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, 49 insertions, 46 deletions

diff --git a/source/blender/blenkernel/intern/mesh_evaluate.cc b/source/blender/blenkernel/intern/mesh_evaluate.cc
index 9dba8eab340..7e52b96cc92 100644
--- a/source/blender/blenkernel/intern/mesh_evaluate.cc
+++ b/source/blender/blenkernel/intern/mesh_evaluate.cc
@@ -205,18 +205,13 @@ float BKE_mesh_calc_poly_area(const MPoly *mpoly, const MLoop *loopstart, const
 
 float BKE_mesh_calc_area(const Mesh *me)
 {
-  MVert *mvert = me->mvert;
-  MLoop *mloop = me->mloop;
-  MPoly *mpoly = me->mpoly;
+  const Span<MVert> verts = me->vertices();
+  const Span<MPoly> polys = me->polygons();
+  const Span<MLoop> loops = me->loops();
 
-  MPoly *mp;
-  int i = me->totpoly;
-  float total_area = 0;
-
-  for (mp = mpoly; i--; mp++) {
-    MLoop *ml_start = &mloop[mp->loopstart];
-
-    total_area += BKE_mesh_calc_poly_area(mp, ml_start, mvert);
+  float total_area = 0.0f;
+  for (const MPoly &poly : polys) {
+    total_area += BKE_mesh_calc_poly_area(&poly, &loops[poly.loopstart], verts.data());
   }
   return total_area;
 }
@@ -405,11 +400,10 @@ void BKE_mesh_poly_edgebitmap_insert(uint *edge_bitmap, const MPoly *mp, const M
 
 bool BKE_mesh_center_median(const Mesh *me, float r_cent[3])
 {
-  int i = me->totvert;
-  const MVert *mvert;
+  const Span<MVert> verts = me->vertices();
   zero_v3(r_cent);
-  for (mvert = me->mvert; i--; mvert++) {
-    add_v3_v3(r_cent, mvert->co);
+  for (const MVert &vert : verts) {
+    add_v3_v3(r_cent, vert.co);
   }
   /* otherwise we get NAN for 0 verts */
   if (me->totvert) {
@@ -420,18 +414,17 @@ bool BKE_mesh_center_median(const Mesh *me, float r_cent[3])
 
 bool BKE_mesh_center_median_from_polys(const Mesh *me, float r_cent[3])
 {
-  int i = me->totpoly;
   int tot = 0;
-  const MPoly *mpoly = me->mpoly;
-  const MLoop *mloop = me->mloop;
-  const MVert *mvert = me->mvert;
+  const Span<MVert> verts = me->vertices();
+  const Span<MPoly> polys = me->polygons();
+  const Span<MLoop> loops = me->loops();
   zero_v3(r_cent);
-  for (; i--; mpoly++) {
-    int loopend = mpoly->loopstart + mpoly->totloop;
-    for (int j = mpoly->loopstart; j < loopend; j++) {
-      add_v3_v3(r_cent, mvert[mloop[j].v].co);
+  for (const MPoly &poly : polys) {
+    int loopend = poly.loopstart + poly.totloop;
+    for (int j = poly.loopstart; j < loopend; j++) {
+      add_v3_v3(r_cent, verts[loops[j].v].co);
     }
-    tot += mpoly->totloop;
+    tot += poly.totloop;
   }
   /* otherwise we get NAN for 0 verts */
   if (me->totpoly) {
@@ -455,17 +448,19 @@ bool BKE_mesh_center_bounds(const Mesh *me, float r_cent[3])
 bool BKE_mesh_center_of_surface(const Mesh *me, float r_cent[3])
 {
   int i = me->totpoly;
-  MPoly *mpoly;
+  const MPoly *mpoly;
   float poly_area;
   float total_area = 0.0f;
   float poly_cent[3];
+  const MVert *verts = BKE_mesh_vertices(me);
+  const MPoly *polys = BKE_mesh_polygons(me);
+  const MLoop *loops = BKE_mesh_loops(me);
 
   zero_v3(r_cent);
 
   /* calculate a weighted average of polygon centroids */
-  for (mpoly = me->mpoly; i--; mpoly++) {
-    poly_area = mesh_calc_poly_area_centroid(
-        mpoly, me->mloop + mpoly->loopstart, me->mvert, poly_cent);
+  for (mpoly = polys; i--; mpoly++) {
+    poly_area = mesh_calc_poly_area_centroid(mpoly, loops + mpoly->loopstart, verts, poly_cent);
 
     madd_v3_v3fl(r_cent, poly_cent, poly_area);
     total_area += poly_area;
@@ -486,10 +481,13 @@ bool BKE_mesh_center_of_surface(const Mesh *me, float r_cent[3])
 bool BKE_mesh_center_of_volume(const Mesh *me, float r_cent[3])
 {
   int i = me->totpoly;
-  MPoly *mpoly;
+  const MPoly *mpoly;
   float poly_volume;
   float total_volume = 0.0f;
   float poly_cent[3];
+  const MVert *verts = BKE_mesh_vertices(me);
+  const MPoly *polys = BKE_mesh_polygons(me);
+  const MLoop *loops = BKE_mesh_loops(me);
 
