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, 151 insertions, 77 deletions

diff --git a/intern/cycles/blender/mesh.cpp b/intern/cycles/blender/mesh.cpp
index 2e2dfd6583b..47c3ff65aae 100644
--- a/intern/cycles/blender/mesh.cpp
+++ b/intern/cycles/blender/mesh.cpp
@@ -26,6 +26,8 @@
 
 #include "mikktspace.h"
 
+#include "DNA_meshdata_types.h"
+
 CCL_NAMESPACE_BEGIN
 
 /* Tangent Space */
@@ -279,10 +281,15 @@ static void fill_generic_attribute(BL::Mesh &b_mesh,
   switch (b_domain) {
     case BL::Attribute::domain_CORNER: {
       if (subdivision) {
-        for (BL::MeshPolygon &p : b_mesh.polygons) {
-          int n = p.loop_total();
-          for (int i = 0; i < n; i++) {
-            *data = get_value_at_index(p.loop_start() + i);
+        const int polys_num = b_mesh.polygons.length();
+        if (polys_num == 0) {
+          return;
+        }
+        const MPoly *polys = static_cast<const MPoly *>(b_mesh.polygons[0].ptr.data);
+        for (int i = 0; i < polys_num; i++) {
+          const MPoly &b_poly = polys[i];
+          for (int j = 0; j < b_poly.totloop; j++) {
+            *data = get_value_at_index(b_poly.loopstart + j);
             data++;
           }
         }
@@ -299,27 +306,32 @@ static void fill_generic_attribute(BL::Mesh &b_mesh,
       break;
     }
     case BL::Attribute::domain_EDGE: {
+      const size_t edges_num = b_mesh.edges.length();
+      if (edges_num == 0) {
+        return;
+      }
       if constexpr (std::is_same_v<TypeInCycles, uchar4>) {
         /* uchar4 edge attributes do not exist, and averaging in place
          * would not work. */
         assert(0);
       }
       else {
-        /* Average edge attributes at vertices. */
-        const size_t num_verts = b_mesh.vertices.length();
-        vector<int> count(num_verts, 0);
-
-        for (BL::MeshEdge &e : b_mesh.edges) {
-          BL::Array<int, 2> vertices = e.vertices();
-          TypeInCycles value = get_value_at_index(e.index());
+        const MEdge *edges = static_cast<const MEdge *>(b_mesh.edges[0].ptr.data);
+        const size_t verts_num = b_mesh.vertices.length();
+        vector<int> count(verts_num, 0);
 
-          data[vertices[0]] += value;
-          data[vertices[1]] += value;
-          count[vertices[0]]++;
-          count[vertices[1]]++;
+        /* Average edge attributes at vertices. */
+        for (int i = 0; i < edges_num; i++) {
+          TypeInCycles value = get_value_at_index(i);
+
+          const MEdge &b_edge = edges[i];
+          data[b_edge.v1] += value;
+          data[b_edge.v2] += value;
+          count[b_edge.v1]++;
+          count[b_edge.v2]++;
         }
 
-        for (size_t i = 0; i < num_verts; i++) {
+        for (size_t i = 0; i < verts_num; i++) {
           if (count[i] > 1) {
             data[i] /= (float)count[i];
           }
@@ -603,6 +615,12 @@ static void attr_create_uv_map(Scene *scene, Mesh *mesh, BL::Mesh &b_mesh)
 
 static void attr_create_subd_uv_map(Scene *scene, Mesh *mesh, BL::Mesh &b_mesh, bool subdivide_uvs)
 {
+  const int polys_num = b_mesh.polygons.length();
+  if (polys_num == 0) {
+    return;
+  }
+  const MPoly *polys = static_cast<const MPoly *>(b_mesh.polygons[0].ptr.data);
+
   if (!b_mesh.uv_layers.empty()) {
     BL::Mesh::uv_layers_iterator l;
     int i = 0;
@@ -636,10 +654,10 @@ static void attr_create_subd_uv_map(Scene *scene, Mesh *mesh, BL::Mesh &b_mesh,
 
         float2 *fdata = uv_attr->data_float2();
 
