Metaball: Evaluate metaball objects as mesh components

With the ultimate goal of simplifying drawing and evaluation,
this patch makes the following changes and removes code:
- Use `Mesh` instead of `DispList` for evaluated basis metaballs.
- Remove all `DispList` drawing code, which is now unused.
- Simplify code that converts evaluated metaballs to meshes.
- Store the evaluated mesh in the evaluated geometry set.

This has the following indirect benefits:
- Evaluated meshes from metaball objects can be used in geometry nodes.
- Renderers can ignore evaluated metaball objects completely
- Cycles rendering no longer has to convert to mesh from `DispList`.
- We get closer to removing `DispList` completely.
- Optimizations to mesh rendering will also apply to metaball objects.

The vertex normals on the evaluated mesh are technically invalid;
the regular calculation wouldn't reproduce them. Metaball objects
don't support modifiers though, so it shouldn't be a problem.
Eventually we can support per-vertex custom normals (T93551).

Differential Revision: https://developer.blender.org/D14593

1 files changed, 9 insertions, 3 deletions

diff --git a/source/blender/blenkernel/intern/object_update.c b/source/blender/blenkernel/intern/object_update.c
index af0c5107348..5656a9f6c92 100644
--- a/source/blender/blenkernel/intern/object_update.c
+++ b/source/blender/blenkernel/intern/object_update.c
@@ -168,7 +168,7 @@ void BKE_object_handle_data_update(Depsgraph *depsgraph, Scene *scene, Object *o
       break;
 
     case OB_MBALL:
-      BKE_displist_make_mball(depsgraph, scene, ob);
+      BKE_mball_data_update(depsgraph, scene, ob);
       break;
 
     case OB_CURVES_LEGACY:
@@ -292,9 +292,15 @@ void BKE_object_batch_cache_dirty_tag(Object *ob)
     case OB_CURVES_LEGACY:
       BKE_curve_batch_cache_dirty_tag((struct Curve *)ob->data, BKE_CURVE_BATCH_DIRTY_ALL);
       break;
-    case OB_MBALL:
-      BKE_mball_batch_cache_dirty_tag((struct MetaBall *)ob->data, BKE_MBALL_BATCH_DIRTY_ALL);
+    case OB_MBALL: {
+      /* This function is currently called on original objects, so to properly
+       * clear the actual displayed geometry, we have to tag the evaluated mesh. */
+      Mesh *mesh = BKE_object_get_evaluated_mesh_no_subsurf(ob);
+      if (mesh) {
+        BKE_mesh_batch_cache_dirty_tag(mesh, BKE_MESH_BATCH_DIRTY_ALL);
+      }
       break;
+    }
     case OB_GPENCIL:
       BKE_gpencil_batch_cache_dirty_tag((struct bGPdata *)ob->data);
       break;