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, 33 deletions

diff --git a/source/blender/editors/curves/intern/curves_ops.cc b/source/blender/editors/curves/intern/curves_ops.cc
index eec2c5d205d..6582ce6e6d7 100644
--- a/source/blender/editors/curves/intern/curves_ops.cc
+++ b/source/blender/editors/curves/intern/curves_ops.cc
@@ -139,7 +139,8 @@ using bke::CurvesGeometry;
 
 namespace convert_to_particle_system {
 
-static int find_mface_for_root_position(const Mesh &mesh,
+static int find_mface_for_root_position(const Span<MVert> verts,
+                                        const MFace *mface,
                                         const Span<int> possible_mface_indices,
                                         const float3 &root_pos)
 {
@@ -151,14 +152,14 @@ static int find_mface_for_root_position(const Mesh &mesh,
   int mface_i;
   float best_distance_sq = FLT_MAX;
   for (const int possible_mface_i : possible_mface_indices) {
-    const MFace &possible_mface = mesh.mface[possible_mface_i];
+    const MFace &possible_mface = mface[possible_mface_i];
     {
       float3 point_in_triangle;
       closest_on_tri_to_point_v3(point_in_triangle,
                                  root_pos,
-                                 mesh.mvert[possible_mface.v1].co,
-                                 mesh.mvert[possible_mface.v2].co,
-                                 mesh.mvert[possible_mface.v3].co);
+                                 verts[possible_mface.v1].co,
+                                 verts[possible_mface.v2].co,
+                                 verts[possible_mface.v3].co);
       const float distance_sq = len_squared_v3v3(root_pos, point_in_triangle);
       if (distance_sq < best_distance_sq) {
         best_distance_sq = distance_sq;
@@ -170,9 +171,9 @@ static int find_mface_for_root_position(const Mesh &mesh,
       float3 point_in_triangle;
       closest_on_tri_to_point_v3(point_in_triangle,
                                  root_pos,
-                                 mesh.mvert[possible_mface.v1].co,
-                                 mesh.mvert[possible_mface.v3].co,
-                                 mesh.mvert[possible_mface.v4].co);
+                                 verts[possible_mface.v1].co,
+                                 verts[possible_mface.v3].co,
+                                 verts[possible_mface.v4].co);
       const float distance_sq = len_squared_v3v3(root_pos, point_in_triangle);
       if (distance_sq < best_distance_sq) {
         best_distance_sq = distance_sq;
@@ -186,25 +187,22 @@ static int find_mface_for_root_position(const Mesh &mesh,
 /**
  * \return Barycentric coordinates in the #MFace.
  */
-static float4 compute_mface_weights_for_position(const Mesh &mesh,
+static float4 compute_mface_weights_for_position(const Span<MVert> verts,
                                                  const MFace &mface,
                                                  const float3 &position)
 {
   float4 mface_weights;
   if (mface.v4) {
     float mface_verts_su[4][3];
-    copy_v3_v3(mface_verts_su[0], mesh.mvert[mface.v1].co);
-    copy_v3_v3(mface_verts_su[1], mesh.mvert[mface.v2].co);
-    copy_v3_v3(mface_verts_su[2], mesh.mvert[mface.v3].co);
-    copy_v3_v3(mface_verts_su[3], mesh.mvert[mface.v4].co);
+    copy_v3_v3(mface_verts_su[0], verts[mface.v1].co);
+    copy_v3_v3(mface_verts_su[1], verts[mface.v2].co);
+    copy_v3_v3(mface_verts_su[2], verts[mface.v3].co);
+    copy_v3_v3(mface_verts_su[3], verts[mface.v4].co);
     interp_weights_poly_v3(mface_weights, mface_verts_su, 4, position);
   }
   else {
-    interp_weights_tri_v3(mface_weights,
-                          mesh.mvert[mface.v1].co,
-                          mesh.mvert[mface.v2].co,
-                          mesh.mvert[mface.v3].co,
-                          position);
+    interp_weights_tri_v3(
+        mface_weights, verts[mface.v1].co, verts[mface.v2].co, verts[mface.v3].co, position);
     mface_weights[3] = 0.0f;
   }
   return mface_weights;
@@ -287,6 +285,9 @@ static void try_convert_single_object(Object &curves_ob,
   /* Prepare transformation matrices. */
   const bke::CurvesSurfaceTransforms transforms{curves_ob, &surface_ob};
 
