Mesh: Move selection flags to generic attributes

Using the attribute name semantics from T97452, this patch moves the
selection status of mesh elements from the `SELECT` of vertices, and
edges, and the `ME_FACE_SEL` of faces to generic boolean attribute
Storing this data as generic attributes can significantly simplify and
improve code, as described in T95965.

The attributes are called `.select_vert`, `.select_edge`, and
`.select_poly`. The `.` prefix means they are "UI attributes",so they
still contain original data edited by users, but they aren't meant to
be accessed procedurally by the user in arbitrary situations. They are
also be hidden in the spreadsheet and the attribute list.

Until 4.0, the attributes are still written to and read from the mesh
in the old way, so neither forward nor backward compatibility are
affected. This means memory requirements will be increased by one byte
per element when selection is used. When the flags are removed
completely, requirements will decrease.

Further notes:
* The `MVert` flag is empty at runtime now, so it can be ignored.
* `BMesh` is unchanged, otherwise the change would be much larger.
* Many tests have slightly different results, since the selection
  attribute uses more generic propagation. Previously you couldn't
  really rely on edit mode selections being propagated procedurally.
  Now it mostly works as expected.

Similar to 2480b55f216c
Ref T95965

Differential Revision: https://developer.blender.org/D15795

1 files changed, 56 insertions, 71 deletions

diff --git a/source/blender/blenkernel/intern/mesh_evaluate.cc b/source/blender/blenkernel/intern/mesh_evaluate.cc
index 938d7e42aa3..4f8391263a1 100644
--- a/source/blender/blenkernel/intern/mesh_evaluate.cc
+++ b/source/blender/blenkernel/intern/mesh_evaluate.cc
@@ -818,103 +818,88 @@ void BKE_mesh_flush_hidden_from_polys(Mesh *me)
   hide_edge.finish();
 }
 
-void BKE_mesh_flush_select_from_polys_ex(MVert *mvert,
-                                         const int totvert,
-                                         const MLoop *mloop,
-                                         MEdge *medge,
-                                         const int totedge,
-                                         const MPoly *mpoly,
-                                         const int totpoly)
+void BKE_mesh_flush_select_from_polys(Mesh *me)
 {
-  MVert *mv;
-  MEdge *med;
-  const MPoly *mp;
-
-  int i = totvert;
-  for (mv = mvert; i--; mv++) {
-    mv->flag &= (char)~SELECT;
+  using namespace blender::bke;
+  MutableAttributeAccessor attributes = me->attributes_for_write();
+  const VArray<bool> select_poly = attributes.lookup_or_default<bool>(
+      ".select_poly", ATTR_DOMAIN_FACE, false);
+  if (select_poly.is_single() && !select_poly.get_internal_single()) {
+    attributes.remove(".select_vert");
+    attributes.remove(".select_edge");
+    return;
   }
+  SpanAttributeWriter<bool> select_vert = attributes.lookup_or_add_for_write_only_span<bool>(
+      ".select_vert", ATTR_DOMAIN_POINT);
+  SpanAttributeWriter<bool> select_edge = attributes.lookup_or_add_for_write_only_span<bool>(
+      ".select_edge", ATTR_DOMAIN_EDGE);
 
-  i = totedge;
-  for (med = medge; i--; med++) {
-    med->flag &= ~SELECT;
-  }
+  /* Use generic domain interpolation to read the polygon attribute on the other domains.
+   * Assume selected faces are not hidden and none of their vertices/edges are hidden. */
+  attributes.lookup_or_default<bool>(".select_poly", ATTR_DOMAIN_POINT, false)
+      .materialize(select_vert.span);
+  attributes.lookup_or_default<bool>(".select_poly", ATTR_DOMAIN_EDGE, false)
+      .materialize(select_edge.span);
 
