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, 36 insertions, 20 deletions

diff --git a/source/blender/blenkernel/intern/paint.cc b/source/blender/blenkernel/intern/paint.cc
index 4c3da5eabc4..10dfa3f59e7 100644
--- a/source/blender/blenkernel/intern/paint.cc
+++ b/source/blender/blenkernel/intern/paint.cc
@@ -64,6 +64,9 @@
 
 #include "bmesh.h"
 
+using blender::MutableSpan;
+using blender::Span;
+
 static void palette_init_data(ID *id)
 {
   Palette *palette = (Palette *)id;
@@ -1624,7 +1627,7 @@ static void sculpt_update_object(Depsgraph *depsgraph,
   Scene *scene = DEG_get_input_scene(depsgraph);
   Sculpt *sd = scene->toolsettings->sculpt;
   SculptSession *ss = ob->sculpt;
-  const Mesh *me = BKE_object_get_original_mesh(ob);
+  Mesh *me = BKE_object_get_original_mesh(ob);
   Mesh *me_eval = BKE_object_get_evaluated_mesh(ob_eval);
   MultiresModifierData *mmd = BKE_sculpt_multires_active(scene, ob);
   const bool use_face_sets = (ob->mode & OB_MODE_SCULPT) != 0;
@@ -1664,17 +1667,17 @@ static void sculpt_update_object(Depsgraph *depsgraph,
 
     /* These are assigned to the base mesh in Multires. This is needed because Face Sets operators
      * and tools use the Face Sets data from the base mesh when Multires is active. */
-    ss->mvert = me->mvert;
-    ss->mpoly = me->mpoly;
-    ss->mloop = me->mloop;
+    ss->mvert = BKE_mesh_vertices_for_write(me);
+    ss->mpoly = BKE_mesh_polygons(me);
+    ss->mloop = BKE_mesh_loops(me);
   }
   else {
     ss->totvert = me->totvert;
     ss->totpoly = me->totpoly;
     ss->totfaces = me->totpoly;
-    ss->mvert = me->mvert;
-    ss->mpoly = me->mpoly;
-    ss->mloop = me->mloop;
+    ss->mvert = BKE_mesh_vertices_for_write(me);
+    ss->mpoly = BKE_mesh_polygons(me);
+    ss->mloop = BKE_mesh_loops(me);
     ss->multires.active = false;
     ss->multires.modifier = nullptr;
     ss->multires.level = 0;
@@ -1724,8 +1727,13 @@ static void sculpt_update_object(Depsgraph *depsgraph,
   BKE_pbvh_face_sets_color_set(ss->pbvh, me->face_sets_color_seed, me->face_sets_color_default);
 
   if (need_pmap && ob->type == OB_MESH && !ss->pmap) {
-    BKE_mesh_vert_poly_map_create(
-        &ss->pmap, &ss->pmap_mem, me->mpoly, me->mloop, me->totvert, me->totpoly, me->totloop);
+    BKE_mesh_vert_poly_map_create(&ss->pmap,
+                                  &ss->pmap_mem,
+                                  BKE_mesh_polygons(me),
+                                  BKE_mesh_loops(me),
+                                  me->totvert,
+                                  me->totpoly,
+                                  me->totloop);
 
     if (ss->pbvh) {
       BKE_pbvh_pmap_set(ss->pbvh, ss->pmap);
@@ -1743,7 +1751,8 @@ static void sculpt_update_object(Depsgraph *depsgraph,
       /* If the fully evaluated mesh has the same topology as the deform-only version, use it.
        * This matters because 'deform eval' is very restrictive and excludes even modifiers that
        * simply recompute vertex weights. */
-      if (me_eval_deform->mpoly == me_eval->mpoly && me_eval_deform->mloop == me_eval->mloop &&
+      if (me_eval_deform->polygons().data() == me_eval->polygons().data() &&
+          me_eval_deform->loops().data() == me_eval->loops().data() &&
           me_eval_deform->totvert == me_eval->totvert) {
         me_eval_deform = me_eval;
       }
@@ -1921,7 +1930,7 @@ void BKE_sculpt_color_layer_create_if_needed(Object *object)
   CustomDataLayer *layer = orig_me->vdata.layers +
                            CustomData_get_layer_index(&orig_me->vdata, CD_PROP_COLOR);
 
