Fix T67888: Incorrect Wireframe After Applying SubSurf/MultiRes

Show control edges stores the control edges in the mesh which is
picked up by the draw manager. When applyng a subsurf (or multires) we
don't want that data present in the base mesh. Any rebuilding of the mesh
would overwrite the data anyway.

This patch introduces a new flag for applying modifiers
that can be checked to ignore storing display specific data in
the base mesh.

Reviewed By: Brecht van Lommel

Differential Revision: https://developer.blender.org/D7163

source/blender/blenkernel/BKE_modifier.h

@@ -125,6 +125,11 @@ typedef enum ModifierApplyFlag {
   /** Ignore scene simplification flag and use subdivisions
    * level set in multires modifier. */
   MOD_APPLY_IGNORE_SIMPLIFY = 1 << 3,
+  /** The effect of this modifier will be applied to the base mesh
+   * The modifier itself will be removed from the modifier stack.
+   * This flag can be checked to ignore rendering display data to the mesh.
+   * See `OBJECT_OT_modifier_apply` operator. */
+  MOD_APPLY_TO_BASE_MESH = 1 << 4,
 } ModifierApplyFlag;
 
 typedef struct ModifierUpdateDepsgraphContext {

source/blender/blenkernel/BKE_multires.h

@@ -197,7 +197,8 @@ void BKE_multires_subdiv_mesh_settings_init(struct SubdivToMeshSettings *mesh_se
                                             const struct Object *object,
                                             const struct MultiresModifierData *mmd,
                                             const bool use_render_params,
-                                            const bool ignore_simplify);
+                                            const bool ignore_simplify,
+                                            const bool ignore_control_edges);
 
 /* General helpers. */
 

source/blender/blenkernel/intern/mesh_convert.c

@@ -1304,7 +1304,7 @@ Mesh *BKE_mesh_create_derived_for_modifier(struct Depsgraph *depsgraph,
   const ModifierTypeInfo *mti = modifierType_getInfo(md_eval->type);
   Mesh *result;
   KeyBlock *kb;
-  ModifierEvalContext mectx = {depsgraph, ob_eval, 0};
+  ModifierEvalContext mectx = {depsgraph, ob_eval, MOD_APPLY_TO_BASE_MESH};
 
   if (!(md_eval->mode & eModifierMode_Realtime)) {
     return NULL;

source/blender/blenkernel/intern/multires_subdiv.c

@@ -50,9 +50,11 @@ void BKE_multires_subdiv_mesh_settings_init(SubdivToMeshSettings *mesh_settings,
                                             const Object *object,
                                             const MultiresModifierData *mmd,
                                             const bool use_render_params,
-                                            const bool ignore_simplify)
+                                            const bool ignore_simplify,
+                                            const bool ignore_control_edges)
 {
   const int level = multires_get_level(scene, object, mmd, use_render_params, ignore_simplify);
   mesh_settings->resolution = (1 << level) + 1;
-  mesh_settings->use_optimal_display = (mmd->flags & eMultiresModifierFlag_ControlEdges);
+  mesh_settings->use_optimal_display = (mmd->flags & eMultiresModifierFlag_ControlEdges) &&
+                                       !ignore_control_edges;
 }

source/blender/modifiers/intern/MOD_multires.c

@@ -119,11 +119,17 @@ static Mesh *multires_as_mesh(MultiresModifierData *mmd,
   Mesh *result = mesh;
   const bool use_render_params = (ctx->flag & MOD_APPLY_RENDER);
   const bool ignore_simplify = (ctx->flag & MOD_APPLY_IGNORE_SIMPLIFY);
+  const bool ignore_control_edges = (ctx->flag & MOD_APPLY_TO_BASE_MESH);
   const Scene *scene = DEG_get_evaluated_scene(ctx->depsgraph);
   Object *object = ctx->object;
   SubdivToMeshSettings mesh_settings;
-  BKE_multires_subdiv_mesh_settings_init(
-      &mesh_settings, scene, object, mmd, use_render_params, ignore_simplify);
+  BKE_multires_subdiv_mesh_settings_init(&mesh_settings,
+                                         scene,
+                                         object,
+                                         mmd,
+                                         use_render_params,
+                                         ignore_simplify,
+                                         ignore_control_edges);
   if (mesh_settings.resolution < 3) {
     return result;
   }

source/blender/modifiers/intern/MOD_subsurf.c

@@ -148,7 +148,8 @@ static void subdiv_mesh_settings_init(SubdivToMeshSettings *settings,
 {
   const int level = subdiv_levels_for_modifier_get(smd, ctx);
   settings->resolution = (1 << level) + 1;
-  settings->use_optimal_display = (smd->flags & eSubsurfModifierFlag_ControlEdges);
+  settings->use_optimal_display = (smd->flags & eSubsurfModifierFlag_ControlEdges) &&
+                                  !(ctx->flag & MOD_APPLY_TO_BASE_MESH);
 }
 
 static Mesh *subdiv_as_mesh(SubsurfModifierData *smd,