-        for (BL::MeshPolygon &p : b_mesh.polygons) {
-          int n = p.loop_total();
-          for (int j = 0; j < n; j++) {
-            *(fdata++) = get_float2(l->data[p.loop_start() + j].uv());
+        for (int i = 0; i < polys_num; i++) {
+          const MPoly &b_poly = polys[i];
+          for (int j = 0; j < b_poly.totloop; j++) {
+            *(fdata++) = get_float2(l->data[b_poly.loopstart + j].uv());
           }
         }
       }
@@ -702,6 +720,8 @@ static void attr_create_pointiness(Scene *scene, Mesh *mesh, BL::Mesh &b_mesh, b
   if (num_verts == 0) {
     return;
   }
+  const MVert *verts = static_cast<const MVert *>(b_mesh.vertices[0].ptr.data);
+
   /* STEP 1: Find out duplicated vertices and point duplicates to a single
    *         original vertex.
    */
@@ -754,10 +774,12 @@ static void attr_create_pointiness(Scene *scene, Mesh *mesh, BL::Mesh &b_mesh, b
    */
   vector<float3> vert_normal(num_verts, zero_float3());
   /* First we accumulate all vertex normals in the original index. */
+  const float(*b_vert_normals)[3] = static_cast<const float(*)[3]>(
+      b_mesh.vertex_normals[0].ptr.data);
   for (int vert_index = 0; vert_index < num_verts; ++vert_index) {
-    const float3 normal = get_float3(b_mesh.vertices[vert_index].normal());
+    const float *b_vert_normal = b_vert_normals[vert_index];
     const int orig_index = vert_orig_index[vert_index];
-    vert_normal[orig_index] += normal;
+    vert_normal[orig_index] += make_float3(b_vert_normal[0], b_vert_normal[1], b_vert_normal[2]);
   }
   /* Then we normalize the accumulated result and flush it to all duplicates
    * as well.
@@ -770,18 +792,24 @@ static void attr_create_pointiness(Scene *scene, Mesh *mesh, BL::Mesh &b_mesh, b
   vector<int> counter(num_verts, 0);
   vector<float> raw_data(num_verts, 0.0f);
   vector<float3> edge_accum(num_verts, zero_float3());
-  BL::Mesh::edges_iterator e;
   EdgeMap visited_edges;
-  int edge_index = 0;
   memset(&counter[0], 0, sizeof(int) * counter.size());
-  for (b_mesh.edges.begin(e); e != b_mesh.edges.end(); ++e, ++edge_index) {
-    const int v0 = vert_orig_index[b_mesh.edges[edge_index].vertices()[0]],
-              v1 = vert_orig_index[b_mesh.edges[edge_index].vertices()[1]];
+
+  const MEdge *edges = static_cast<MEdge *>(b_mesh.edges[0].ptr.data);
+  const int edges_num = b_mesh.edges.length();
+
+  for (int i = 0; i < edges_num; i++) {
+    const MEdge &b_edge = edges[i];
+    const int v0 = vert_orig_index[b_edge.v1];
+    const int v1 = vert_orig_index[b_edge.v2];
     if (visited_edges.exists(v0, v1)) {
       continue;
     }
     visited_edges.insert(v0, v1);
-    float3 co0 = get_float3(b_mesh.vertices[v0].co()), co1 = get_float3(b_mesh.vertices[v1].co());
+    const MVert &b_vert_0 = verts[v0];
+    const MVert &b_vert_1 = verts[v1];
+    float3 co0 = make_float3(b_vert_0.co[0], b_vert_0.co[1], b_vert_0.co[2]);
+    float3 co1 = make_float3(b_vert_1.co[0], b_vert_1.co[1], b_vert_1.co[2]);
     float3 edge = normalize(co1 - co0);
     edge_accum[v0] += edge;
     edge_accum[v1] += -edge;
@@ -809,11 +837,11 @@ static void attr_create_pointiness(Scene *scene, Mesh *mesh, BL::Mesh &b_mesh, b
   float *data = attr->data_float();
   memcpy(data, &raw_data[0], sizeof(float) * raw_data.size());
   memset(&counter[0], 0, sizeof(int) * counter.size());
-  edge_index = 0;
   visited_edges.clear();
-  for (b_mesh.edges.begin(e); e != b_mesh.edges.end(); ++e, ++edge_index) {
-    const int v0 = vert_orig_index[b_mesh.edges[edge_index].vertices()[0]],
-              v1 = vert_orig_index[b_mesh.edges[edge_index].vertices()[1]];
+  for (int i = 0; i < edges_num; i++) {
+    const MEdge &b_edge = edges[i];
+    const int v0 = vert_orig_index[b_edge.v1];
+    const int v1 = vert_orig_index[b_edge.v2];
     if (visited_edges.exists(v0, v1)) {
       continue;
     }
@@ -852,6 +880,7 @@ static void attr_create_random_per_island(Scene *scene,
     return;
   }
 
