Fix #138978: Modifier cage option not working when GPU subdivision is off

Need an equivalent of DRW_object_get_data_for_drawing for the cage mesh,
to ensure proper comparison between meshes.

Pull Request: https://projects.blender.org/blender/blender/pulls/138987

source/blender/blenkernel/BKE_mesh_wrapper.hh

@@ -48,3 +48,4 @@ void BKE_mesh_wrapper_vert_coords_copy_with_mat4(const Mesh *mesh,
                                                  const float mat[4][4]);
 
 Mesh *BKE_mesh_wrapper_ensure_subdivision(Mesh *mesh);
+const Mesh *BKE_mesh_wrapper_ensure_subdivision(const Mesh *mesh);

source/blender/blenkernel/intern/mesh_wrapper.cc

@@ -395,4 +395,11 @@ Mesh *BKE_mesh_wrapper_ensure_subdivision(Mesh *mesh)
   return result;
 }
 
+const Mesh *BKE_mesh_wrapper_ensure_subdivision(const Mesh *mesh)
+{
+  /* This modifies the mesh, but it's lazy initialization protected by mutex lock
+   * so still read-only access in a sense. */
+  return BKE_mesh_wrapper_ensure_subdivision(const_cast<Mesh *>(mesh));
+}
+
 /** \} */

source/blender/draw/intern/DRW_render.hh

@@ -217,6 +217,12 @@ template<typename T> T &DRW_object_get_data_for_drawing(const Object &object)
 
 template<> Mesh &DRW_object_get_data_for_drawing(const Object &object);
 
+/**
+ * Same as DRW_object_get_data_for_drawing, but for the editmesh cage,
+ * if it exists.
+ */
+const Mesh *DRW_object_get_editmesh_cage_for_drawing(const Object &object);
+
 /* Draw State. */
 
 /* -------------------------------------------------------------------- */

source/blender/draw/intern/draw_cache_extract_mesh_render_data.cc

@@ -24,6 +24,8 @@
 
 #include "ED_mesh.hh"
 
+#include "DRW_render.hh"
+
 #include "mesh_extractors/extract_mesh.hh"
 
 /* ---------------------------------------------------------------------- */
@@ -555,7 +557,7 @@ MeshRenderData mesh_render_data_create(Object &object,
 
   const Mesh *editmesh_orig = BKE_object_get_pre_modified_mesh(&object);
   if (is_editmode && editmesh_orig && editmesh_orig->runtime->edit_mesh) {
-    const Mesh *eval_cage = BKE_object_get_editmesh_eval_cage(&object);
+    const Mesh *eval_cage = DRW_object_get_editmesh_cage_for_drawing(object);
 
     mr.bm = editmesh_orig->runtime->edit_mesh->bm;
     mr.edit_bmesh = editmesh_orig->runtime->edit_mesh.get();

source/blender/draw/intern/draw_cache_impl_mesh.cc

@@ -1262,7 +1262,7 @@ void DRW_mesh_batch_cache_create_requested(TaskGraph &task_graph,
   bool do_cage = false;
   const Mesh *edit_data_mesh = nullptr;
   if (is_editmode) {
-    const Mesh *eval_cage = BKE_object_get_editmesh_eval_cage(&ob);
+    const Mesh *eval_cage = DRW_object_get_editmesh_cage_for_drawing(ob);
     if (eval_cage && eval_cage != &mesh) {
       /* Extract "cage" data separately when it exists and it's not just the same mesh as the
        * regular evaluated mesh. Otherwise edit data will be extracted from the final evaluated

source/blender/draw/intern/draw_context.cc

@@ -382,6 +382,21 @@ template<> Mesh &DRW_object_get_data_for_drawing(const Object &object)
   return *BKE_mesh_wrapper_ensure_subdivision(&mesh);
 }
 
+const Mesh *DRW_object_get_editmesh_cage_for_drawing(const Object &object)
+{
+  /* Same as DRW_object_get_data_for_drawing, but for the cage mesh. */
+  BLI_assert(object.type == OB_MESH);
+  const Mesh *cage_mesh = BKE_object_get_editmesh_eval_cage(&object);
+  if (cage_mesh == nullptr) {
+    return nullptr;
+  }
+
+  if (BKE_subsurf_modifier_has_gpu_subdiv(cage_mesh)) {
+    return cage_mesh;
+  }
+  return BKE_mesh_wrapper_ensure_subdivision(cage_mesh);
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */