From b060c07db129aa8af48e744f5fe8fade38b9001f Mon Sep 17 00:00:00 2001
From: "Michael \"Z\" Goddard" <mzgoddard@gmail.com>
Date: Tue, 7 Nov 2017 17:18:23 -0500
Subject: [PATCH] Compare new setRotationCenter values after truncating to
 32bit

`Skin._rotationCenter` is a twgl vector or said another way a
Float32Array. JavaScript casts values stored in this array as 32 bit
floats instead of JavaScript's standard 64 bit floats. Comparing the
equality, like `setRotationCenter` does, of a 64 bit float against a
value stored in a 32 bit container will virtually always be false.
Truncating the new value into a 32 bit (losing precision) will give a
more useful comparison and remove a lot of current false positives.
---
 src/Skin.js | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/Skin.js b/src/Skin.js
index f54eddb..a92fdfe 100644
--- a/src/Skin.js
+++ b/src/Skin.js
@@ -4,6 +4,19 @@ const twgl = require('twgl.js');
 
 const RenderConstants = require('./RenderConstants');
 
+/**
+ * Truncate a number into what could be stored in a 32 bit floating point value.
+ * @param {number} num Number to truncate.
+ * @return {number} Truncated value.
+ */
+const toFloat32 = (function () {
+    const memory = new Float32Array(1);
+    return function (num) {
+        memory[0] = num;
+        return memory[0];
+    };
+}());
+
 class Skin extends EventEmitter {
     /**
      * Create a Skin, which stores and/or generates textures for use in rendering.
@@ -79,7 +92,11 @@ class Skin extends EventEmitter {
      */
     setRotationCenter (x, y) {
         const emptySkin = this.size[0] === 0 && this.size[1] === 0;
-        const changed = x !== this._rotationCenter[0] || y !== this._rotationCenter[1];
+        // Compare a 32 bit x and y value against the stored 32 bit center
+        // values.
+        const changed = (
+            toFloat32(x) !== this._rotationCenter[0] ||
+            toFloat32(y) !== this._rotationCenter[1]);
         if (!emptySkin && changed) {
             this._rotationCenter[0] = x;
             this._rotationCenter[1] = y;