sky/framework/animation/curves.sky

<!--
// Copyright 2015 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.
-->
<script>
function evaluateCubic(a, b, m) {
  // TODO(abarth): Would Math.pow be faster?
  return 3 * a * (1 - m) * (1 - m) * m + 3 * b * (1 - m) * m * m + m * m * m
}

const kCubicErrorBound = 0.001;

class Linear {
  transform(t) {
    return t;
  }
};

class Cubic {
  constructor(a, b, c, d) {
    this.a_ = a;
    this.b_ = b;
    this.c_ = c;
    this.d_ = d;
    Object.preventExtensions(this);
  }

  transform(t) {
    var start = 0, end = 1;
    while (1) {
      var midpoint = (start + end) / 2;
      var estimate = evaluateCubic(this.a_, this.c_, midpoint);

      if (Math.abs(t - estimate) < kCubicErrorBound)
        return evaluateCubic(this.b_, this.d_, midpoint);

      if (estimate < t)
        start = midpoint;
      else
        end = midpoint;
    }
  }
}

module.exports = {
  Linear: Linear,
  Cubic: Cubic,
  linear: new Linear(),
  ease: new Cubic(0.25, 0.1, 0.25, 1),
  easeIn: new Cubic(0.42, 0, 1, 1),
  easeOut: new Cubic(0, 0, 0.58, 1),
  easeInOut: new Cubic(0.42, 0, 0.58, 1),
};
</script>