From 3c9dc7ab87071c329cb2f15917111813bb998a6d Mon Sep 17 00:00:00 2001
From: pissang <bm2736892@gmail.com>
Date: Fri, 9 Jun 2017 14:06:06 +0800
Subject: [PATCH] Fix matrix decompose wrong when has negative scale component

---
 src/math/Matrix4.js | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/math/Matrix4.js b/src/math/Matrix4.js
index 044628d44..11b3f8c15 100644
--- a/src/math/Matrix4.js
+++ b/src/math/Matrix4.js
@@ -349,11 +349,15 @@ define(function(require) {
                 var sx = vec3.length(x);
                 var sy = vec3.length(y);
                 var sz = vec3.length(z);
+
+                // if determine is negative, we need to invert one scale
+                var det = this.determinant();
+                if (det < 0) {
+                    sx = -sx;
+                }
+
                 if (scale) {
-                    scale.x = sx;
-                    scale.y = sy;
-                    scale.z = sz;
-                    scale._dirty = true;
+                    scale.set(sx, sy, sz);
                 }
 
                 position.set(el[12], el[13], el[14]);