrollBy(scroll_increment, scroll_velocity);
160 } // namespace content