-  i = totpoly;
-  for (mp = mpoly; i--; mp++) {
-    /* Assume if its selected its not hidden and none of its verts/edges are hidden
-     * (a common assumption). */
-    if (mp->flag & ME_FACE_SEL) {
-      const MLoop *ml;
-      int j;
-      j = mp->totloop;
-      for (ml = &mloop[mp->loopstart]; j--; ml++) {
-        mvert[ml->v].flag |= SELECT;
-        medge[ml->e].flag |= SELECT;
-      }
-    }
-  }
-}
-void BKE_mesh_flush_select_from_polys(Mesh *me)
-{
-  BKE_mesh_flush_select_from_polys_ex(me->verts_for_write().data(),
-                                      me->totvert,
-                                      me->loops().data(),
-                                      me->edges_for_write().data(),
-                                      me->totedge,
-                                      me->polys().data(),
-                                      me->totpoly);
+  select_vert.finish();
+  select_edge.finish();
 }
 
-static void mesh_flush_select_from_verts(const Span<MVert> verts,
+static void mesh_flush_select_from_verts(const Span<MEdge> edges,
+                                         const Span<MPoly> polys,
                                          const Span<MLoop> loops,
                                          const VArray<bool> &hide_edge,
                                          const VArray<bool> &hide_poly,
-                                         MutableSpan<MEdge> edges,
-                                         MutableSpan<MPoly> polys)
+                                         const VArray<bool> &select_vert,
+                                         MutableSpan<bool> select_edge,
+                                         MutableSpan<bool> select_poly)
 {
+  /* Select visible edges that have both of their vertices selected. */
   for (const int i : edges.index_range()) {
     if (!hide_edge[i]) {
-      MEdge &edge = edges[i];
-      if ((verts[edge.v1].flag & SELECT) && (verts[edge.v2].flag & SELECT)) {
-        edge.flag |= SELECT;
-      }
-      else {
-        edge.flag &= ~SELECT;
-      }
+      const MEdge &edge = edges[i];
+      select_edge[i] = select_vert[edge.v1] && select_vert[edge.v2];
     }
   }
 
+  /* Select visible faces that have all of their vertices selected. */
   for (const int i : polys.index_range()) {
-    if (hide_poly[i]) {
-      continue;
-    }
-    MPoly &poly = polys[i];
-    bool all_verts_selected = true;
-    for (const MLoop &loop : loops.slice(poly.loopstart, poly.totloop)) {
-      if (!(verts[loop.v].flag & SELECT)) {
-        all_verts_selected = false;
-      }
-    }
-    if (all_verts_selected) {
-      poly.flag |= ME_FACE_SEL;
-    }
-    else {
-      poly.flag &= (char)~ME_FACE_SEL;
+    if (!hide_poly[i]) {
+      const MPoly &poly = polys[i];
+      const Span<MLoop> poly_loops = loops.slice(poly.loopstart, poly.totloop);
+      select_poly[i] = std::all_of(poly_loops.begin(), poly_loops.end(), [&](const MLoop &loop) {
+        return select_vert[loop.v];
+      });
     }
   }
 }
 
 void BKE_mesh_flush_select_from_verts(Mesh *me)
 {
-  const blender::bke::AttributeAccessor attributes = me->attributes();
+  using namespace blender::bke;
+  MutableAttributeAccessor attributes = me->attributes_for_write();
+  const VArray<bool> select_vert = attributes.lookup_or_default<bool>(
+      ".select_vert", ATTR_DOMAIN_POINT, false);
+  if (select_vert.is_single() && !select_vert.get_internal_single()) {
+    attributes.remove(".select_edge");
+    attributes.remove(".select_poly");
+    return;
+  }
+  SpanAttributeWriter<bool> select_edge = attributes.lookup_or_add_for_write_only_span<bool>(
+      ".select_edge", ATTR_DOMAIN_EDGE);
+  SpanAttributeWriter<bool> select_poly = attributes.lookup_or_add_for_write_only_span<bool>(
+      ".select_poly", ATTR_DOMAIN_FACE);
   mesh_flush_select_from_verts(
-      me->verts(),
+      me->edges(),
+      me->polys(),
       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->edges_for_write(),
-      me->polys_for_write());
+      select_vert,
+      select_edge.span,
+      select_poly.span);
+  select_edge.finish();
+  select_poly.finish();
 }
 
 /** \} */