Bugfix [#34283] armature bones losing their roll setting upon translation in

edit mode

My earlier fix for [#33974] (in r.54061) was causing some problems where
manually specified roll values on horizontal or angled bones were getting reset.
This could be nasty as you might not notice the changes for a while (especially
when using stick bones without axes displayed).

I've now put in place a hacky compromise solution which should catch both of
these situations nicely. For z-axis (i.e. vertical) movements, the r.54061 fix
is used, while for everything else (moving or just touch-n-go), the old setting
is used.

source/blender/editors/transform/transform_generics.c

@@ -809,6 +809,7 @@ static void recalcData_view3d(TransInfo *t)
 					if (td->extra) {
 						float vec[3], up_axis[3];
 						float qrot[4];
+						bool ztrans_hack = false;
 						
 						ebo = td->extra;
 						copy_v3_v3(up_axis, td->axismtx[2]);
@@ -823,7 +824,25 @@ static void recalcData_view3d(TransInfo *t)
 							mul_m3_v3(t->mat, up_axis);
 						}
 						
-						ebo->roll = ED_rollBoneToVector(ebo, up_axis, TRUE);
+						/* "ztrans_hack" is a hacky compromise fix for two bug reports
+						 *  - [#33974] : When extruding/translating bones vertically, 
+						 *               the roll of each bone in such vertical chains would
+						 *               flip between z-axis forward and z-axis backwards
+						 *  - [#34283] : For "normal" transforms, the original fix for [#33974]
+						 *               would cause manually-set roll values on horizontal and
+						 *               diagonal bones to constantly get reset to values the system
+						 *               deems "correct" (usually 180 degree flips of the manual version)
+						 */
+						if (t->mode == TFM_TRANSLATION) {
+							const float ZAXIS_REF[3] = {0.0f, 0.0f, 1.0f};
+							float tdelta[3];
+							
+							/* tdelta is the translation - enable this hack when it is z-axis movement */
+							normalize_v3_v3(tdelta, t->values);
+							ztrans_hack = compare_v3v3(tdelta, ZAXIS_REF, 0.1f);
+						}
+						
+						ebo->roll = ED_rollBoneToVector(ebo, up_axis, ztrans_hack);
 					}
 				}
 			}