Bugfix #8736: Follow Path constraints does not work for Bones

This appears to be a long-standing bug, and it only affected the Follow-Path constraint as it was the only one which was dependant on time-based changes. An oversight in the depsgraph code meant that Follow-Path constraints on armature bones were not evaluated, unless there was an Action or some NLA-Strips for that armature. 

I've added a new flag to pose->flag (POSE_CONSTRAINTS_TIMEDEPEND) which only gets set/cleared by update_pose_constraint_flags. This flag indicates that the depsgraph needs to do an update for such cases, and will require going in/out of EditMode to set this for old files. 
It's been implemented as such to avoid having costly searches when trying to run animations realtime (as is done for modifiers).

2 files changed, 24 insertions, 6 deletions

diff --git a/source/blender/blenkernel/intern/action.c b/source/blender/blenkernel/intern/action.c
index 3b4de305545..21a15fd5a4a 100644
--- a/source/blender/blenkernel/intern/action.c
+++ b/source/blender/blenkernel/intern/action.c
@@ -353,7 +353,9 @@ static void copy_pose_channel_data(bPoseChannel *pchan, const bPoseChannel *chan
 	}
 }
 
-/* checks for IK constraint, can do more constraints flags later */
+/* checks for IK constraint, and also for Follow-Path constraint.
+ * can do more constraints flags later 
+ */
 /* pose should be entirely OK */
 void update_pose_constraint_flags(bPose *pose)
 {
@@ -361,13 +363,15 @@ void update_pose_constraint_flags(bPose *pose)
 	bConstraint *con;
 	
 	/* clear */
-	for (pchan = pose->chanbase.first; pchan; pchan=pchan->next) {
+	for (pchan= pose->chanbase.first; pchan; pchan= pchan->next) {
 		pchan->constflag= 0;
 	}
+	pose->flag &= ~POSE_CONSTRAINTS_TIMEDEPEND;
+	
 	/* detect */
-	for (pchan = pose->chanbase.first; pchan; pchan=pchan->next) {
-		for(con= pchan->constraints.first; con; con= con->next) {
-			if(con->type==CONSTRAINT_TYPE_KINEMATIC) {
+	for (pchan= pose->chanbase.first; pchan; pchan=pchan->next) {
+		for (con= pchan->constraints.first; con; con= con->next) {
+			if (con->type==CONSTRAINT_TYPE_KINEMATIC) {
 				bKinematicConstraint *data = (bKinematicConstraint*)con->data;
 				
 				pchan->constflag |= PCHAN_HAS_IK;
@@ -390,7 +394,20 @@ void update_pose_constraint_flags(bPose *pose)
 					}
 				}
 			}
-			else pchan->constflag |= PCHAN_HAS_CONST;
+			else if (con->type == CONSTRAINT_TYPE_FOLLOWPATH) {
+				bFollowPathConstraint *data= (bFollowPathConstraint *)con->data;
+				
+				/* for drawing constraint colors when color set allows this */
+				pchan->constflag |= PCHAN_HAS_CONST;
+				
+				/* if we have a valid target, make sure that this will get updated on frame-change
+				 * (needed for when there is no anim-data for this pose)
+				 */
+				if ((data->tar) && (data->tar->type==OB_CURVE))
+					pose->flag |= POSE_CONSTRAINTS_TIMEDEPEND;
+			}
+			else 
+				pchan->constflag |= PCHAN_HAS_CONST;
 		}
 	}
 }
diff --git a/source/blender/blenkernel/intern/depsgraph.c b/source/blender/blenkernel/intern/depsgraph.c
index 32927b6058c..5f95ce61aca 100644
--- a/source/blender/blenkernel/intern/depsgraph.c
+++ b/source/blender/blenkernel/intern/depsgraph.c
@@ -1848,6 +1848,7 @@ static void dag_object_time_update_flags(Object *ob)
 	}
 	else if(modifiers_isSoftbodyEnabled(ob)) ob->recalc |= OB_RECALC_DATA;
 	else if(object_modifiers_use_time(ob)) ob->recalc |= OB_RECALC_DATA;
+	else if((ob->pose) && (ob->pose->flag & POSE_CONSTRAINTS_TIMEDEPEND)) ob->recalc |= OB_RECALC_DATA;
 	else {
 		Mesh *me;
 		Curve *cu;