Unity 8
KeySpline.js
1 
32 .pragma library
33 
34 function keySpline (mX1, mY1, mX2, mY2) {
35 
36  this.get = function(aX) {
37  if (mX1 == mY1 && mX2 == mY2) return aX; // linear
38  return CalcBezier(GetTForX(aX), mY1, mY2);
39  }
40 
41  function A(aA1, aA2) { return 1.0 - 3.0 * aA2 + 3.0 * aA1; }
42  function B(aA1, aA2) { return 3.0 * aA2 - 6.0 * aA1; }
43  function C(aA1) { return 3.0 * aA1; }
44 
45  // Returns x(t) given t, x1, and x2, or y(t) given t, y1, and y2.
46  function CalcBezier(aT, aA1, aA2) {
47  return ((A(aA1, aA2)*aT + B(aA1, aA2))*aT + C(aA1))*aT;
48  }
49 
50  // Returns dx/dt given t, x1, and x2, or dy/dt given t, y1, and y2.
51  function GetSlope(aT, aA1, aA2) {
52  return 3.0 * A(aA1, aA2)*aT*aT + 2.0 * B(aA1, aA2) * aT + C(aA1);
53  }
54 
55  function GetTForX(aX) {
56  // Newton raphson iteration
57  var aGuessT = aX;
58  for (var i = 0; i < 4; ++i) {
59  var currentSlope = GetSlope(aGuessT, mX1, mX2);
60  if (currentSlope == 0.0) return aGuessT;
61  var currentX = CalcBezier(aGuessT, mX1, mX2) - aX;
62  aGuessT -= currentX / currentSlope;
63  }
64  return aGuessT;
65  }
66 }