Mesh: Remove redundant custom data pointers

For copy-on-write, we want to share attribute arrays between meshes
where possible. Mutable pointers like `Mesh.mvert` make that difficult
by making ownership vague. They also make code more complex by adding
redundancy.

The simplest solution is just removing them and retrieving layers from
`CustomData` as needed. Similar changes have already been applied to
curves and point clouds (e9f82d3dc7ee, 410a6efb747f). Removing use of
the pointers generally makes code more obvious and more reusable.

Mesh data is now accessed with a C++ API (`Mesh::edges()` or
`Mesh::edges_for_write()`), and a C API (`BKE_mesh_edges(mesh)`).

The CoW changes this commit makes possible are described in T95845
and T95842, and started in D14139 and D14140. The change also simplifies
the ongoing mesh struct-of-array refactors from T95965.

**RNA/Python Access Performance**
Theoretically, accessing mesh elements with the RNA API may become
slower, since the layer needs to be found on every random access.
However, overhead is already high enough that this doesn't make a
noticible differenc, and performance is actually improved in some
cases. Random access can be up to 10% faster, but other situations
might be a bit slower. Generally using `foreach_get/set` are the best
way to improve performance. See the differential revision for more
discussion about Python performance.

Cycles has been updated to use raw pointers and the internal Blender
mesh types, mostly because there is no sense in having this overhead
when it's already compiled with Blender. In my tests this roughly
halves the Cycles mesh creation time (0.19s to 0.10s for a 1 million
face grid).

Differential Revision: https://developer.blender.org/D15488

1 files changed, 13 insertions, 10 deletions

diff --git a/source/blender/blenkernel/intern/DerivedMesh.cc b/source/blender/blenkernel/intern/DerivedMesh.cc
index 7ef6eaa64cd..46a8caafa70 100644
--- a/source/blender/blenkernel/intern/DerivedMesh.cc
+++ b/source/blender/blenkernel/intern/DerivedMesh.cc
@@ -68,6 +68,8 @@
 
 using blender::float3;
 using blender::IndexRange;
+using blender::Span;
+using blender::VArray;
 
 /* very slow! enable for testing only! */
 //#define USE_MODIFIER_VALIDATE
@@ -585,7 +587,6 @@ static void add_orco_mesh(Object *ob, BMEditMesh *em, Mesh *mesh, Mesh *mesh_orc
 
     if (!(layerorco = (float(*)[3])CustomData_get_layer(&mesh->vdata, layer))) {
       CustomData_add_layer(&mesh->vdata, layer, CD_SET_DEFAULT, nullptr, mesh->totvert);
-      BKE_mesh_update_customdata_pointers(mesh, false);
 
       layerorco = (float(*)[3])CustomData_get_layer(&mesh->vdata, layer);
     }
@@ -2002,9 +2003,9 @@ void mesh_get_mapped_verts_coords(Mesh *me_eval, float (*r_cos)[3], const int to
     MEM_freeN(userData.vertex_visit);
   }
   else {
-    MVert *mv = me_eval->mvert;
-    for (int i = 0; i < totcos; i++, mv++) {
-      copy_v3_v3(r_cos[i], mv->co);
+    const Span<MVert> verts = me_eval->vertices();
+    for (int i = 0; i < totcos; i++) {
+      copy_v3_v3(r_cos[i], verts[i].co);
     }
   }
 }
@@ -2017,9 +2018,11 @@ static void mesh_init_origspace(Mesh *mesh)
                                                                    CD_ORIGSPACE_MLOOP);
   const int numpoly = mesh->totpoly;
   // const int numloop = mesh->totloop;
-  MVert *mv = mesh->mvert;
-  MLoop *ml = mesh->mloop;
-  MPoly *mp = mesh->mpoly;
+  const Span<MVert> verts = mesh->vertices();
+  const Span<MPoly> polys = mesh->polygons();
+  const Span<MLoop> loops = mesh->loops();
+
+  const MPoly *mp = polys.data();
   int i, j, k;
 
   blender::Vector<blender::float2, 64> vcos_2d;
@@ -2033,19 +2036,19 @@ static void mesh_init_origspace(Mesh *mesh)
       }
     }
     else {
-      MLoop *l = &ml[mp->loopstart];
+      const MLoop *l = &loops[mp->loopstart];
       float p_nor[3], co[3];
       float mat[3][3];
 
       float min[2] = {FLT_MAX, FLT_MAX}, max[2] = {-FLT_MAX, -FLT_MAX};
       float translate[2], scale[2];
 
-      BKE_mesh_calc_poly_normal(mp, l, mv, p_nor);
+      BKE_mesh_calc_poly_normal(mp, l, verts.data(), p_nor);
       axis_dominant_v3_to_m3(mat, p_nor);
 
       vcos_2d.resize(mp->totloop);
       for (j = 0; j < mp->totloop; j++, l++) {
-        mul_v3_m3v3(co, mat, mv[l->v].co);
+        mul_v3_m3v3(co, mat, verts[l->v].co);
         copy_v2_v2(vcos_2d[j], co);
 
         for (k = 0; k < 2; k++) {