Add sky-drawer to the framework

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) {
+  return 3 * a * (1 - m) * (1 - m) * m + 3 * b * (1 - m) * m * m + m * m * m

[esprehn, 2015/01/29 19:03:57]

I wonder if this is faster or slow than just using Math.pow()

[abarth-chromium, 2015/01/29 19:16:45]

I'll add a TODO comment with that question.

[abarth-chromium, 2015/01/29 19:16:45]

I'll add a TODO comment with that question.

+}
+
+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 = {
+  Cubic: Cubic,
+  linear: new Linear(),

[esprehn, 2015/01/29 19:03:57]

Why expose the Cubic class not but the Linear one?

[abarth-chromium, 2015/01/29 19:16:45]

I'll expose the Linear class.  Its constructor does't take any parameters, so
there isn't much reason to expose it.  I guess it is useful for instanceof
checks.  We need to expose the Cubic constructor so that folks can make their
own cubic curves.

+  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>