Consolidate content fling implementations

content/child/touch_fling_gesture_curve.cc

-// 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";
-
-// The touchpad / touchscreen fling profiles are a matched set
-// determined via UX experimentation. Do not modify without
-// first discussing with rjkroege@chromium.org or
-// wjmaclean@chromium.org.
-const float kDefaultAlpha = -5.70762e+03f;
-const float kDefaultBeta = 1.72e+02f;
-const float kDefaultGamma = 3.7e+00f;
-
-inline double position(double t) {
-  return kDefaultAlpha * exp(-kDefaultGamma * t) - kDefaultBeta * t -
-         kDefaultAlpha;
-}
-
-inline double velocity(double t) {
-  return -kDefaultAlpha * kDefaultGamma * exp(-kDefaultGamma * t) -
-         kDefaultBeta;
-}
-
-inline double timeAtVelocity(double v) {
-  return -log((v + kDefaultBeta) / (-kDefaultAlpha * kDefaultGamma)) /
-         kDefaultGamma;
-}
-
-} // 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,
-    const WebSize& cumulative_scroll) {
-  return new TouchFlingGestureCurve(initial_velocity, cumulative_scroll);
-}
-
-TouchFlingGestureCurve::TouchFlingGestureCurve(
-    const WebFloatPoint& initial_velocity,
-    const WebSize& cumulative_scroll)
-    : cumulative_scroll_(WebFloatSize(cumulative_scroll.width,
-                                      cumulative_scroll.height)) {
-  DCHECK(initial_velocity != WebFloatPoint());
-
-  // Curve ends when velocity reaches zero.
-  curve_duration_ = timeAtVelocity(0);
-  DCHECK(curve_duration_ > 0);
-
-  float max_start_velocity = std::max(fabs(initial_velocity.x),
-                                      fabs(initial_velocity.y));
-
-  // 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))
-    max_start_velocity = velocity(0);
-
-  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);
-
-  // Compute curve position at offset time
-  position_offset_ = position(time_offset_);
-  TRACE_EVENT_ASYNC_BEGIN1("input", "GestureAnimation", this, "curve",
-      kCurveName);
-}
-
-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_) - position_offset_;
-    speed = velocity(time + time_offset_);
-  } else {
-    displacement = position(curve_duration_) - 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