Fix T98813: crash with GPU subdiv in edit mode and instanced geometry

Instancing with geometry nodes uses just the evaluated Mesh, and ignores the
Object that it came from. That meant that it would try to look up the subsurf
modifier on the instancer object which does not have the subsurf modifier.

Instead of storing a session UUID and looking up the modifier data, store a
point to the subsurf modifier runtime data. Unlike the modifier data, this
runtime data is preserved across depsgraph CoW. It must be for the subdiv
descriptor contained in it to stay valid along with the draw cache.

As a bonus, this moves various Mesh_Runtime variables into the subsurf runtime
data, reducing memory usage for meshes not using subdivision surfaces.

Also fixes T98693, issues with subdivision level >= 8 due to integer overflow.

Differential Revision: https://developer.blender.org/D15184

2 files changed, 6 insertions, 20 deletions

diff --git a/source/blender/makesdna/DNA_mesh_types.h b/source/blender/makesdna/DNA_mesh_types.h
index a66badb4a68..2eca84959b8 100644
--- a/source/blender/makesdna/DNA_mesh_types.h
+++ b/source/blender/makesdna/DNA_mesh_types.h
@@ -32,6 +32,7 @@ struct MVert;
 struct Material;
 struct Mesh;
 struct SubdivCCG;
+struct SubsurfRuntimeData;
 
 #
 #
@@ -123,26 +124,18 @@ typedef struct Mesh_Runtime {
 
   /**
    * Settings for lazily evaluating the subdivision on the CPU if needed. These are
-   * set in the modifier when GPU subdivision can be performed.
+   * set in the modifier when GPU subdivision can be performed, and owned by the by
+   * the modifier in the object.
    */
-  SessionUUID subsurf_session_uuid;
-  char subsurf_resolution;
-  char subsurf_do_loop_normals;
-  char subsurf_apply_render;
-  char subsurf_use_optimal_display;
-
-  /* Cached from the draw code for stats display. */
-  int subsurf_totvert;
-  int subsurf_totedge;
-  int subsurf_totpoly;
-  int subsurf_totloop;
-  char _pad2[2];
+  struct SubsurfRuntimeData *subsurf_runtime_data;
+  void *_pad1;
 
   /**
    * Caches for lazily computed vertex and polygon normals. These are stored here rather than in
    * #CustomData because they can be calculated on a const mesh, and adding custom data layers on a
    * const mesh is not thread-safe.
    */
+  char _pad2[6];
   char vert_normals_dirty;
   char poly_normals_dirty;
   float (*vert_normals)[3];
diff --git a/source/blender/makesdna/DNA_modifier_types.h b/source/blender/makesdna/DNA_modifier_types.h
index 6e3ce7e98a8..f148116eba8 100644
--- a/source/blender/makesdna/DNA_modifier_types.h
+++ b/source/blender/makesdna/DNA_modifier_types.h
@@ -178,13 +178,6 @@ typedef enum {
   SUBSURF_BOUNDARY_SMOOTH_PRESERVE_CORNERS = 1,
 } eSubsurfBoundarySmooth;
 
-typedef struct SubsurfRuntimeData {
-  /* Cached subdivision surface descriptor, with topology and settings. */
-  struct Subdiv *subdiv;
-  char set_by_draw_code;
-  char _pad[7];
-} SubsurfRuntimeData;
-
 typedef struct SubsurfModifierData {
   ModifierData modifier;