Mesh: Move hide flags to generic attributes

This commit moves the hide status of mesh vertices, edges, and faces
from the `ME_FLAG` to optional generic boolean attributes. Storing this
data as generic attributes can significantly simplify and improve code,
as described in T95965.

The attributes are called `.hide_vert`, `.hide_edge`, and `.hide_poly`,
using the attribute name semantics discussed in T97452. 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 by default,

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 the hide status is used. When the flags are removed
completely, requirements will decrease when hiding is unused.

Further notes:
 * Some code can be further simplified to skip some processing when the
   hide attributes don't exist.
 * The data is still stored in flags for `BMesh`, necessitating some
   complexity in the conversion to and from `Mesh`.
 * Access to the "hide" property of mesh elements in RNA is slower.
   The separate boolean arrays should be used where possible.

Ref T95965

Differential Revision: https://developer.blender.org/D14685

1 files changed, 85 insertions, 63 deletions

diff --git a/source/blender/blenkernel/intern/mesh_evaluate.cc b/source/blender/blenkernel/intern/mesh_evaluate.cc
index 7d26262a504..ebe1f8852e4 100644
--- a/source/blender/blenkernel/intern/mesh_evaluate.cc
+++ b/source/blender/blenkernel/intern/mesh_evaluate.cc
@@ -22,15 +22,17 @@
 #include "BLI_math.h"
 #include "BLI_span.hh"
 #include "BLI_utildefines.h"
+#include "BLI_virtual_array.hh"
 
 #include "BKE_customdata.h"
 
+#include "BKE_attribute.hh"
 #include "BKE_mesh.h"
 #include "BKE_multires.h"
 
-using blender::IndexRange;
 using blender::MutableSpan;
 using blender::Span;
+using blender::VArray;
 
 /* -------------------------------------------------------------------- */
 /** \name Polygon Calculations
@@ -732,75 +734,89 @@ void BKE_mesh_polygons_flip(MPoly *mpoly, MLoop *mloop, CustomData *ldata, int t
 /** \name Mesh Flag Flushing
  * \{ */
 
-void BKE_mesh_flush_hidden_from_verts_ex(const MVert *mvert,
-                                         const MLoop *mloop,
-                                         MEdge *medge,
-                                         const int totedge,
-                                         MPoly *mpoly,
-                                         const int totpoly)
+void BKE_mesh_flush_hidden_from_verts(Mesh *me)
 {
-  int i, j;
+  using namespace blender;
+  using namespace blender::bke;
+  MutableAttributeAccessor attributes = mesh_attributes_for_write(*me);
 
-  for (i = 0; i < totedge; i++) {
-    MEdge *e = &medge[i];
-    if (mvert[e->v1].flag & ME_HIDE || mvert[e->v2].flag & ME_HIDE) {
-      e->flag |= ME_HIDE;
-    }
-    else {
-      e->flag &= ~ME_HIDE;
-    }
+  const VArray<bool> hide_vert = attributes.lookup_or_default<bool>(
+      ".hide_vert", ATTR_DOMAIN_POINT, false);
+  if (hide_vert.is_single() && !hide_vert.get_internal_single()) {
+    attributes.remove(".hide_edge");
+    attributes.remove(".hide_poly");
+    return;
   }
-  for (i = 0; i < totpoly; i++) {
-    MPoly *p = &mpoly[i];
-    p->flag &= (char)~ME_HIDE;
-    for (j = 0; j < p->totloop; j++) {
-      if (mvert[mloop[p->loopstart + j].v].flag & ME_HIDE) {
-        p->flag |= ME_HIDE;
-      }
-    }
+  const VArraySpan<bool> hide_vert_span{hide_vert};
+  const Span<MEdge> edges(me->medge, me->totedge);
+  const Span<MPoly> polys(me->mpoly, me->totpoly);
+  const Span<MLoop> loops(me->mloop, me->totloop);
+
+  /* Hide edges when either of their vertices are hidden. */
+  SpanAttributeWriter<bool> hide_edge = attributes.lookup_or_add_for_write_only_span<bool>(
+      ".hide_edge", ATTR_DOMAIN_EDGE);
+  for (const int i : edges.index_range()) {
+    const MEdge &edge = edges[i];
+    hide_edge.span[i] = hide_vert_span[edge.v1] || hide_vert_span[edge.v2];
   }
-}
-void BKE_mesh_flush_hidden_from_verts(Mesh *me)
-{
-  BKE_mesh_flush_hidden_from_verts_ex(
-      me->mvert, me->mloop, me->medge, me->totedge, me->mpoly, me->totpoly);
+  hide_edge.finish();
+
+  /* Hide faces when any of their vertices are hidden. */
+  SpanAttributeWriter<bool> hide_poly = attributes.lookup_or_add_for_write_only_span<bool>(
+      ".hide_poly", ATTR_DOMAIN_FACE);
+  for (const int i : polys.index_range()) {
+    const MPoly &poly = polys[i];
+    const Span<MLoop> loops = loops.slice(poly.loopstart, poly.totloop);
+    hide_poly.span[i] = std::any_of(
+        loops.begin(), loops.end(), [&](const MLoop &loop) { return hide_vert_span[loop.v]; });
+  }
+  hide_poly.finish();
 }
 
