Fix precision issues and a bug in vec_roll_to_mat3_normalized.

When the input vector gets close to -Y, y and theta becomes totally
unreliable. It is thus necessary to compute the result in a different
way based on x and z. The code already had a special case, but:

- The threshold for using the special case was way too low.
- The special case was not precise enough to extend the threshold.
- The special case math had a sign error, resulting in a jump.

This adds tests for the computation precision and fixes the issues
by adjusting the threshold, and replacing the special case with one
based on a quadratic Taylor expansion of sqrt instead of linear.

Replacing the special case fixes the bug and results in a compatibility
break, requiring versioning for the roll of affected bones.

Differential Revision: https://developer.blender.org/D9551

1 files changed, 2 insertions, 2 deletions

diff --git a/source/blender/blenkernel/BKE_blender_version.h b/source/blender/blenkernel/BKE_blender_version.h
index 5ee86f9446e..899d21683e4 100644
--- a/source/blender/blenkernel/BKE_blender_version.h
+++ b/source/blender/blenkernel/BKE_blender_version.h
@@ -39,13 +39,13 @@ extern "C" {
 
 /* Blender file format version. */
 #define BLENDER_FILE_VERSION BLENDER_VERSION
-#define BLENDER_FILE_SUBVERSION 35
+#define BLENDER_FILE_SUBVERSION 36
 
 /* Minimum Blender version that supports reading file written with the current
  * version. Older Blender versions will test this and show a warning if the file
  * was written with too new a version. */
 #define BLENDER_FILE_MIN_VERSION 300
-#define BLENDER_FILE_MIN_SUBVERSION 26
+#define BLENDER_FILE_MIN_SUBVERSION 36
 
 /** User readable version string. */
 const char *BKE_blender_version_string(void);