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, 12 insertions, 4 deletions

diff --git a/source/blender/modifiers/intern/MOD_curve.c b/source/blender/modifiers/intern/MOD_curve.c
index 73a541090e8..308cb79b74a 100644
--- a/source/blender/modifiers/intern/MOD_curve.c
+++ b/source/blender/modifiers/intern/MOD_curve.c
@@ -112,15 +112,23 @@ static void deformVerts(
         int numVerts)
 {
 	CurveModifierData *cmd = (CurveModifierData *) md;
-	Mesh *mesh_src = MOD_get_mesh_eval(ctx->object, NULL, mesh, NULL, false, false);
+	Mesh *mesh_src = NULL;
 
-	BLI_assert(mesh_src->totvert == numVerts);
+	if (ctx->object->type == OB_MESH) {
+		/* mesh_src is only needed for vgroups. */
+		mesh_src = MOD_get_mesh_eval(ctx->object, NULL, mesh, NULL, false, false);
+		BLI_assert(mesh_src->totvert == numVerts);
+	}
+
+	struct MDeformVert *dvert = NULL;
+	int defgrp_index = -1;
+	MOD_get_vgroup(ctx->object, mesh_src, cmd->name, &dvert, &defgrp_index);
 
 	/* silly that defaxis and curve_deform_verts are off by 1
 	 * but leave for now to save having to call do_versions */
-	curve_deform_verts(cmd->object, ctx->object, mesh_src, vertexCos, numVerts, cmd->name, cmd->defaxis - 1);
+	curve_deform_verts(cmd->object, ctx->object, vertexCos, numVerts, dvert, defgrp_index, cmd->defaxis - 1);
 
-	if (mesh_src != mesh) {
+	if (!ELEM(mesh_src, NULL, mesh)) {
 		BKE_id_free(NULL, mesh_src);
 	}
 }