+  const MFace *mfaces = (const MFace *)CustomData_get_layer(&surface_me.fdata, CD_MFACE);
+  const Span<MVert> verts = surface_me.vertices();
+
   for (const int new_hair_i : IndexRange(hair_num)) {
     const int curve_i = new_hair_i;
     const IndexRange points = curves.points_for_curve(curve_i);
@@ -305,11 +306,10 @@ static void try_convert_single_object(Object &curves_ob,
     const int poly_i = looptri.poly;
 
     const int mface_i = find_mface_for_root_position(
-        surface_me, poly_to_mface_map[poly_i], root_pos_su);
-    const MFace &mface = surface_me.mface[mface_i];
+        verts, mfaces, poly_to_mface_map[poly_i], root_pos_su);
+    const MFace &mface = mfaces[mface_i];
 
-    const float4 mface_weights = compute_mface_weights_for_position(
-        surface_me, mface, root_pos_su);
+    const float4 mface_weights = compute_mface_weights_for_position(verts, mface, root_pos_su);
 
     ParticleData &particle = particles[new_hair_i];
     const int num_keys = points.size();
@@ -541,8 +541,11 @@ static void snap_curves_to_surface_exec_object(Object &curves_ob,
   Curves &curves_id = *static_cast<Curves *>(curves_ob.data);
   CurvesGeometry &curves = CurvesGeometry::wrap(curves_id.geometry);
 
-  Mesh &surface_mesh = *static_cast<Mesh *>(surface_ob.data);
-
+  const Mesh &surface_mesh = *static_cast<const Mesh *>(surface_ob.data);
+  const Span<MVert> verts = surface_mesh.vertices();
+  const Span<MLoop> loops = surface_mesh.loops();
+  const Span<MLoopTri> surface_looptris = {BKE_mesh_runtime_looptri_ensure(&surface_mesh),
+                                           BKE_mesh_runtime_looptri_len(&surface_mesh)};
   VArraySpan<float2> surface_uv_map;
   if (curves_id.surface_uv_map != nullptr) {
     const bke::AttributeAccessor surface_attributes = bke::mesh_attributes(surface_mesh);
@@ -554,9 +557,6 @@ static void snap_curves_to_surface_exec_object(Object &curves_ob,
   MutableSpan<float3> positions_cu = curves.positions_for_write();
   MutableSpan<float2> surface_uv_coords = curves.surface_uv_coords_for_write();
 
-  const Span<MLoopTri> surface_looptris = {BKE_mesh_runtime_looptri_ensure(&surface_mesh),
-                                           BKE_mesh_runtime_looptri_len(&surface_mesh)};
-
   const bke::CurvesSurfaceTransforms transforms{curves_ob, &surface_ob};
 
   switch (attach_mode) {
@@ -603,9 +603,9 @@ static void snap_curves_to_surface_exec_object(Object &curves_ob,
             const float2 &uv0 = surface_uv_map[corner0];
             const float2 &uv1 = surface_uv_map[corner1];
             const float2 &uv2 = surface_uv_map[corner2];
-            const float3 &p0_su = surface_mesh.mvert[surface_mesh.mloop[corner0].v].co;
-            const float3 &p1_su = surface_mesh.mvert[surface_mesh.mloop[corner1].v].co;
-            const float3 &p2_su = surface_mesh.mvert[surface_mesh.mloop[corner2].v].co;
+            const float3 &p0_su = verts[loops[corner0].v].co;
+            const float3 &p1_su = verts[loops[corner1].v].co;
+            const float3 &p2_su = verts[loops[corner2].v].co;
             float3 bary_coords;
             interp_weights_tri_v3(bary_coords, p0_su, p1_su, p2_su, new_first_point_pos_su);
             const float2 uv = attribute_math::mix3(bary_coords, uv0, uv1, uv2);
@@ -639,9 +639,9 @@ static void snap_curves_to_surface_exec_object(Object &curves_ob,
           const MLoopTri &looptri = *lookup_result.looptri;
           const float3 &bary_coords = lookup_result.bary_weights;
 
-          const float3 &p0_su = surface_mesh.mvert[surface_mesh.mloop[looptri.tri[0]].v].co;
-          const float3 &p1_su = surface_mesh.mvert[surface_mesh.mloop[looptri.tri[1]].v].co;
-          const float3 &p2_su = surface_mesh.mvert[surface_mesh.mloop[looptri.tri[2]].v].co;
+          const float3 &p0_su = verts[loops[looptri.tri[0]].v].co;
+          const float3 &p1_su = verts[loops[looptri.tri[1]].v].co;
+          const float3 &p2_su = verts[loops[looptri.tri[2]].v].co;
 
           float3 new_first_point_pos_su;
           interp_v3_v3v3v3(new_first_point_pos_su, p0_su, p1_su, p2_su, bary_coords);