Fix T62271: Particles with multires crash on sculpt

In fact, any modifier on top of multires would lead to crash.
Was missing pointer update.

Basically, bring the control flow closer to 2.7.

3 files changed, 20 insertions, 1 deletions

diff --git a/source/blender/blenkernel/BKE_paint.h b/source/blender/blenkernel/BKE_paint.h
index 25fb55011b2..cc445413f61 100644
--- a/source/blender/blenkernel/BKE_paint.h
+++ b/source/blender/blenkernel/BKE_paint.h
@@ -56,6 +56,7 @@ struct UnifiedPaintSettings;
 struct ViewLayer;
 struct bContext;
 struct bToolRef;
+struct SubdivCCG;
 
 enum eOverlayFlags;
 
@@ -287,6 +288,8 @@ void BKE_sculpt_toolsettings_data_ensure(struct Scene *scene);
 
 struct PBVH *BKE_sculpt_object_pbvh_ensure(struct Depsgraph *depsgraph, struct Object *ob);
 
+void BKE_sculpt_bvh_update_from_ccg(struct PBVH *pbvh, struct SubdivCCG *subdiv_ccg);
+
 enum {
 	SCULPT_MASK_LAYER_CALC_VERT = (1 << 0),
 	SCULPT_MASK_LAYER_CALC_LOOP = (1 << 1),
diff --git a/source/blender/blenkernel/intern/paint.c b/source/blender/blenkernel/intern/paint.c
index b3999e61216..be0d176dddc 100644
--- a/source/blender/blenkernel/intern/paint.c
+++ b/source/blender/blenkernel/intern/paint.c
@@ -1381,7 +1381,16 @@ PBVH *BKE_sculpt_object_pbvh_ensure(Depsgraph *depsgraph, Object *ob)
 	}
 	PBVH *pbvh = ob->sculpt->pbvh;
 	if (pbvh != NULL) {
-		/* Nothing to do, PBVH is already up to date. */
+		/* NOTE: It is possible that grids were re-allocated due to modifier
+		 * stack. Need to update those pointers. */
+		if (BKE_pbvh_type(pbvh) == PBVH_GRIDS) {
+			Object *object_eval = DEG_get_evaluated_object(depsgraph, ob);
+			Mesh *mesh_eval = object_eval->data;
+			SubdivCCG *subdiv_ccg = mesh_eval->runtime.subdiv_ccg;
+			if (subdiv_ccg != NULL) {
+				BKE_sculpt_bvh_update_from_ccg(pbvh, subdiv_ccg);
+			}
+		}
 		return pbvh;
 	}
 
@@ -1405,3 +1414,9 @@ PBVH *BKE_sculpt_object_pbvh_ensure(Depsgraph *depsgraph, Object *ob)
 	ob->sculpt->pbvh = pbvh;
 	return pbvh;
 }
+
+void BKE_sculpt_bvh_update_from_ccg(PBVH *pbvh, SubdivCCG *subdiv_ccg)
+{
+	BKE_pbvh_grids_update(pbvh, subdiv_ccg->grids, (void **)subdiv_ccg->grid_faces,
+	                      subdiv_ccg->grid_flag_mats, subdiv_ccg->grid_hidden);
+}
diff --git a/source/blender/draw/modes/sculpt_mode.c b/source/blender/draw/modes/sculpt_mode.c
index 1a525f24349..a0ae5d0754a 100644
--- a/source/blender/draw/modes/sculpt_mode.c
+++ b/source/blender/draw/modes/sculpt_mode.c
@@ -164,6 +164,7 @@ static void sculpt_update_pbvh_normals(Object *object)
 	if (pbvh == NULL || subdiv_ccg == NULL) {
 		return;
 	}
+	BKE_sculpt_bvh_update_from_ccg(pbvh, subdiv_ccg);
 	struct CCGFace **faces;
 	int num_faces;
 	BKE_pbvh_get_grid_updates(pbvh, 1, (void ***)&faces, &num_faces);