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, 16 insertions, 10 deletions

diff --git a/source/blender/draw/intern/draw_cache_impl_subdivision.cc b/source/blender/draw/intern/draw_cache_impl_subdivision.cc
index e02bf57815d..9882ebf66f0 100644
--- a/source/blender/draw/intern/draw_cache_impl_subdivision.cc
+++ b/source/blender/draw/intern/draw_cache_impl_subdivision.cc
@@ -45,6 +45,8 @@
 #include "draw_cache_inline.h"
 #include "mesh_extractors/extract_mesh.hh"
 
+using blender::Span;
+
 extern "C" char datatoc_common_subdiv_custom_data_interp_comp_glsl[];
 extern "C" char datatoc_common_subdiv_ibo_lines_comp_glsl[];
 extern "C" char datatoc_common_subdiv_ibo_tris_comp_glsl[];
@@ -673,18 +675,19 @@ static void draw_subdiv_cache_extra_coarse_face_data_mesh(const MeshRenderData *
                                                           Mesh *mesh,
                                                           uint32_t *flags_data)
 {
-  for (int i = 0; i < mesh->totpoly; i++) {
+  const Span<MPoly> polys = mesh->polygons();
+  for (const int i : polys.index_range()) {
     uint32_t flag = 0;
-    if ((mesh->mpoly[i].flag & ME_SMOOTH) != 0) {
+    if ((polys[i].flag & ME_SMOOTH) != 0) {
       flag |= SUBDIV_COARSE_FACE_FLAG_SMOOTH;
     }
-    if ((mesh->mpoly[i].flag & ME_FACE_SEL) != 0) {
+    if ((polys[i].flag & ME_FACE_SEL) != 0) {
       flag |= SUBDIV_COARSE_FACE_FLAG_SELECT;
     }
     if (mr->hide_poly && mr->hide_poly[i]) {
       flag |= SUBDIV_COARSE_FACE_FLAG_HIDDEN;
     }
-    flags_data[i] = (uint)(mesh->mpoly[i].loopstart) | (flag << SUBDIV_COARSE_FACE_FLAG_OFFSET);
+    flags_data[i] = (uint)(polys[i].loopstart) | (flag << SUBDIV_COARSE_FACE_FLAG_OFFSET);
   }
 }
 
@@ -1092,6 +1095,7 @@ static bool draw_subdiv_build_cache(DRWSubdivCache *cache,
   }
 
   /* Only build polygon related data if we have polygons. */
+  const Span<MPoly> polys = mesh_eval->polygons();
   if (cache->num_subdiv_loops != 0) {
     /* Build buffers for the PatchMap. */
     draw_patch_map_build(&cache->gpu_patch_map, subdiv);
@@ -1105,7 +1109,7 @@ static bool draw_subdiv_build_cache(DRWSubdivCache *cache,
         GPU_vertbuf_get_data(cache->fdots_patch_coords);
     for (int i = 0; i < mesh_eval->totpoly; i++) {
       const int ptex_face_index = cache->face_ptex_offset[i];
-      if (mesh_eval->mpoly[i].totloop == 4) {
+      if (polys[i].totloop == 4) {
         /* For quads, the center coordinate of the coarse face has `u = v = 0.5`. */
         blender_fdots_patch_coords[i] = make_patch_coord(ptex_face_index, 0.5f, 0.5f);
       }
@@ -1118,16 +1122,16 @@ static bool draw_subdiv_build_cache(DRWSubdivCache *cache,
     }
 
     cache->subdiv_polygon_offset_buffer = draw_subdiv_build_origindex_buffer(
-        cache->subdiv_polygon_offset, mesh_eval->totpoly);
+        cache->subdiv_polygon_offset, polys.size());
 
     cache->face_ptex_offset_buffer = draw_subdiv_build_origindex_buffer(cache->face_ptex_offset,
-                                                                        mesh_eval->totpoly + 1);
+                                                                        polys.size() + 1);
 
     build_vertex_face_adjacency_maps(cache);
   }
 
   cache->resolution = to_mesh_settings.resolution;
-  cache->num_coarse_poly = mesh_eval->totpoly;
+  cache->num_coarse_poly = polys.size();
 
   /* To avoid floating point precision issues when evaluating patches at patch boundaries,
    * ensure that all loops sharing a vertex use the same patch coordinate. This could cause
@@ -2152,9 +2156,10 @@ void DRW_subdivide_loose_geom(DRWSubdivCache *subdiv_cache, MeshBufferCache *cac
   int subd_vert_offset = 0;
 
   /* Subdivide each loose coarse edge. */
+  const Span<MEdge> coarse_edges = coarse_mesh->edges();
   for (int i = 0; i < coarse_loose_edge_len; i++) {
     const int coarse_edge_index = cache->loose_geom.edges[i];
-    const MEdge *coarse_edge = &coarse_mesh->medge[cache->loose_geom.edges[i]];
+    const MEdge *coarse_edge = &coarse_edges[cache->loose_geom.edges[i]];
 
     /* Perform interpolation of each vertex. */
     for (int i = 0; i < resolution - 1; i++, subd_edge_offset++) {
@@ -2182,9 +2187,10 @@ void DRW_subdivide_loose_geom(DRWSubdivCache *subdiv_cache, MeshBufferCache *cac
   }
 
   /* Copy the remaining loose_verts. */
+  const Span<MVert> coarse_verts = coarse_mesh->vertices();
   for (int i = 0; i < coarse_loose_vert_len; i++) {
     const int coarse_vertex_index = cache->loose_geom.verts[i];
-    const MVert &coarse_vertex = coarse_mesh->mvert[coarse_vertex_index];
+    const MVert &coarse_vertex = coarse_verts[coarse_vertex_index];
 
     DRWSubdivLooseVertex &subd_v = loose_subd_verts[subd_vert_offset++];
     subd_v.coarse_vertex_index = cache->loose_geom.verts[i];