blob: cc94bd6212838ff01b1c5c91a214233a4a331f9b [file] [log] [blame]
// Copyright 2014 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 "content/child/touch_fling_gesture_curve.h"
#include <cmath>
#include "base/debug/trace_event.h"
#include "base/logging.h"
#include "third_party/WebKit/public/platform/WebFloatPoint.h"
#include "third_party/WebKit/public/platform/WebFloatSize.h"
#include "third_party/WebKit/public/platform/WebGestureCurve.h"
#include "third_party/WebKit/public/platform/WebGestureCurveTarget.h"
#include "third_party/WebKit/public/platform/WebSize.h"
using blink::WebFloatPoint;
using blink::WebFloatSize;
using blink::WebGestureCurve;
using blink::WebGestureCurveTarget;
using blink::WebSize;
namespace {
const char* kCurveName = "TouchFlingGestureCurve";
inline double position(double t, float* p) {
return p[0] * exp(-p[2] * t) - p[1] * t - p[0];
inline double velocity(double t, float* p) {
return -p[0] * p[2] * exp(-p[2] * t) - p[1];
inline double timeAtVelocity(double v, float* p) {
return -log((v + p[1]) / (-p[0] * p[2])) / p[2];
} // namespace
namespace content {
// This curve implementation is based on the notion of a single, absolute
// curve, which starts at a large velocity and smoothly decreases to
// zero. For a given input velocity, we find where on the curve this
// velocity occurs, and start the animation at this point---denoted by
// (time_offset_, position_offset_).
// This has the effect of automatically determining an animation duration
// that scales with input velocity, as faster initial velocities start
// earlier on the curve and thus take longer to reach the end. No
// complicated time scaling is required.
// Since the starting velocity is implicitly determined by our starting
// point, we only store the relative magnitude and direction of both
// initial x- and y-velocities, and use this to scale the computed
// displacement at any point in time. This guarantees that fling
// trajectories are straight lines when viewed in x-y space. Initial
// velocities that lie outside the max velocity are constrained to start
// at zero (and thus are implicitly scaled).
// The curve is modelled as a 4th order polynomial, starting at t = 0,
// and ending at t = curve_duration_. Attempts to generate
// position/velocity estimates outside this range are undefined.
WebGestureCurve* TouchFlingGestureCurve::Create(
const WebFloatPoint& initial_velocity,
float p0,
float p1,
float p2,
const WebSize& cumulative_scroll) {
return new TouchFlingGestureCurve(initial_velocity, p0, p1, p2,
const WebFloatPoint& initial_velocity,
float alpha,
float beta,
float gamma,
const WebSize& cumulative_scroll)
: cumulative_scroll_(WebFloatSize(cumulative_scroll.width,
cumulative_scroll.height)) {
DCHECK(initial_velocity != WebFloatPoint());
coefficients_[0] = alpha;
coefficients_[1] = beta;
coefficients_[2] = gamma;
// Curve ends when velocity reaches zero.
curve_duration_ = timeAtVelocity(0, coefficients_);
DCHECK(curve_duration_ > 0);
float max_start_velocity = std::max(fabs(initial_velocity.x),
// Force max_start_velocity to lie in the range v(0) to v(curve_duration),
// and assume that the curve parameters define a monotonically decreasing
// velocity, or else bisection search may fail.
if (max_start_velocity > velocity(0, coefficients_))
max_start_velocity = velocity(0, coefficients_);
if (max_start_velocity < 0)
max_start_velocity = 0;
// We keep track of relative magnitudes and directions of the
// velocity/displacement components here.
displacement_ratio_ = WebFloatPoint(initial_velocity.x / max_start_velocity,
initial_velocity.y / max_start_velocity);
// Compute time-offset for start velocity.
time_offset_ = timeAtVelocity(max_start_velocity, coefficients_);
// Compute curve position at offset time
position_offset_ = position(time_offset_, coefficients_);
TRACE_EVENT_ASYNC_BEGIN1("input", "GestureAnimation", this, "curve",
TouchFlingGestureCurve::~TouchFlingGestureCurve() {
TRACE_EVENT_ASYNC_END0("input", "GestureAnimation", this);
bool TouchFlingGestureCurve::apply(double time, WebGestureCurveTarget* target) {
// If the fling has yet to start, simply return and report true to prevent
// fling termination.
if (time <= 0)
return true;
float displacement;
float speed;
if (time + time_offset_ < curve_duration_) {
displacement =
position(time + time_offset_, coefficients_) - position_offset_;
speed = velocity(time + time_offset_, coefficients_);
} else {
displacement = position(curve_duration_, coefficients_) - position_offset_;
speed = 0.f;
// Keep track of integer portion of scroll thus far, and prepare increment.
WebFloatSize scroll(displacement * displacement_ratio_.x,
displacement * displacement_ratio_.y);
WebFloatSize scroll_increment(scroll.width - cumulative_scroll_.width,
scroll.height - cumulative_scroll_.height);
WebFloatSize scroll_velocity(speed * displacement_ratio_.x,
speed * displacement_ratio_.y);
cumulative_scroll_ = scroll;
if (time + time_offset_ < curve_duration_ ||
scroll_increment != WebFloatSize()) {
// scrollBy() could delete this curve if the animation is over, so don't
// touch any member variables after making that call.
return target->scrollBy(scroll_increment, scroll_velocity);
return false;
} // namespace content