From 6fbe42ba8f8f38ae25816cdf367dce44dc3b680a Mon Sep 17 00:00:00 2001
From: Justin Lin <caterpillar@openhome.cc>
Date: Mon, 13 May 2019 08:27:02 +0800
Subject: [PATCH] if a== 0 do_noting

---
 src/m_rotation.scad | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/m_rotation.scad b/src/m_rotation.scad
index 785bc421..22fbad82 100644
--- a/src/m_rotation.scad
+++ b/src/m_rotation.scad
@@ -78,4 +78,9 @@ function _xyz_rotation(a) =
     _m_zRotation(ang[2]) * _m_yRotation(ang[1]) * _m_xRotation(ang[0]);
 
 function m_rotation(a, v) = 
-    v == undef ? _xyz_rotation(a) : _q_rotation(a, v);
\ No newline at end of file
+    a == 0 ? [
+        [1, 0, 0, 0],
+        [0, 1, 0, 0],
+        [0, 0, 1, 0],
+        [0, 0, 0, 1]
+    ] : (v == undef ? _xyz_rotation(a) : _q_rotation(a, v));
\ No newline at end of file