+  const int polys_num = b_mesh.polygons.length();
   int number_of_vertices = b_mesh.vertices.length();
   if (number_of_vertices == 0) {
     return;
@@ -859,8 +888,11 @@ static void attr_create_random_per_island(Scene *scene,
 
   DisjointSet vertices_sets(number_of_vertices);
 
-  for (BL::MeshEdge &e : b_mesh.edges) {
-    vertices_sets.join(e.vertices()[0], e.vertices()[1]);
+  const MEdge *edges = static_cast<MEdge *>(b_mesh.edges[0].ptr.data);
+  const int edges_num = b_mesh.edges.length();
+
+  for (int i = 0; i < edges_num; i++) {
+    vertices_sets.join(edges[i].v1, edges[i].v2);
   }
 
   AttributeSet &attributes = (subdivision) ? mesh->subd_attributes : mesh->attributes;
@@ -873,8 +905,14 @@ static void attr_create_random_per_island(Scene *scene,
     }
   }
   else {
-    for (BL::MeshPolygon &p : b_mesh.polygons) {
-      data[p.index()] = hash_uint_to_float(vertices_sets.find(p.vertices()[0]));
+    if (polys_num != 0) {
+      const MPoly *polys = static_cast<const MPoly *>(b_mesh.polygons[0].ptr.data);
+      const MLoop *loops = static_cast<const MLoop *>(b_mesh.loops[0].ptr.data);
+      for (int i = 0; i < polys_num; i++) {
+        const MPoly &b_poly = polys[i];
+        const MLoop &b_loop = loops[b_poly.loopstart];
+        data[i] = hash_uint_to_float(vertices_sets.find(b_loop.v));
+      }
     }
   }
 }
@@ -909,6 +947,7 @@ static void create_mesh(Scene *scene,
 {
   /* count vertices and faces */
   int numverts = b_mesh.vertices.length();
+  const int polys_num = b_mesh.polygons.length();
   int numfaces = (!subdivision) ? b_mesh.loop_triangles.length() : b_mesh.polygons.length();
   int numtris = 0;
   int numcorners = 0;
@@ -921,13 +960,17 @@ static void create_mesh(Scene *scene,
     return;
   }
 
+  const MVert *verts = static_cast<const MVert *>(b_mesh.vertices[0].ptr.data);
+
   if (!subdivision) {
     numtris = numfaces;
   }
   else {
-    for (BL::MeshPolygon &p : b_mesh.polygons) {
-      numngons += (p.loop_total() == 4) ? 0 : 1;
-      numcorners += p.loop_total();
+    const MPoly *polys = static_cast<const MPoly *>(b_mesh.polygons[0].ptr.data);
+    for (int i = 0; i < polys_num; i++) {
+      const MPoly &b_poly = polys[i];
+      numngons += (b_poly.totloop == 4) ? 0 : 1;
+      numcorners += b_poly.totloop;
     }
   }
 
@@ -939,17 +982,23 @@ static void create_mesh(Scene *scene,
   mesh->reserve_mesh(numverts, numtris);
 
   /* create vertex coordinates and normals */
-  BL::Mesh::vertices_iterator v;
-  for (b_mesh.vertices.begin(v); v != b_mesh.vertices.end(); ++v)
-    mesh->add_vertex(get_float3(v->co()));
+  for (int i = 0; i < numverts; i++) {
+    const MVert &b_vert = verts[i];
+    mesh->add_vertex(make_float3(b_vert.co[0], b_vert.co[1], b_vert.co[2]));
+  }
 
   AttributeSet &attributes = (subdivision) ? mesh->subd_attributes : mesh->attributes;
   Attribute *attr_N = attributes.add(ATTR_STD_VERTEX_NORMAL);
   float3 *N = attr_N->data_float3();
 
