[Bf-blender-cvs] [ac2ebf9c54a] master: Fix T53455: Object disappear w/ TrackTo constraint

[Campbell Barton]

Commit: ac2ebf9c54a9081662ab17f04240c00d9e5ac799
Author: Campbell Barton
Date:   Thu Jan 11 10:57:30 2018 +1100
Branches: master
https://developer.blender.org/rBac2ebf9c54a9081662ab17f04240c00d9e5ac799

Fix T53455: Object disappear w/ TrackTo constraint

Regression caused by own commit 16fbb47c886,
this is really an edge case though since calling normalize twice fixes.

===================================================================

M	source/blender/blenkernel/intern/constraint.c

===================================================================

diff --git a/source/blender/blenkernel/intern/constraint.c b/source/blender/blenkernel/intern/constraint.c
index a5d0df88198..c77cac7bcbd 100644
--- a/source/blender/blenkernel/intern/constraint.c
+++ b/source/blender/blenkernel/intern/constraint.c
@@ -1018,8 +1018,11 @@ static void vectomat(const float vec[3], const float target_up[3], short axis, s
 		u[2] = 1;
 	}
 
+	/* note: even though 'n' is normalized, don't use 'project_v3_v3v3_normalized' below
+	 * because precision issues cause a problem in near degenerate states, see: T53455. */
+
 	/* project the up vector onto the plane specified by n */
-	project_v3_v3v3_normalized(proj, u, n); /* first u onto n... */
+	project_v3_v3v3(proj, u, n); /* first u onto n... */
 	sub_v3_v3v3(proj, u, proj); /* then onto the plane */
 	/* proj specifies the transformation of the up axis */