Adds bounce and elastic easing to animation curves

packages/flutter/lib/animation/curves.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:math' as math;
+
 double _evaluateCubic(double a, double b, double 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;
@@ -79,6 +81,84 @@ class Cubic implements Curve {
   }
 }
 
+double _bounce(double t)
+{
+  if (t < 1.0 / 2.75) {
+    return 7.5625 * t * t;
+  } else if (t < 2 / 2.75) {
+    t -= 1.5 / 2.75;
+    return 7.5625 * t * t + 0.75;
+  } else if (t < 2.5 / 2.75) {
+    t -= 2.25 / 2.75;
+    return 7.5625 * t * t + 0.9375;
+  }
+  t -= 2.625 / 2.75;
+  return 7.5625 * t * t + 0.984375;
+}
+
+class BounceInCurve implements Curve {
+  const BounceInCurve();
+
+  double transform(double t) {
+    return 1.0 - _bounce(1.0 - t);
+  }
+}
+
+class BounceOutCurve implements Curve {
+  const BounceOutCurve();
+
+  double transform(double t) {
+    return _bounce(t);
+  }
+}
+
+class BounceInOutCurve implements Curve {
+  const BounceInOutCurve();
+
+  double transform(double t) {
+    if (t < 0.5)
+      return (1.0 - _bounce(1.0 - t)) * 0.5;
+    else
+      return _bounce(t * 2.0 - 1.0) * 0.5 + 0.5;
+  }
+}
+
+class ElasticInCurve implements Curve {
+  const ElasticInCurve([this.period = 0.4]);
+  final double period;
+
+  double transform(double t) {
+    double s = period / 4.0;
+    t = t - 1.0;
+    return -math.pow(2.0, 10.0 * t) * math.sin((t - s) * (math.PI * 2.0) / period);
+  }
+}
+
+class ElasticOutCurve implements Curve {
+  const ElasticOutCurve([this.period = 0.4]);
+  final double period;
+
+  double transform(double t) {
+    double s = period / 4.0;
+    return math.pow(2.0, -10 * t) * math.sin((t - s) * (math.PI * 2.0) / period) + 1.0;
+  }
+}
+
+class ElasticInOutCurve implements Curve {
+  const ElasticInOutCurve([this.period = 0.4]);
+  final double period;
+
+  double transform(double t) {
+    t = t * 2;
+    double s = period / 4.0;
+    t = t - 1.0;
+    if (t < 0.0)
+      return -0.5 * math.pow(2.0, 10.0 * t) * math.sin((t - s) * (math.PI * 2.0) / period);
+    else
+      return math.pow(2.0, -10.0 * t) * math.sin((t - s) * (math.PI * 2.0) / period) * 0.5 + 1.0;
+  }
+}
+
 const Linear linear = const Linear();
 const Cubic ease = const Cubic(0.25, 0.1, 0.25, 1.0);
 const Cubic easeIn = const Cubic(0.42, 0.0, 1.0, 1.0);
@@ -86,3 +166,9 @@ const Cubic easeOut = const Cubic(0.0, 0.0, 0.58, 1.0);
 const Cubic easeInOut = const Cubic(0.42, 0.0, 0.58, 1.0);
 const ParabolicRise parabolicRise = const ParabolicRise();
 const ParabolicFall parabolicFall = const ParabolicFall();
+const BounceInCurve bounceIn = const BounceInCurve();
+const BounceOutCurve bounceOut = const BounceOutCurve();
+const BounceInOutCurve bounceInOut = const BounceInOutCurve();
+const ElasticInCurve elasticIn = const ElasticInCurve();
+const ElasticOutCurve elasticOut = const ElasticOutCurve();
+const ElasticInOutCurve elasticInOut = const ElasticInOutCurve();