   /* Use an initial center to avoid numeric instability of geometry far away from the center. */
   float init_cent[3];
@@ -498,9 +496,9 @@ bool BKE_mesh_center_of_volume(const Mesh *me, float r_cent[3])
   zero_v3(r_cent);
 
   /* calculate a weighted average of polyhedron centroids */
-  for (mpoly = me->mpoly; i--; mpoly++) {
+  for (mpoly = polys; i--; mpoly++) {
     poly_volume = mesh_calc_poly_volume_centroid_with_reference_center(
-        mpoly, me->mloop + mpoly->loopstart, me->mvert, init_cent, poly_cent);
+        mpoly, loops + mpoly->loopstart, verts, init_cent, poly_cent);
 
     /* poly_cent is already volume-weighted, so no need to multiply by the volume */
     add_v3_v3(r_cent, poly_cent);
@@ -670,7 +668,7 @@ void BKE_mesh_mdisp_flip(MDisps *md, const bool use_loop_mdisp_flip)
   }
 }
 
-void BKE_mesh_polygon_flip_ex(MPoly *mpoly,
+void BKE_mesh_polygon_flip_ex(const MPoly *mpoly,
                               MLoop *mloop,
                               CustomData *ldata,
                               float (*lnors)[3],
@@ -713,16 +711,16 @@ void BKE_mesh_polygon_flip_ex(MPoly *mpoly,
   }
 }
 
-void BKE_mesh_polygon_flip(MPoly *mpoly, MLoop *mloop, CustomData *ldata)
+void BKE_mesh_polygon_flip(const MPoly *mpoly, MLoop *mloop, CustomData *ldata)
 {
   MDisps *mdisp = (MDisps *)CustomData_get_layer(ldata, CD_MDISPS);
   BKE_mesh_polygon_flip_ex(mpoly, mloop, ldata, nullptr, mdisp, true);
 }
 
-void BKE_mesh_polygons_flip(MPoly *mpoly, MLoop *mloop, CustomData *ldata, int totpoly)
+void BKE_mesh_polygons_flip(const MPoly *mpoly, MLoop *mloop, CustomData *ldata, int totpoly)
 {
   MDisps *mdisp = (MDisps *)CustomData_get_layer(ldata, CD_MDISPS);
-  MPoly *mp;
+  const MPoly *mp;
   int i;
 
   for (mp = mpoly, i = 0; i < totpoly; mp++, i++) {
@@ -748,9 +746,9 @@ void BKE_mesh_flush_hidden_from_verts(Mesh *me)
     return;
   }
   const VArraySpan<bool> hide_vert_span{hide_vert};
-  const Span<MEdge> edges(me->medge, me->totedge);
-  const Span<MPoly> polys(me->mpoly, me->totpoly);
-  const Span<MLoop> loops(me->mloop, me->totloop);
+  const Span<MEdge> edges = me->edges();
+  const Span<MPoly> polys = me->polygons();
+  const Span<MLoop> loops = me->loops();
 
   /* Hide edges when either of their vertices are hidden. */
   SpanAttributeWriter<bool> hide_edge = attributes.lookup_or_add_for_write_only_span<bool>(
@@ -788,8 +786,8 @@ void BKE_mesh_flush_hidden_from_polys(Mesh *me)
     return;
   }
   const VArraySpan<bool> hide_poly_span{hide_poly};
-  const Span<MPoly> polys(me->mpoly, me->totpoly);
-  const Span<MLoop> loops(me->mloop, me->totloop);
+  const Span<MPoly> polys = me->polygons();
+  const Span<MLoop> loops = me->loops();
   SpanAttributeWriter<bool> hide_vert = attributes.lookup_or_add_for_write_only_span<bool>(
       ".hide_vert", ATTR_DOMAIN_POINT);
   SpanAttributeWriter<bool> hide_edge = attributes.lookup_or_add_for_write_only_span<bool>(
@@ -859,8 +857,13 @@ void BKE_mesh_flush_select_from_polys_ex(MVert *mvert,
 }
 void BKE_mesh_flush_select_from_polys(Mesh *me)
 {
-  BKE_mesh_flush_select_from_polys_ex(
-      me->mvert, me->totvert, me->mloop, me->medge, me->totedge, me->mpoly, me->totpoly);
+  BKE_mesh_flush_select_from_polys_ex(me->vertices_for_write().data(),
+                                      me->totvert,
+                                      me->loops().data(),
+                                      me->edges_for_write().data(),
+                                      me->totedge,
+                                      me->polygons().data(),
+                                      me->totpoly);
 }
 
 static void mesh_flush_select_from_verts(const Span<MVert> verts,
@@ -906,12 +909,12 @@ void BKE_mesh_flush_select_from_verts(Mesh *me)
 {
   const blender::bke::AttributeAccessor attributes = blender::bke::mesh_attributes(*me);
   mesh_flush_select_from_verts(
-      {me->mvert, me->totvert},
-      {me->mloop, me->totloop},
+      me->vertices(),
+      me->loops(),
       attributes.lookup_or_default<bool>(".hide_edge", ATTR_DOMAIN_EDGE, false),
       attributes.lookup_or_default<bool>(".hide_poly", ATTR_DOMAIN_FACE, false),
-      {me->medge, me->totedge},
-      {me->mpoly, me->totpoly});
+      me->edges_for_write(),
+      me->polygons_for_write());
 }
 
 /** \} */