Attributes: Improve custom data initialization options

When allocating new `CustomData` layers, often we do redundant
initialization of arrays. For example, it's common that values are
allocated, set to their default value, and then set to some other
value. This is wasteful, and it negates the benefits of optimizations
to the allocator like D15082. There are two reasons for this. The
first is array-of-structs storage that makes it annoying to initialize
values manually, and the second is confusing options in the Custom Data
API. This patch addresses the latter.

The `CustomData` "alloc type" options are rearranged. Now, besides
the options that use existing layers, there are two remaining:
* `CD_SET_DEFAULT` sets the default value.
  * Usually zeroes, but for colors this is white (how it was before).
  * Should be used when you add the layer but don't set all values.
* `CD_CONSTRUCT` refers to the "default construct" C++ term.
  * Only necessary or defined for non-trivial types like vertex groups.
  * Doesn't do anything for trivial types like `int` or `float3`.
  * Should be used every other time, when all values will be set.

The attribute API's `AttributeInit` types are updated as well.
To update code, replace `CD_CALLOC` with `CD_SET_DEFAULT` and
`CD_DEFAULT` with `CD_CONSTRUCT`. This doesn't cause any functional
changes yet. Follow-up commits will change to avoid initializing
new layers where the correctness is clear.

Differential Revision: https://developer.blender.org/D15617

2 files changed, 22 insertions, 21 deletions

diff --git a/source/blender/editors/mesh/mesh_data.cc b/source/blender/editors/mesh/mesh_data.cc
index ea29d07feaf..e394f8a7251 100644
--- a/source/blender/editors/mesh/mesh_data.cc
+++ b/source/blender/editors/mesh/mesh_data.cc
@@ -286,7 +286,8 @@ int ED_mesh_uv_add(
       is_init = true;
     }
     else {
-      CustomData_add_layer_named(&me->ldata, CD_MLOOPUV, CD_DEFAULT, nullptr, me->totloop, name);
+      CustomData_add_layer_named(
+          &me->ldata, CD_MLOOPUV, CD_SET_DEFAULT, nullptr, me->totloop, name);
     }
 
     if (active_set || layernum_dst == 0) {
@@ -409,7 +410,7 @@ int ED_mesh_color_add(
     }
     else {
       CustomData_add_layer_named(
-          &me->ldata, CD_PROP_BYTE_COLOR, CD_DEFAULT, nullptr, me->totloop, name);
+          &me->ldata, CD_PROP_BYTE_COLOR, CD_SET_DEFAULT, nullptr, me->totloop, name);
     }
 
     if (active_set || layernum == 0) {
@@ -432,7 +433,7 @@ bool ED_mesh_color_ensure(Mesh *me, const char *name)
 
   if (!layer) {
     CustomData_add_layer_named(
-        &me->ldata, CD_PROP_BYTE_COLOR, CD_DEFAULT, nullptr, me->totloop, name);
+        &me->ldata, CD_PROP_BYTE_COLOR, CD_SET_DEFAULT, nullptr, me->totloop, name);
     layer = me->ldata.layers + CustomData_get_layer_index(&me->ldata, CD_PROP_BYTE_COLOR);
 
     BKE_id_attributes_active_color_set(&me->id, layer);
@@ -500,7 +501,7 @@ int ED_mesh_sculpt_color_add(Mesh *me, const char *name, const bool do_init, Rep
     }
     else {
       CustomData_add_layer_named(
-          &me->vdata, CD_PROP_COLOR, CD_DEFAULT, nullptr, me->totvert, name);
+          &me->vdata, CD_PROP_COLOR, CD_SET_DEFAULT, nullptr, me->totvert, name);
     }
 
     if (layernum == 0) {
@@ -790,7 +791,7 @@ static int mesh_customdata_custom_splitnormals_add_exec(bContext *C, wmOperator
                                        me->smoothresh);
       }
 
