quat_apply_track had incomplete comments

1 files changed, 11 insertions, 8 deletions

diff --git a/source/blender/blenlib/intern/math_rotation.c b/source/blender/blenlib/intern/math_rotation.c
index c4f12a5efc1..3b58fe88bf5 100644
--- a/source/blender/blenlib/intern/math_rotation.c
+++ b/source/blender/blenlib/intern/math_rotation.c
@@ -1539,21 +1539,24 @@ void quat_apply_track(float quat[4], short axis, short upflag)
 	                              {0.70710676908493, 0.0, 0.0, 0.70710676908493},  /* pos-z90 */ 
 	                              {0.70710676908493, 0.0, 0.70710676908493, 0.0}, /* neg-y90 */ 
 	                              {0.5, -0.5, -0.5, 0.5}, /* Quaternion((1,0,0), radians(-90)) * Quaternion((0,1,0), radians(-90)) */ 
-	                              {1, 0, 0, 0}};/* no rotation */ 
+	                              {-3.0908619663705394e-08, 0.70710676908493, 0.70710676908493, 3.0908619663705394e-08}}; /* no rotation */
 
 	mul_qt_qtqt(quat, quat, quat_track[axis]);
 
 	if(axis>2)
 		axis= axis-3;
 
-	/* 90d rotation when the second */
-	if(upflag != (2-axis)>>1) { // [0->1, 1->0, 2->0]
-		float q[4]= {0.70710676908493, 0, 0, 0};
+	/* there are 2 possible up-axis for each axis used, the 'quat_track' applies so the first
+	 * up axis is used X->Y, Y->X, Z->X, if this first up axis isn used then rotate 90d
+	 * the strange bit shift below just find the low axis {X:Y, Y:X, Z:X} */
+	if(upflag != (2-axis)>>1) {
+		float q[4]= {0.70710676908493, 0.0, 0.0, 0.0}; /* assign 90d rotation axis */
 		q[axis+1] = ((axis==1)) ? 0.70710676908493 : -0.70710676908493; /* flip non Y axis */
 		mul_qt_qtqt(quat, quat, q);
 	}
 }
 
+
 void vec_apply_track(float vec[3], short axis)
 {
 	float tvec[3];
@@ -1572,14 +1575,14 @@ void vec_apply_track(float vec[3], short axis)
 		/* vec[2]= tvec[2]; */ 
 		break;
 	case 2: /* pos-z */
-		vec[0]=  tvec[1];
-		vec[1]= -tvec[0];
+		/* vec[0]= tvec[0]; */
+		/* vec[1]= tvec[1]; */
 		// vec[2]=  0.0; */
 		break;
 	case 3: /* neg-x */
 		/* vec[0]=  0.0; */
-		vec[1]= -tvec[1];
-		vec[2]= -tvec[2];
+		vec[1]=  tvec[2];
+		vec[2]= -tvec[1];
 		break;
 	case 4: /* neg-y */
 		vec[0]= -tvec[2];