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, 33 insertions, 34 deletions

diff --git a/source/blender/io/usd/intern/usd_reader_mesh.cc b/source/blender/io/usd/intern/usd_reader_mesh.cc
index 4155f6ac40f..86e3aeece5d 100644
--- a/source/blender/io/usd/intern/usd_reader_mesh.cc
+++ b/source/blender/io/usd/intern/usd_reader_mesh.cc
@@ -312,15 +312,15 @@ bool USDMeshReader::topology_changed(const Mesh *existing_mesh, const double mot
 
 void USDMeshReader::read_mpolys(Mesh *mesh)
 {
-  MPoly *mpolys = mesh->mpoly;
-  MLoop *mloops = mesh->mloop;
+  MutableSpan<MPoly> polys = mesh->polygons_for_write();
+  MutableSpan<MLoop> loops = mesh->loops_for_write();
 
   int loop_index = 0;
 
   for (int i = 0; i < face_counts_.size(); i++) {
     const int face_size = face_counts_[i];
 
-    MPoly &poly = mpolys[i];
+    MPoly &poly = polys[i];
     poly.loopstart = loop_index;
     poly.totloop = face_size;
 
@@ -331,12 +331,12 @@ void USDMeshReader::read_mpolys(Mesh *mesh)
     if (is_left_handed_) {
       int loop_end_index = loop_index + (face_size - 1);
       for (int f = 0; f < face_size; ++f, ++loop_index) {
-        mloops[loop_index].v = face_indices_[loop_end_index - f];
+        loops[loop_index].v = face_indices_[loop_end_index - f];
       }
     }
     else {
       for (int f = 0; f < face_size; ++f, ++loop_index) {
-        mloops[loop_index].v = face_indices_[loop_index];
+        loops[loop_index].v = face_indices_[loop_index];
       }
     }
   }
@@ -400,6 +400,7 @@ void USDMeshReader::read_uvs(Mesh *mesh, const double motionSampleTime, const bo
     }
   }
 
+  const Span<MLoop> loops = mesh->loops();
   for (int i = 0; i < face_counts_.size(); i++) {
     const int face_size = face_counts_[i];
 
@@ -435,7 +436,7 @@ void USDMeshReader::read_uvs(Mesh *mesh, const double motionSampleTime, const bo
 
         /* For Vertex interpolation, use the vertex index. */
         int usd_uv_index = sample.interpolation == pxr::UsdGeomTokens->vertex ?
-                               mesh->mloop[loop_index].v :
+                               loops[loop_index].v :
                                loop_index;
 
         if (usd_uv_index >= sample.uvs.size()) {
@@ -515,24 +516,23 @@ void USDMeshReader::read_colors(Mesh *mesh, const double motionSampleTime)
 
   MLoopCol *colors = static_cast<MLoopCol *>(cd_ptr);
 
-  mesh->mloopcol = colors;
-
-  MPoly *poly = mesh->mpoly;
-
-  for (int i = 0, e = mesh->totpoly; i < e; ++i, ++poly) {
-    for (int j = 0; j < poly->totloop; ++j) {
-      int loop_index = poly->loopstart + j;
+  const Span<MPoly> polys = mesh->polygons();
+  const Span<MLoop> loops = mesh->loops();
+  for (const int i : polys.index_range()) {
+    const MPoly &poly = polys[i];
+    for (int j = 0; j < poly.totloop; ++j) {
+      int loop_index = poly.loopstart + j;
 
       /* Default for constant varying interpolation. */
       int usd_index = 0;
 
       if (interp == pxr::UsdGeomTokens->vertex) {
-        usd_index = mesh->mloop[loop_index].v;
+        usd_index = loops[loop_index].v;
       }
       else if (interp == pxr::UsdGeomTokens->faceVarying) {
-        usd_index = poly->loopstart;
+        usd_index = poly.loopstart;
         if (is_left_handed_) {
-          usd_index += poly->totloop - 1 - j;
+          usd_index += poly.totloop - 1 - j;
         }
         else {
           usd_index += j;
@@ -630,15 +630,15 @@ void USDMeshReader::process_normals_face_varying(Mesh *mesh)
   float(*lnors)[3] = static_cast<float(*)[3]>(
       MEM_malloc_arrayN(loop_count, sizeof(float[3]), "USD::FaceNormals"));
 