-      CustomData_add_layer(data, CD_CUSTOMLOOPNORMAL, CD_DEFAULT, nullptr, me->totloop);
+      CustomData_add_layer(data, CD_CUSTOMLOOPNORMAL, CD_SET_DEFAULT, nullptr, me->totloop);
     }
 
     DEG_id_tag_update(&me->id, 0);
@@ -875,11 +876,11 @@ static void mesh_add_verts(Mesh *mesh, int len)
 
   int totvert = mesh->totvert + len;
   CustomData vdata;
-  CustomData_copy(&mesh->vdata, &vdata, CD_MASK_MESH.vmask, CD_DEFAULT, totvert);
+  CustomData_copy(&mesh->vdata, &vdata, CD_MASK_MESH.vmask, CD_SET_DEFAULT, totvert);
   CustomData_copy_data(&mesh->vdata, &vdata, 0, 0, mesh->totvert);
 
   if (!CustomData_has_layer(&vdata, CD_MVERT)) {
-    CustomData_add_layer(&vdata, CD_MVERT, CD_CALLOC, nullptr, totvert);
+    CustomData_add_layer(&vdata, CD_MVERT, CD_SET_DEFAULT, nullptr, totvert);
   }
 
   CustomData_free(&mesh->vdata, mesh->totvert);
@@ -913,11 +914,11 @@ static void mesh_add_edges(Mesh *mesh, int len)
   totedge = mesh->totedge + len;
 
   /* Update custom-data. */
-  CustomData_copy(&mesh->edata, &edata, CD_MASK_MESH.emask, CD_DEFAULT, totedge);
+  CustomData_copy(&mesh->edata, &edata, CD_MASK_MESH.emask, CD_SET_DEFAULT, totedge);
   CustomData_copy_data(&mesh->edata, &edata, 0, 0, mesh->totedge);
 
   if (!CustomData_has_layer(&edata, CD_MEDGE)) {
-    CustomData_add_layer(&edata, CD_MEDGE, CD_CALLOC, nullptr, totedge);
+    CustomData_add_layer(&edata, CD_MEDGE, CD_SET_DEFAULT, nullptr, totedge);
   }
 
   CustomData_free(&mesh->edata, mesh->totedge);
@@ -947,11 +948,11 @@ static void mesh_add_loops(Mesh *mesh, int len)
   totloop = mesh->totloop + len; /* new face count */
 
   /* update customdata */
-  CustomData_copy(&mesh->ldata, &ldata, CD_MASK_MESH.lmask, CD_DEFAULT, totloop);
+  CustomData_copy(&mesh->ldata, &ldata, CD_MASK_MESH.lmask, CD_SET_DEFAULT, totloop);
   CustomData_copy_data(&mesh->ldata, &ldata, 0, 0, mesh->totloop);
 
   if (!CustomData_has_layer(&ldata, CD_MLOOP)) {
-    CustomData_add_layer(&ldata, CD_MLOOP, CD_CALLOC, nullptr, totloop);
+    CustomData_add_layer(&ldata, CD_MLOOP, CD_SET_DEFAULT, nullptr, totloop);
   }
 
   BKE_mesh_runtime_clear_cache(mesh);
@@ -976,11 +977,11 @@ static void mesh_add_polys(Mesh *mesh, int len)
   totpoly = mesh->totpoly + len; /* new face count */
 
   /* update customdata */
-  CustomData_copy(&mesh->pdata, &pdata, CD_MASK_MESH.pmask, CD_DEFAULT, totpoly);
+  CustomData_copy(&mesh->pdata, &pdata, CD_MASK_MESH.pmask, CD_SET_DEFAULT, totpoly);
   CustomData_copy_data(&mesh->pdata, &pdata, 0, 0, mesh->totpoly);
 
   if (!CustomData_has_layer(&pdata, CD_MPOLY)) {
-    CustomData_add_layer(&pdata, CD_MPOLY, CD_CALLOC, nullptr, totpoly);
+    CustomData_add_layer(&pdata, CD_MPOLY, CD_SET_DEFAULT, nullptr, totpoly);
   }
 