-  for (b_mesh.vertices.begin(v); v != b_mesh.vertices.end(); ++v, ++N)
-    *N = get_float3(v->normal());
-  N = attr_N->data_float3();
+  if (subdivision || !use_loop_normals) {
+    const float(*b_vert_normals)[3] = static_cast<const float(*)[3]>(
+        b_mesh.vertex_normals[0].ptr.data);
+    for (int i = 0; i < numverts; i++) {
+      const float *b_vert_normal = b_vert_normals[i];
+      N[i] = make_float3(b_vert_normal[0], b_vert_normal[1], b_vert_normal[2]);
+    }
+  }
 
   /* create generated coordinates from undeformed coordinates */
   const bool need_default_tangent = (subdivision == false) && (b_mesh.uv_layers.empty()) &&
@@ -964,6 +1013,7 @@ static void create_mesh(Scene *scene,
     float3 *generated = attr->data_float3();
     size_t i = 0;
 
+    BL::Mesh::vertices_iterator v;
     for (b_mesh.vertices.begin(v); v != b_mesh.vertices.end(); ++v) {
       generated[i++] = get_float3(v->undeformed_co()) * size - loc;
     }
@@ -978,14 +1028,15 @@ static void create_mesh(Scene *scene,
   };
 
   /* create faces */
+  const MPoly *polys = static_cast<const MPoly *>(b_mesh.polygons[0].ptr.data);
   if (!subdivision) {
     for (BL::MeshLoopTriangle &t : b_mesh.loop_triangles) {
       const int poly_index = t.polygon_index();
-      BL::MeshPolygon p = b_mesh.polygons[poly_index];
+      const MPoly &b_poly = polys[poly_index];
       int3 vi = get_int3(t.vertices());
 
       int shader = get_material_index(poly_index);
-      bool smooth = p.use_smooth() || use_loop_normals;
+      bool smooth = (b_poly.flag & ME_SMOOTH) || use_loop_normals;
 
       if (use_loop_normals) {
         BL::Array<float, 9> loop_normals = t.split_normals();
@@ -1005,16 +1056,19 @@ static void create_mesh(Scene *scene,
   else {
     vector<int> vi;
 
-    for (int poly_index = 0; poly_index < numfaces; poly_index++) {
-      BL::MeshPolygon p = b_mesh.polygons[poly_index];
-      int n = p.loop_total();
-      int shader = get_material_index(poly_index);
-      bool smooth = p.use_smooth() || use_loop_normals;
+    const MLoop *loops = static_cast<const MLoop *>(b_mesh.loops[0].ptr.data);
+
+    for (int i = 0; i < numfaces; i++) {
+      const MPoly &b_poly = polys[i];
+      int n = b_poly.totloop;
+      int shader = get_material_index(i);
+      bool smooth = (b_poly.flag & ME_SMOOTH) || use_loop_normals;
 
       vi.resize(n);
       for (int i = 0; i < n; i++) {
         /* NOTE: Autosmooth is already taken care about. */
-        vi[i] = b_mesh.loops[p.loop_start() + i].vertex_index();
+
+        vi[i] = loops[b_poly.loopstart + i].v;
       }
 
       /* create subd faces */
@@ -1067,27 +1121,33 @@ static void create_subd_mesh(Scene *scene,
 
   create_mesh(scene, mesh, b_mesh, used_shaders, need_motion, motion_scale, true, subdivide_uvs);
 
-  /* export creases */
-  size_t num_creases = 0;
+  const int edges_num = b_mesh.edges.length();
+
+  if (edges_num != 0) {
+    size_t num_creases = 0;
+    const MEdge *edges = static_cast<MEdge *>(b_mesh.edges[0].ptr.data);
 
-  for (BL::MeshEdge &e : b_mesh.edges) {
-    if (e.crease() != 0.0f) {
-      num_creases++;
+    for (int i = 0; i < edges_num; i++) {
+      const MEdge &b_edge = edges[i];
+      if (b_edge.crease != 0) {
+        num_creases++;
+      }
     }
-  }
 
-  mesh->reserve_subd_creases(num_creases);
+    mesh->reserve_subd_creases(num_creases);
 
