feat(DecayAnimation): Adds decay animation driver (microsoft#636)

rozele · web-flow · commit 9edac68d9bf2 · 2016-08-25T15:35:53.000-04:00
diff --git a/ReactWindows/ReactNative/Animated/DecayAnimationDriver.cs b/ReactWindows/ReactNative/Animated/DecayAnimationDriver.cs
@@ -0,0 +1,48 @@
+﻿using Newtonsoft.Json.Linq;
+using ReactNative.Bridge;
+using System;
+
+namespace ReactNative.Animated
+{
+    class DecayAnimationDriver : AnimationDriver
+    {
+        private readonly double _velocity;
+        private readonly double _deceleration;
+
+        private long _startFrameTimeMillis = -1;
+        private double _fromValue;
+        private double _lastValue;
+
+        public DecayAnimationDriver(int id, ValueAnimatedNode animatedValue, ICallback endCallback, JObject config)
+            : base(id, animatedValue, endCallback)
+        {
+            _velocity = config.Value<double>("velocity");
+            _deceleration = config.Value<double>("deceleration");
+        }
+
+        public override void RunAnimationStep(TimeSpan renderingTime)
+        {
+            long frameTimeMillis = renderingTime.Ticks / 10000;
+            if (_startFrameTimeMillis == -1)
+            {
+                // since this is the first animation step, consider the start to be on the previous frame
+                _startFrameTimeMillis = frameTimeMillis - 16;
+                _fromValue = AnimatedValue.Value;
+                _lastValue = AnimatedValue.Value;
+            }
+
+            var value = _fromValue +
+                (_velocity / (1 - _deceleration)) *
+                    (1 - Math.Exp(-(1 - _deceleration) * (frameTimeMillis - _startFrameTimeMillis)));
+
+            if (Math.Abs(_lastValue - value) < 0.1)
+            {
+                HasFinished = true;
+                return;
+            }
+
+            _lastValue = value;
+            AnimatedValue.Value = value;
+        }
+    }
+}
diff --git a/ReactWindows/ReactNative/Animated/NativeAnimatedNodesManager.cs b/ReactWindows/ReactNative/Animated/NativeAnimatedNodesManager.cs
@@ -155,6 +155,9 @@ public void StartAnimatingNode(int animationId, int animatedNodeTag, JObject ani
             var animation = default(AnimationDriver);
             switch (type)
             {
+                case "decay":
+                    animation = new DecayAnimationDriver(animationId, valueNode, endCallback, animationConfig);
+                    break;
                 case "frames":
                     animation = new FrameBasedAnimationDriver(animationId, valueNode, endCallback, animationConfig);
                     break;
diff --git a/ReactWindows/ReactNative/ReactNative.csproj b/ReactWindows/ReactNative/ReactNative.csproj
@@ -118,6 +118,7 @@
     <Compile Include="Animated\AdditionAnimatedNode.cs" />
     <Compile Include="Animated\AnimatedNode.cs" />
     <Compile Include="Animated\AnimationDriver.cs" />
+    <Compile Include="Animated\DecayAnimationDriver.cs" />
     <Compile Include="Animated\FrameBasedAnimationDriver.cs" />
     <Compile Include="Animated\InterpolationAnimatedNode.cs" />
     <Compile Include="Animated\MultiplicationAnimatedNode.cs" />