   CustomData_free(&mesh->pdata, mesh->totpoly);
diff --git a/source/blender/editors/mesh/meshtools.cc b/source/blender/editors/mesh/meshtools.cc
index b1004b23a21..e9a34cf95cb 100644
--- a/source/blender/editors/mesh/meshtools.cc
+++ b/source/blender/editors/mesh/meshtools.cc
@@ -100,7 +100,7 @@ static void join_mesh_single(Depsgraph *depsgraph,
     ((Mesh *)ob_dst->data)->cd_flag |= me->cd_flag;
 
     /* standard data */
-    CustomData_merge(&me->vdata, vdata, CD_MASK_MESH.vmask, CD_DEFAULT, totvert);
+    CustomData_merge(&me->vdata, vdata, CD_MASK_MESH.vmask, CD_SET_DEFAULT, totvert);
     CustomData_copy_data_named(&me->vdata, vdata, 0, *vertofs, me->totvert);
 
     /* vertex groups */
@@ -199,7 +199,7 @@ static void join_mesh_single(Depsgraph *depsgraph,
   }
 
   if (me->totedge) {
-    CustomData_merge(&me->edata, edata, CD_MASK_MESH.emask, CD_DEFAULT, totedge);
+    CustomData_merge(&me->edata, edata, CD_MASK_MESH.emask, CD_SET_DEFAULT, totedge);
     CustomData_copy_data_named(&me->edata, edata, 0, *edgeofs, me->totedge);
 
     for (a = 0; a < me->totedge; a++, medge++) {
@@ -220,7 +220,7 @@ static void join_mesh_single(Depsgraph *depsgraph,
       }
     }
 
-    CustomData_merge(&me->ldata, ldata, CD_MASK_MESH.lmask, CD_DEFAULT, totloop);
+    CustomData_merge(&me->ldata, ldata, CD_MASK_MESH.lmask, CD_SET_DEFAULT, totloop);
     CustomData_copy_data_named(&me->ldata, ldata, 0, *loopofs, me->totloop);
 
     for (a = 0; a < me->totloop; a++, mloop++) {
@@ -244,7 +244,7 @@ static void join_mesh_single(Depsgraph *depsgraph,
       }
     }
 
-    CustomData_merge(&me->pdata, pdata, CD_MASK_MESH.pmask, CD_DEFAULT, totpoly);
+    CustomData_merge(&me->pdata, pdata, CD_MASK_MESH.pmask, CD_SET_DEFAULT, totpoly);
     CustomData_copy_data_named(&me->pdata, pdata, 0, *polyofs, me->totpoly);
 
     for (a = 0; a < me->totpoly; a++, mpoly++) {
@@ -571,10 +571,10 @@ int ED_mesh_join_objects_exec(bContext *C, wmOperator *op)
   CustomData_reset(&ldata);
   CustomData_reset(&pdata);
 
-  mvert = (MVert *)CustomData_add_layer(&vdata, CD_MVERT, CD_CALLOC, nullptr, totvert);
-  medge = (MEdge *)CustomData_add_layer(&edata, CD_MEDGE, CD_CALLOC, nullptr, totedge);
-  mloop = (MLoop *)CustomData_add_layer(&ldata, CD_MLOOP, CD_CALLOC, nullptr, totloop);
-  mpoly = (MPoly *)CustomData_add_layer(&pdata, CD_MPOLY, CD_CALLOC, nullptr, totpoly);
+  mvert = (MVert *)CustomData_add_layer(&vdata, CD_MVERT, CD_SET_DEFAULT, nullptr, totvert);
+  medge = (MEdge *)CustomData_add_layer(&edata, CD_MEDGE, CD_SET_DEFAULT, nullptr, totedge);
+  mloop = (MLoop *)CustomData_add_layer(&ldata, CD_MLOOP, CD_SET_DEFAULT, nullptr, totloop);
+  mpoly = (MPoly *)CustomData_add_layer(&pdata, CD_MPOLY, CD_SET_DEFAULT, nullptr, totpoly);
 
   vertofs = 0;
   edgeofs = 0;