From 77b6e2653835af61b186903eae45d67f35351ade Mon Sep 17 00:00:00 2001
From: Martin Sherburn <mns@oculus.com>
Date: Tue, 8 Oct 2019 05:54:08 -0700
Subject: [PATCH] Fix TimingAnimation rounding error issue

Summary:
This fixes a bug where the frames array can contain a duplicate entry at the end.
For example, suppose the duration is 1000.0 then it would create an array with the following:

```
[ 0,
  0.0010119824303159884,
  0.00391003997863186,
  0.00851330482578147,
  0.01466951184383165,
  0.022249135687575607,
  0.03114100006836614,
  0.041248932923769244,
  0.05248918022066495,
  0.06478838042267626,
  0.07808196049642172,
  0.09231285402599128,
  0.1074304693764467,
  0.12338985513375342,
  0.14015102395653428,
  0.15767840628626964,
  0.17594041329987542,
  0.1949090949486824,
  0.21455988464815853,
  0.23487142789035506,
  0.25582549864491233,
  0.27740701626433145,
  0.2996041891505173,
  0.3224088345090182,
  0.34581696665965683,
  0.36982983491413496,
  0.394455794287552,
  0.4197139228812336,
  0.44564199741037275,
  0.4723190090623474,
  0.5000000572130084,
  0.5276809909376533,
  0.5543580025896278,
  0.5802860771187669,
  0.6055442057124484,
  0.6301701650858652,
  0.6541830333403433,
  0.6775911654909819,
  0.7003958108494828,
  0.7225929837356684,
  0.7441745013550876,
  0.7651285721096447,
  0.785440115351841,
  0.8050909050513173,
  0.8240595867001241,
  0.84232159371373,
  0.8598489760434653,
  0.876610144866246,
  0.8925695306235529,
  0.9076871459740083,
  0.9219180395035779,
  0.9352116195773232,
  0.9475108197793346,
  0.9587510670762303,
  0.9688589999316335,
  0.9777508643124241,
  0.9853304881561681,
  0.9914866951742183,
  0.996089960021368,
  0.9989880175696839,
  1,
  1 ]
```

With this change, it now generates the following array:

```
[ 0,
  0.0010119824303159884,
  0.00391003997863186,
  0.00851330482578147,
  0.01466951184383165,
  0.022249135687575607,
  0.03114100006836614,
  0.041248932923769244,
  0.05248918022066495,
  0.06478838042267626,
  0.07808196049642172,
  0.09231285402599128,
  0.1074304693764467,
  0.12338985513375342,
  0.14015102395653428,
  0.15767840628626964,
  0.17594041329987542,
  0.1949090949486824,
  0.21455988464815853,
  0.23487142789035506,
  0.25582549864491233,
  0.27740701626433145,
  0.2996041891505173,
  0.3224088345090182,
  0.34581696665965683,
  0.36982983491413496,
  0.394455794287552,
  0.4197139228812336,
  0.44564199741037275,
  0.4723190090623474,
  0.5000000572130084,
  0.5276809909376533,
  0.5543580025896278,
  0.5802860771187669,
  0.6055442057124484,
  0.6301701650858652,
  0.6541830333403433,
  0.6775911654909819,
  0.7003958108494828,
  0.7225929837356684,
  0.7441745013550876,
  0.7651285721096447,
  0.785440115351841,
  0.8050909050513173,
  0.8240595867001241,
  0.84232159371373,
  0.8598489760434653,
  0.876610144866246,
  0.8925695306235529,
  0.9076871459740083,
  0.9219180395035779,
  0.9352116195773232,
  0.9475108197793346,
  0.9587510670762303,
  0.9688589999316335,
  0.9777508643124241,
  0.9853304881561681,
  0.9914866951742183,
  0.996089960021368,
  0.9989880175696839,
  1 ]
```

Note that the duplicate 1 at the end is now gone. This is because previously when it accumulated dt for 60 frames. dt wasn't quite exactly 1000, it was instead 999.9999999999999 and so didn't break out of the loop when it should have. This adds a tolerance so that it does break out of the loop.

Reviewed By: sahrens

Differential Revision: D17738602

fbshipit-source-id: deba5d5a08ae842e2a9e2b75f2e25e14f3700518
---
 .../src/__tests__/TimingAnimation-test.js     | 24 +++++++++++++++++++
 .../src/animations/TimingAnimation.js         |  6 ++---
 2 files changed, 27 insertions(+), 3 deletions(-)
 create mode 100644 Libraries/Animated/src/__tests__/TimingAnimation-test.js

diff --git a/Libraries/Animated/src/__tests__/TimingAnimation-test.js b/Libraries/Animated/src/__tests__/TimingAnimation-test.js
new file mode 100644
index 00000000000000..5e53f6b41c8341
--- /dev/null
+++ b/Libraries/Animated/src/__tests__/TimingAnimation-test.js
@@ -0,0 +1,24 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ * @emails oncall+react_native
+ */
+
+'use strict';
+
+const TimingAnimation = require('../animations/TimingAnimation');
+
+describe('Timing Animation', () => {
+  it('should return array of 61 items', () => {
+    const timingAnim = new TimingAnimation({duration: 1000});
+    const config = timingAnim.__getNativeAnimationConfig();
+
+    expect(config.frames.length).toBe(61);
+    expect(config.frames[60]).toBe(1);
+    expect(config.frames[59]).toBeLessThan(1);
+  });
+});
diff --git a/Libraries/Animated/src/animations/TimingAnimation.js b/Libraries/Animated/src/animations/TimingAnimation.js
index b73794f1333e44..d185869c9bf0a7 100644
--- a/Libraries/Animated/src/animations/TimingAnimation.js
+++ b/Libraries/Animated/src/animations/TimingAnimation.js
@@ -66,10 +66,10 @@ class TimingAnimation extends Animation {
   __getNativeAnimationConfig(): any {
     const frameDuration = 1000.0 / 60.0;
     const frames = [];
-    for (let dt = 0.0; dt < this._duration; dt += frameDuration) {
-      frames.push(this._easing(dt / this._duration));
+    const numFrames = Math.round(this._duration / frameDuration);
+    for (let frame = 0; frame <= numFrames; frame++) {
+      frames.push(this._easing(frame / numFrames));
     }
-    frames.push(this._easing(1));
     return {
       type: 'frames',
       frames,