MOD_curve: do not compute mesh when not needed.

This modifier only uses mesh to get vgroup, which is only needed in case
modified object is indeed a mesh! Building a mesh from curve here is not
only useless and time-consuming, it will also easily fail the assert
about same number of vertices!

Also, use MOD_get_vgroup() helper in modifier code itself and pass
reluting MDeformVert & index to BKE_curve's curve_deform_verts(),
this is simpler and avoids duplicating vgroup handling code.

Also fixes crash when used on lattice.

Related to T57972.

1 files changed, 2 insertions, 24 deletions

diff --git a/source/blender/blenkernel/intern/lattice.c b/source/blender/blenkernel/intern/lattice.c
index a04f32adece..0fa675639ea 100644
--- a/source/blender/blenkernel/intern/lattice.c
+++ b/source/blender/blenkernel/intern/lattice.c
@@ -704,14 +704,12 @@ static bool calc_curve_deform(Object *par, float co[3],
 }
 
 void curve_deform_verts(
-        Object *cuOb, Object *target, Mesh *mesh, float (*vertexCos)[3],
-        int numVerts, const char *vgroup, short defaxis)
+        Object *cuOb, Object *target, float (*vertexCos)[3],
+        int numVerts, MDeformVert *dvert, const int defgrp_index, short defaxis)
 {
 	Curve *cu;
 	int a;
 	CurveDeform cd;
-	MDeformVert *dvert = NULL;
-	int defgrp_index = -1;
 	const bool is_neg_axis = (defaxis > 2);
 
 	if (cuOb->type != OB_CURVE)
@@ -732,26 +730,6 @@ void curve_deform_verts(
 		cd.dmax[0] = cd.dmax[1] = cd.dmax[2] =  0.0f;
 	}
 
-	/* Check whether to use vertex groups (only possible if target is a Mesh or Lattice).
-	 * We want either a Mesh/Lattice with no derived data, or derived data with deformverts.
-	 */
-	if (vgroup && vgroup[0] && ELEM(target->type, OB_MESH, OB_LATTICE)) {
-		defgrp_index = defgroup_name_index(target, vgroup);
-
-		if (defgrp_index != -1) {
-			/* if there's derived data without deformverts, don't use vgroups */
-			if (mesh) {
-				dvert = CustomData_get_layer(&mesh->vdata, CD_MDEFORMVERT);
-			}
-			else if (target->type == OB_LATTICE) {
-				dvert = ((Lattice *)target->data)->dvert;
-			}
-			else {
-				dvert = ((Mesh *)target->data)->dvert;
-			}
-		}
-	}
-
 	if (dvert) {
 		MDeformVert *dvert_iter;
 		float vec[3];