Mesh: Use cached looptris in draw cache extraction

The mesh's triangulation cache is often created for other operations
besides the drawing code, but during the mesh draw cache extraction
it is recalculated on every single time. It is simpler and faster to use
the existing MLoopTri array. It can also save memory if the cache
already exists by avoiding allocating a duplicate array. For a 4 million
face quad mesh, that is already 128 MB.

Also use face normals for mesh triangulation if they aren't dirty,
which should provide a general speedup when they're both necessary.

Recently 54182e4925de made this more reliable, since the triangulation
cache is invalidated properly when the mesh is deformed.

Fixes T98073

Differential Revision: https://developer.blender.org/D15550

1 files changed, 17 insertions, 6 deletions

diff --git a/source/blender/blenkernel/intern/mesh_runtime.cc b/source/blender/blenkernel/intern/mesh_runtime.cc
index 4b6433edd5a..d7a0b73298e 100644
--- a/source/blender/blenkernel/intern/mesh_runtime.cc
+++ b/source/blender/blenkernel/intern/mesh_runtime.cc
@@ -154,12 +154,23 @@ void BKE_mesh_runtime_looptri_recalc(Mesh *mesh)
   const Span<MPoly> polys = mesh->polys();
   const Span<MLoop> loops = mesh->loops();
 
-  BKE_mesh_recalc_looptri(loops.data(),
-                          polys.data(),
-                          verts.data(),
-                          mesh->totloop,
-                          mesh->totpoly,
-                          mesh->runtime.looptris.array_wip);
+  if (BKE_mesh_poly_normals_are_dirty(mesh)) {
+    BKE_mesh_recalc_looptri_with_normals(loops.data(),
+                                         polys.data(),
+                                         verts.data(),
+                                         mesh->totloop,
+                                         mesh->totpoly,
+                                         mesh->runtime.looptris.array_wip,
+                                         BKE_mesh_poly_normals_ensure(mesh));
+  }
+  else {
+    BKE_mesh_recalc_looptri(loops.data(),
+                            polys.data(),
+                            verts.data(),
+                            mesh->totloop,
+                            mesh->totpoly,
+                            mesh->runtime.looptris.array_wip);
+  }
 
   BLI_assert(mesh->runtime.looptris.array == nullptr);
   atomic_cas_ptr((void **)&mesh->runtime.looptris.array,