-  for (BL::MeshEdge &e : b_mesh.edges) {
-    if (e.crease() != 0.0f) {
-      mesh->add_edge_crease(e.vertices()[0], e.vertices()[1], e.crease());
+    for (int i = 0; i < edges_num; i++) {
+      const MEdge &b_edge = edges[i];
+      if (b_edge.crease != 0) {
+        mesh->add_edge_crease(b_edge.v1, b_edge.v2, float(b_edge.crease) / 255.0f);
+      }
     }
-  }
 
-  for (BL::MeshVertexCreaseLayer &c : b_mesh.vertex_creases) {
-    for (int i = 0; i < c.data.length(); ++i) {
-      if (c.data[i].value() != 0.0f) {
-        mesh->add_vertex_crease(i, c.data[i].value());
+    for (BL::MeshVertexCreaseLayer &c : b_mesh.vertex_creases) {
+      for (int i = 0; i < c.data.length(); ++i) {
+        if (c.data[i].value() != 0.0f) {
+          mesh->add_vertex_crease(i, c.data[i].value());
+        }
       }
     }
   }
@@ -1208,6 +1268,12 @@ void BlenderSync::sync_mesh_motion(BL::Depsgraph b_depsgraph,
 
   /* TODO(sergey): Perform preliminary check for number of vertices. */
   if (b_mesh) {
+    const int b_verts_num = b_mesh.vertices.length();
+    if (b_verts_num == 0) {
+      free_object_to_mesh(b_data, b_ob_info, b_mesh);
+      return;
+    }
+
     /* Export deformed coordinates. */
     /* Find attributes. */
     Attribute *attr_mP = mesh->attributes.find(ATTR_STD_MOTION_VERTEX_POSITION);
@@ -1225,22 +1291,30 @@ void BlenderSync::sync_mesh_motion(BL::Depsgraph b_depsgraph,
     /* Load vertex data from mesh. */
     float3 *mP = attr_mP->data_float3() + motion_step * numverts;
     float3 *mN = (attr_mN) ? attr_mN->data_float3() + motion_step * numverts : NULL;
+
+    const MVert *verts = static_cast<const MVert *>(b_mesh.vertices[0].ptr.data);
+
     /* NOTE: We don't copy more that existing amount of vertices to prevent
      * possible memory corruption.
      */
-    BL::Mesh::vertices_iterator v;
-    int i = 0;
-    for (b_mesh.vertices.begin(v); v != b_mesh.vertices.end() && i < numverts; ++v, ++i) {
-      mP[i] = get_float3(v->co());
-      if (mN)
-        mN[i] = get_float3(v->normal());
+    for (int i = 0; i < std::min<size_t>(b_verts_num, numverts); i++) {
+      const MVert &b_vert = verts[i];
+      mP[i] = make_float3(b_vert.co[0], b_vert.co[1], b_vert.co[2]);
+    }
+    if (mN) {
+      const float(*b_vert_normals)[3] = static_cast<const float(*)[3]>(
+          b_mesh.vertex_normals[0].ptr.data);
+      for (int i = 0; i < std::min<size_t>(b_verts_num, numverts); i++) {
+        const float *b_vert_normal = b_vert_normals[i];
+        mN[i] = make_float3(b_vert_normal[0], b_vert_normal[1], b_vert_normal[2]);
+      }
     }
     if (new_attribute) {
       /* In case of new attribute, we verify if there really was any motion. */
-      if (b_mesh.vertices.length() != numverts ||
+      if (b_verts_num != numverts ||
           memcmp(mP, &mesh->get_verts()[0], sizeof(float3) * numverts) == 0) {
         /* no motion, remove attributes again */
-        if (b_mesh.vertices.length() != numverts) {
+        if (b_verts_num != numverts) {
           VLOG_WARNING << "Topology differs, disabling motion blur for object " << ob_name;
         }
         else {
@@ -1264,7 +1338,7 @@ void BlenderSync::sync_mesh_motion(BL::Depsgraph b_depsgraph,
       }
     }
     else {
-      if (b_mesh.vertices.length() != numverts) {
+      if (b_verts_num != numverts) {
         VLOG_WARNING << "Topology differs, discarding motion blur for object " << ob_name
                      << " at time " << motion_step;
         memcpy(mP, &mesh->get_verts()[0], sizeof(float3) * numverts);