-  BKE_mesh_update_customdata_pointers(orig_me, true);
+  BKE_mesh_tessface_clear(orig_me);
 
   BKE_id_attributes_active_color_set(&orig_me->id, layer);
   DEG_id_tag_update(&orig_me->id, ID_RECALC_GEOMETRY_ALL_MODES);
@@ -1944,6 +1953,8 @@ void BKE_sculpt_update_object_for_edit(
 int BKE_sculpt_mask_layers_ensure(Object *ob, MultiresModifierData *mmd)
 {
   Mesh *me = static_cast<Mesh *>(ob->data);
+  const Span<MPoly> polys = me->polygons();
+  const Span<MLoop> loops = me->loops();
   int ret = 0;
 
   const float *paint_mask = static_cast<const float *>(
@@ -1972,12 +1983,12 @@ int BKE_sculpt_mask_layers_ensure(Object *ob, MultiresModifierData *mmd)
     /* if vertices already have mask, copy into multires data */
     if (paint_mask) {
       for (i = 0; i < me->totpoly; i++) {
-        const MPoly *p = &me->mpoly[i];
+        const MPoly *p = &polys[i];
         float avg = 0;
 
         /* mask center */
         for (j = 0; j < p->totloop; j++) {
-          const MLoop *l = &me->mloop[p->loopstart + j];
+          const MLoop *l = &loops[p->loopstart + j];
           avg += paint_mask[l->v];
         }
         avg /= (float)p->totloop;
@@ -1985,9 +1996,9 @@ int BKE_sculpt_mask_layers_ensure(Object *ob, MultiresModifierData *mmd)
         /* fill in multires mask corner */
         for (j = 0; j < p->totloop; j++) {
           GridPaintMask *gpm = &gmask[p->loopstart + j];
-          const MLoop *l = &me->mloop[p->loopstart + j];
-          const MLoop *prev = ME_POLY_LOOP_PREV(me->mloop, p, j);
-          const MLoop *next = ME_POLY_LOOP_NEXT(me->mloop, p, j);
+          const MLoop *l = &loops[p->loopstart + j];
+          const MLoop *prev = ME_POLY_LOOP_PREV(loops, p, j);
+          const MLoop *next = ME_POLY_LOOP_NEXT(loops, p, j);
 
           gpm->data[0] = avg;
           gpm->data[1] = (paint_mask[l->v] + paint_mask[next->v]) * 0.5f;
@@ -2234,18 +2245,23 @@ static PBVH *build_pbvh_from_regular_mesh(Object *ob, Mesh *me_eval_deform, bool
   PBVH *pbvh = BKE_pbvh_new();
   BKE_pbvh_respect_hide_set(pbvh, respect_hide);
 
+  MutableSpan<MVert> verts = me->vertices_for_write();
+  const Span<MPoly> polys = me->polygons();
+  const Span<MLoop> loops = me->loops();
+
   MLoopTri *looptri = static_cast<MLoopTri *>(
       MEM_malloc_arrayN(looptris_num, sizeof(*looptri), __func__));
 
-  BKE_mesh_recalc_looptri(me->mloop, me->mpoly, me->mvert, me->totloop, me->totpoly, looptri);
+  BKE_mesh_recalc_looptri(
+      loops.data(), polys.data(), verts.data(), me->totloop, me->totpoly, looptri);
 
   BKE_sculpt_sync_face_set_visibility(me, nullptr);
 
   BKE_pbvh_build_mesh(pbvh,
                       me,
-                      me->mpoly,
-                      me->mloop,
-                      me->mvert,
+                      polys.data(),
+                      loops.data(),
+                      verts.data(),
                       me->totvert,
                       &me->vdata,
                       &me->ldata,