Merge branch 'master' of github.com:domokit/sky_engine

sky/packages/sky/lib/animation/forces.dart

@@ -13,22 +13,25 @@ abstract class Force {
 class SpringForce extends Force {
   SpringForce(this.spring, {this.left: 0.0, this.right: 1.0});
 
+  // We overshoot the target by this distance, but stop the simulation when
+  // the spring gets within this distance (regardless of how fast it's moving).
+  // This causes the spring to settle a bit faster than it otherwise would.
+  static final Tolerance tolerance =
+      new Tolerance(velocity: double.INFINITY, distance: 0.01);
+
   final SpringDescription spring;
   // Where to put the spring's resting point when releasing left or right,
   // respectively.
   final double left, right;
 
   Simulation release(double position, double velocity, Direction direction) {
-    // Target just past the endpoint, because the animation will stop once the
-    // Spring gets within the epsilon, and we want to stop at the endpoint.
     double target = direction == Direction.reverse ?
-        this.left - _kEpsilon : this.right + _kEpsilon;
-    return new SpringSimulation(spring, position, target, velocity);
+        this.left - tolerance.distance : this.right + tolerance.distance;
+    return new SpringSimulation(spring, position, target, velocity)
+      ..tolerance = tolerance;
   }
 }
 
 final SpringDescription _kDefaultSpringDesc =
     new SpringDescription.withDampingRatio(mass: 1.0, springConstant: 500.0, ratio: 1.0);
 final SpringForce kDefaultSpringForce = new SpringForce(_kDefaultSpringDesc);
-
-const double _kEpsilon = 0.001;