-  MPoly *mpoly = mesh->mpoly;
-
-  for (int i = 0, e = mesh->totpoly; i < e; ++i, ++mpoly) {
-    for (int j = 0; j < mpoly->totloop; j++) {
-      int blender_index = mpoly->loopstart + j;
+  const Span<MPoly> polys = mesh->polygons();
+  for (const int i : polys.index_range()) {
+    const MPoly &poly = polys[i];
+    for (int j = 0; j < poly.totloop; j++) {
+      int blender_index = poly.loopstart + j;
 
-      int usd_index = mpoly->loopstart;
+      int usd_index = poly.loopstart;
       if (is_left_handed_) {
-        usd_index += mpoly->totloop - 1 - j;
+        usd_index += poly.totloop - 1 - j;
       }
       else {
         usd_index += j;
@@ -671,12 +671,11 @@ void USDMeshReader::process_normals_uniform(Mesh *mesh)
   float(*lnors)[3] = static_cast<float(*)[3]>(
       MEM_malloc_arrayN(mesh->totloop, sizeof(float[3]), "USD::FaceNormals"));
 
-  MPoly *mpoly = mesh->mpoly;
-
-  for (int i = 0, e = mesh->totpoly; i < e; ++i, ++mpoly) {
-
-    for (int j = 0; j < mpoly->totloop; j++) {
-      int loop_index = mpoly->loopstart + j;
+  const Span<MPoly> polys = mesh->polygons();
+  for (const int i : polys.index_range()) {
+    const MPoly &poly = polys[i];
+    for (int j = 0; j < poly.totloop; j++) {
+      int loop_index = poly.loopstart + j;
       lnors[loop_index][0] = normals_[i][0];
       lnors[loop_index][1] = normals_[i][1];
       lnors[loop_index][2] = normals_[i][2];
@@ -699,8 +698,9 @@ void USDMeshReader::read_mesh_sample(ImportSettings *settings,
    * in code that expect this data to be there. */
 
   if (new_mesh || (settings->read_flag & MOD_MESHSEQ_READ_VERT) != 0) {
+    MutableSpan<MVert> verts = mesh->vertices_for_write();
     for (int i = 0; i < positions_.size(); i++) {
-      MVert &mvert = mesh->mvert[i];
+      MVert &mvert = verts[i];
       mvert.co[0] = positions_[i][0];
       mvert.co[1] = positions_[i][1];
       mvert.co[2] = positions_[i][2];
@@ -903,8 +903,7 @@ Mesh *USDMeshReader::read_mesh(Mesh *existing_mesh,
         existing_mesh, positions_.size(), 0, 0, face_indices_.size(), face_counts_.size());
 
     for (pxr::TfToken token : uv_tokens) {
-      void *cd_ptr = add_customdata_cb(active_mesh, token.GetText(), CD_MLOOPUV);
-      active_mesh->mloopuv = static_cast<MLoopUV *>(cd_ptr);
+      add_customdata_cb(active_mesh, token.GetText(), CD_MLOOPUV);
     }
   }
 
@@ -914,8 +913,8 @@ Mesh *USDMeshReader::read_mesh(Mesh *existing_mesh,
     /* Here we assume that the number of materials doesn't change, i.e. that
      * the material slots that were created when the object was loaded from
      * USD are still valid now. */
-    size_t num_polys = active_mesh->totpoly;
-    if (num_polys > 0 && import_params_.import_materials) {
+    MutableSpan<MPoly> polys = active_mesh->polygons_for_write();
+    if (!polys.is_empty() && import_params_.import_materials) {
       std::map<pxr::SdfPath, int> mat_map;
       bke::MutableAttributeAccessor attributes = bke::mesh_attributes_for_write(*active_mesh);
       bke::SpanAttributeWriter<int> material_indices =