Disable GPU subdivision if autosmooth or split normals are used

These features are complicated to support on GPU and hardly compatible
with subdivision in the first place. In the future, with T68891 and
T68893, subdivision and custom smooth shading will be separate workflows.
For now, and to better prepare for this future (although long term
plan), we should discourage workflows mixing subdivision and custom
smooth normals, and as such, this disables GPU subdivision when
autosmoothing or custom split normals are used.

This also adds a message in the modifier's UI to indicate that GPU
subdivision will be disabled if autosmooth or custom split normals are
used on the mesh.

Differential Revision: https://developer.blender.org/D14194

1 files changed, 10 insertions, 4 deletions

diff --git a/source/blender/modifiers/intern/MOD_subsurf.c b/source/blender/modifiers/intern/MOD_subsurf.c
index a8c6687193b..2006ca1b1b7 100644
--- a/source/blender/modifiers/intern/MOD_subsurf.c
+++ b/source/blender/modifiers/intern/MOD_subsurf.c
@@ -250,7 +250,8 @@ static Mesh *modifyMesh(ModifierData *md, const ModifierEvalContext *ctx, Mesh *
      * assigned at this stage of modifier stack evaluation. */
     const bool is_editmode = (mesh->edit_mesh != NULL);
     const int required_mode = BKE_subsurf_modifier_eval_required_mode(is_render_mode, is_editmode);
-    if (BKE_subsurf_modifier_can_do_gpu_subdiv_ex(scene, ctx->object, smd, required_mode, false)) {
+    if (BKE_subsurf_modifier_can_do_gpu_subdiv_ex(
+            scene, ctx->object, mesh, smd, required_mode, false)) {
       subdiv_cache_cpu_evaluation_settings(ctx, mesh, smd);
       return result;
     }
@@ -262,9 +263,7 @@ static Mesh *modifyMesh(ModifierData *md, const ModifierEvalContext *ctx, Mesh *
     /* Happens on bad topology, but also on empty input mesh. */
     return result;
   }
-  const bool use_clnors = (smd->flags & eSubsurfModifierFlag_UseCustomNormals) &&
-                          (mesh->flag & ME_AUTOSMOOTH) &&
-                          CustomData_has_layer(&mesh->ldata, CD_CUSTOMLOOPNORMAL);
+  const bool use_clnors = BKE_subsurf_modifier_use_custom_loop_normals(smd, mesh);
   if (use_clnors) {
     /* If custom normals are present and the option is turned on calculate the split
      * normals and clear flag so the normals get interpolated to the result mesh. */
@@ -428,6 +427,13 @@ static void panel_draw(const bContext *C, Panel *panel)
 
   uiItemR(layout, ptr, "show_only_control_edges", 0, NULL, ICON_NONE);
 
+  SubsurfModifierData *smd = ptr->data;
+  Object *ob = ob_ptr.data;
+  Mesh *mesh = ob->data;
+  if (BKE_subsurf_modifier_force_disable_gpu_evaluation_for_mesh(smd, mesh)) {
+    uiItemL(layout, "Autosmooth or custom normals detected, disabling GPU subdivision", ICON_INFO);
+  }
+
   modifier_panel_end(layout, ptr);
 }