Fix T38265: transferring vertex weights from an object with modifiers not working.

It was using the modified mesh for the vertex coordinates, and the unmodified mesh
for the vertex weights, which can't work and crashed in some cases, now it used the
modified mesh for both.

Perhaps an option should be added to indicate if you want to transfer from the
unmodified mesh or transfer to the modified mesh, but I think this fix makes it
works as intended when this was implemented.

1 files changed, 32 insertions, 9 deletions

diff --git a/source/blender/editors/object/object_vgroup.c b/source/blender/editors/object/object_vgroup.c
index b7cd3733e4d..04efacdb89d 100644
--- a/source/blender/editors/object/object_vgroup.c
+++ b/source/blender/editors/object/object_vgroup.c
@@ -328,6 +328,31 @@ bool ED_vgroup_parray_alloc(ID *id, MDeformVert ***dvert_arr, int *dvert_tot, co
 	return false;
 }
 
+static bool ed_vgroup_dm_parray_alloc(DerivedMesh *dm, MDeformVert ***dvert_arr, int *dvert_tot)
+{
+	*dvert_tot = 0;
+	*dvert_arr = NULL;
+
+	if (dm) {
+		MDeformVert *dvert = dm->getVertDataArray(dm, CD_MDEFORMVERT);
+
+		if (dvert) {
+			int i, totvert = dm->getNumVerts(dm);
+
+			*dvert_tot = totvert;
+			*dvert_arr = MEM_mallocN(sizeof(void *) * totvert, "vgroup parray from me");
+
+			for (i = 0; i < totvert; i++) {
+				(*dvert_arr)[i] = dvert + i;
+			}
+
+			return true;
+		}
+	}
+
+	return false;
+}
+
 /**
  * For use with tools that use ED_vgroup_parray_alloc with \a use_vert_sel == true.
  * This finds the unselected mirror deform verts and copys the weights to them from the selected.
@@ -863,7 +888,7 @@ static bool ed_vgroup_transfer_weight(Object *ob_dst, Object *ob_src, bDeformGro
                                       WT_Method method, WT_ReplaceMode replace_mode, wmOperator *op)
 {
 	bDeformGroup *dg_dst;
-	Mesh *me_dst, *me_src;
+	Mesh *me_dst;
 	DerivedMesh *dmesh_src;
 	BVHTreeFromMesh tree_mesh_vertices_src, tree_mesh_faces_src = {NULL};
 	MDeformVert **dv_array_src, **dv_array_dst, **dv_src, **dv_dst;
@@ -884,22 +909,20 @@ static bool ed_vgroup_transfer_weight(Object *ob_dst, Object *ob_src, bDeformGro
 	}
 
 	/* Get meshes.*/
-	dmesh_src = mesh_get_derived_deform(scene, ob_src, CD_MASK_BAREMESH);
+	dmesh_src = mesh_get_derived_final(scene, ob_src, CD_MASK_BAREMESH|CD_MASK_MDEFORMVERT);
 	me_dst = ob_dst->data;
-	me_src = ob_src->data;
 
-	/* Sanity check.*/
-	if (!me_src->dvert) {
+	/* Get vertex group array from source mesh */
+	if (!ed_vgroup_dm_parray_alloc(dmesh_src, &dv_array_src, &dv_tot_src)) {
 		BKE_report(op->reports, RPT_ERROR, "Transfer failed (source mesh does not have any vertex groups)");
 		return false;
 	}
 
 	/* Create data in memory when nothing there.*/
-	if (!me_dst->dvert) ED_vgroup_data_create(ob_dst->data);
+	if (!me_dst->dvert) ED_vgroup_data_create(&me_dst->id);
 
-	/* Get vertex group arrays.*/
-	ED_vgroup_parray_alloc(ob_src->data, &dv_array_src, &dv_tot_src, false);
-	ED_vgroup_parray_alloc(ob_dst->data, &dv_array_dst, &dv_tot_dst, use_vert_sel);
+	/* Get vertex group for destination mesh */
+	ED_vgroup_parray_alloc(&me_dst->id, &dv_array_dst, &dv_tot_dst, use_vert_sel);
 
 	/* Get indexes of vertex groups.*/
 	index_src = BLI_findindex(&ob_src->defbase, dg_src);