Fix T38755: Crash when having cyclic dependency and curve deform

Issue was caused by undefined object update order and in some
cases NULL pointer will be de-referenced.

Added on-demand curve path calculation, just the same creepy call
of BKE_displist_make_curveTypes(). This violates DAG and might
end up in a difficult to troubleshoot race condition if there'll
be some issues with how dependencies are calculated in DAG, but
this is the easiest and safest way to solve the bug at this stage,

1 files changed, 19 insertions, 9 deletions

diff --git a/source/blender/blenkernel/intern/lattice.c b/source/blender/blenkernel/intern/lattice.c
index f7d394563ae..8330fefa0ae 100644
--- a/source/blender/blenkernel/intern/lattice.c
+++ b/source/blender/blenkernel/intern/lattice.c
@@ -64,6 +64,11 @@
 
 #include "BKE_deform.h"
 
+/* Workaround for cyclic depenndnecy with curves.
+ * In such case curve_cache might not be ready yet,
+ */
+#define CYCLIC_DEPENDENCY_WORKAROUND
+
 int BKE_lattice_index_from_uvw(Lattice *lt,
                                const int u, const int v, const int w)
 {
@@ -614,7 +619,7 @@ static bool where_on_path_deform(Object *ob, float ctime, float vec[4], float di
 /* co: local coord, result local too */
 /* returns quaternion for rotation, using cd->no_rot_axis */
 /* axis is using another define!!! */
-static bool calc_curve_deform(Object *par, float co[3],
+static bool calc_curve_deform(Scene *scene, Object *par, float co[3],
                               const short axis, CurveDeform *cd, float quat_r[4])
 {
 	Curve *cu = par->data;
@@ -624,7 +629,12 @@ static bool calc_curve_deform(Object *par, float co[3],
 
 	/* to be sure, mostly after file load */
 	if (ELEM(NULL, par->curve_cache, par->curve_cache->path)) {
-		return 0;  // happens on append and cyclic dependencies...
+#ifdef CYCLIC_DEPENDENCY_WORKAROUND
+		BKE_displist_make_curveTypes(scene, par, FALSE);
+#endif
+		if (par->curve_cache->path == NULL) {
+			return 0;  // happens on append and cyclic dependencies...
+		}
 	}
 	
 	/* options */
@@ -704,7 +714,7 @@ static bool calc_curve_deform(Object *par, float co[3],
 	return 0;
 }
 
-void curve_deform_verts(Object *cuOb, Object *target, DerivedMesh *dm, float (*vertexCos)[3],
+void curve_deform_verts(Scene *scene, Object *cuOb, Object *target, DerivedMesh *dm, float (*vertexCos)[3],
                         int numVerts, const char *vgroup, short defaxis)
 {
 	Curve *cu;
@@ -768,7 +778,7 @@ void curve_deform_verts(Object *cuOb, Object *target, DerivedMesh *dm, float (*v
 					if (weight > 0.0f) {
 						mul_m4_v3(cd.curvespace, vertexCos[a]);
 						copy_v3_v3(vec, vertexCos[a]);
-						calc_curve_deform(cuOb, vec, defaxis, &cd, NULL);
+						calc_curve_deform(scene, cuOb, vec, defaxis, &cd, NULL);
 						interp_v3_v3v3(vertexCos[a], vertexCos[a], vec, weight);
 						mul_m4_v3(cd.objectspace, vertexCos[a]);
 					}
@@ -796,7 +806,7 @@ void curve_deform_verts(Object *cuOb, Object *target, DerivedMesh *dm, float (*v
 					if (weight > 0.0f) {
 						/* already in 'cd.curvespace', prev for loop */
 						copy_v3_v3(vec, vertexCos[a]);
-						calc_curve_deform(cuOb, vec, defaxis, &cd, NULL);
+						calc_curve_deform(scene, cuOb, vec, defaxis, &cd, NULL);
 						interp_v3_v3v3(vertexCos[a], vertexCos[a], vec, weight);
 						mul_m4_v3(cd.objectspace, vertexCos[a]);
 					}
@@ -808,7 +818,7 @@ void curve_deform_verts(Object *cuOb, Object *target, DerivedMesh *dm, float (*v
 		if (cu->flag & CU_DEFORM_BOUNDS_OFF) {
 			for (a = 0; a < numVerts; a++) {
 				mul_m4_v3(cd.curvespace, vertexCos[a]);
-				calc_curve_deform(cuOb, vertexCos[a], defaxis, &cd, NULL);
+				calc_curve_deform(scene, cuOb, vertexCos[a], defaxis, &cd, NULL);
 				mul_m4_v3(cd.objectspace, vertexCos[a]);
 			}
 		}
@@ -823,7 +833,7 @@ void curve_deform_verts(Object *cuOb, Object *target, DerivedMesh *dm, float (*v
 	
 			for (a = 0; a < numVerts; a++) {
 				/* already in 'cd.curvespace', prev for loop */
-				calc_curve_deform(cuOb, vertexCos[a], defaxis, &cd, NULL);
+				calc_curve_deform(scene, cuOb, vertexCos[a], defaxis, &cd, NULL);
 				mul_m4_v3(cd.objectspace, vertexCos[a]);
 			}
 		}
@@ -833,7 +843,7 @@ void curve_deform_verts(Object *cuOb, Object *target, DerivedMesh *dm, float (*v
 /* input vec and orco = local coord in armature space */
 /* orco is original not-animated or deformed reference point */
 /* result written in vec and mat */
-void curve_deform_vector(Object *cuOb, Object *target,
+void curve_deform_vector(Scene *scene, Object *cuOb, Object *target,
                          float orco[3], float vec[3], float mat[3][3], int no_rot_axis)
 {
 	CurveDeform cd;
@@ -852,7 +862,7 @@ void curve_deform_vector(Object *cuOb, Object *target,
 
 	mul_m4_v3(cd.curvespace, vec);
 	
-	if (calc_curve_deform(cuOb, vec, target->trackflag, &cd, quat)) {
+	if (calc_curve_deform(scene, cuOb, vec, target->trackflag, &cd, quat)) {
 		float qmat[3][3];
 		
 		quat_to_mat3(qmat, quat);