Fix T96283: last disabled subsurf is used for GPU subdivision

When more than one, consecutive, subdivision modifier is used on a Mesh,
the last subsurf modifier is used for GPU subdivision even though it
might be disabled. This is because retrieving the last subsurf modifier
in the draw code did not check whether the modifier was disabled or not.

To fix this, the session UUID of the modifier which delegated evaluation
to the GPU code is cached and used in the draw to select the right subsurf
modifier.

Differential Revision: https://developer.blender.org/D14488

source/blender/draw/intern/draw_cache_impl_subdivision.cc

@@ -1898,7 +1898,8 @@ static bool draw_subdiv_create_requested_buffers(const Scene *scene,
                                                  const bool /*use_hide*/,
                                                  OpenSubdiv_EvaluatorCache *evaluator_cache)
 {
-  SubsurfModifierData *smd = BKE_object_get_last_subsurf_modifier(ob);
+  SubsurfModifierData *smd = reinterpret_cast<SubsurfModifierData *>(
+       BKE_modifiers_findby_session_uuid(ob, &mesh->runtime.subsurf_session_uuid));
   BLI_assert(smd);
 
   const bool is_final_render = DRW_state_is_scene_render();

source/blender/makesdna/DNA_mesh_types.h

@@ -10,6 +10,7 @@
 #include "DNA_ID.h"
 #include "DNA_customdata_types.h"
 #include "DNA_defs.h"
+#include "DNA_session_uuid_types.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -120,11 +121,12 @@ typedef struct Mesh_Runtime {
    */
   char wrapper_type_finalize;
 
-  int subsurf_resolution;
   /**
    * Settings for lazily evaluating the subdivision on the CPU if needed. These are
    * set in the modifier when GPU subdivision can be performed.
    */
+  SessionUUID subsurf_session_uuid;
+  int subsurf_resolution;
   char subsurf_apply_render;
   char subsurf_use_optimal_display;
 

source/blender/modifiers/intern/MOD_subsurf.c

@@ -205,6 +205,7 @@ static void subdiv_cache_cpu_evaluation_settings(const ModifierEvalContext *ctx,
   me->runtime.subsurf_apply_render = (ctx->flag & MOD_APPLY_RENDER) != 0;
   me->runtime.subsurf_resolution = mesh_settings.resolution;
   me->runtime.subsurf_use_optimal_display = mesh_settings.use_optimal_display;
+  me->runtime.subsurf_session_uuid = smd->modifier.session_uuid;
 }
 
 /* Modifier itself. */