Fix T42256: Translation operator moves Child-Of constrained objects in wrong space when only using parent's rotation and parent is rotated.

Just do not use crazyspace correction with childof constraints in this case.

Note this is only a very partial fix (partial use of parent loc on some axes
is still broken in transform), a real fix would probably require a full rewrite
of constraints handling in transform code (a mere static correction matrix
just cannot work in all possible cases, we'd need a full dynamic correction system here).
Anyway, transform code as a whole is horrible. :/

2 files changed, 12 insertions, 2 deletions

diff --git a/source/blender/blenkernel/intern/constraint.c b/source/blender/blenkernel/intern/constraint.c
index 97515244422..8a5d313e3fb 100644
--- a/source/blender/blenkernel/intern/constraint.c
+++ b/source/blender/blenkernel/intern/constraint.c
@@ -185,6 +185,10 @@ void BKE_constraints_clear_evalob(bConstraintOb *cob)
 	
 	/* calculate delta of constraints evaluation */
 	invert_m4_m4(imat, cob->startmat);
+	/* XXX This would seem to be in wrong order. However, it does not work in 'right' order - would be nice to
+	 *     understand why premul is needed here instead of usual postmul?
+	 *     In any case, we **do not get a delta** here (e.g. startmat & matrix having same location, still gives
+	 *     a 'delta' with non-null translation component :/ ).*/
 	mul_m4_m4m4(delta, cob->matrix, imat);
 	
 	/* copy matrices back to source */
diff --git a/source/blender/editors/transform/transform_conversions.c b/source/blender/editors/transform/transform_conversions.c
index e27dafca9af..3b92e018d49 100644
--- a/source/blender/editors/transform/transform_conversions.c
+++ b/source/blender/editors/transform/transform_conversions.c
@@ -4771,7 +4771,6 @@ static bool constraints_list_needinv(TransInfo *t, ListBase *list)
 				/* (affirmative) returns for specific constraints here... */
 				/* constraints that require this regardless  */
 				if (ELEM(con->type,
-				         CONSTRAINT_TYPE_CHILDOF,
 				         CONSTRAINT_TYPE_FOLLOWPATH,
 				         CONSTRAINT_TYPE_CLAMPTO,
 				         CONSTRAINT_TYPE_OBJECTSOLVER,
@@ -4781,7 +4780,14 @@ static bool constraints_list_needinv(TransInfo *t, ListBase *list)
 				}
 				
 				/* constraints that require this only under special conditions */
-				if (con->type == CONSTRAINT_TYPE_ROTLIKE) {
+				if (con->type == CONSTRAINT_TYPE_CHILDOF) {
+					/* ChildOf constraint only works when using all location components, see T42256. */
+					bChildOfConstraint *data = (bChildOfConstraint *)con->data;
+					
+					if ((data->flag & CHILDOF_LOCX) && (data->flag & CHILDOF_LOCY) && (data->flag & CHILDOF_LOCZ))
+						return true;
+				}
+				else if (con->type == CONSTRAINT_TYPE_ROTLIKE) {
 					/* CopyRot constraint only does this when rotating, and offset is on */
 					bRotateLikeConstraint *data = (bRotateLikeConstraint *)con->data;