-void BKE_mesh_flush_hidden_from_polys_ex(MVert *mvert,
-                                         const MLoop *mloop,
-                                         MEdge *medge,
-                                         const int UNUSED(totedge),
-                                         const MPoly *mpoly,
-                                         const int totpoly)
+void BKE_mesh_flush_hidden_from_polys(Mesh *me)
 {
-  int i = totpoly;
-  for (const MPoly *mp = mpoly; i--; mp++) {
-    if (mp->flag & ME_HIDE) {
-      const MLoop *ml;
-      int j = mp->totloop;
-      for (ml = &mloop[mp->loopstart]; j--; ml++) {
-        mvert[ml->v].flag |= ME_HIDE;
-        medge[ml->e].flag |= ME_HIDE;
+  using namespace blender;
+  using namespace blender::bke;
+  MutableAttributeAccessor attributes = mesh_attributes_for_write(*me);
+
+  const VArray<bool> hide_poly = attributes.lookup_or_default<bool>(
+      ".hide_poly", ATTR_DOMAIN_FACE, false);
+  if (hide_poly.is_single() && !hide_poly.get_internal_single()) {
+    attributes.remove(".hide_vert");
+    attributes.remove(".hide_edge");
+    return;
+  }
+  const VArraySpan<bool> hide_face_span{hide_poly};
+  const Span<MPoly> polys(me->mpoly, me->totpoly);
+  const Span<MLoop> loops(me->mloop, me->totloop);
+  SpanAttributeWriter<bool> hide_vert = attributes.lookup_or_add_for_write_only_span<bool>(
+      ".hide_vert", ATTR_DOMAIN_POINT);
+  SpanAttributeWriter<bool> hide_edge = attributes.lookup_or_add_for_write_only_span<bool>(
+      ".hide_edge", ATTR_DOMAIN_EDGE);
+
+  /* Hide all edges or vertices connected to hidden faces. */
+  for (const int i : polys.index_range()) {
+    if (hide_face_span[i]) {
+      const MPoly &poly = polys[i];
+      for (const MLoop &loop : loops.slice(poly.loopstart, poly.totloop)) {
+        hide_vert.span[loop.v] = true;
+        hide_edge.span[loop.e] = true;
       }
     }
   }
-
-  i = totpoly;
-  for (const MPoly *mp = mpoly; i--; mp++) {
-    if ((mp->flag & ME_HIDE) == 0) {
-      const MLoop *ml;
-      int j = mp->totloop;
-      for (ml = &mloop[mp->loopstart]; j--; ml++) {
-        mvert[ml->v].flag &= (char)~ME_HIDE;
-        medge[ml->e].flag &= (short)~ME_HIDE;
+  /* Unhide vertices and edges connected to visible faces. */
+  for (const int i : polys.index_range()) {
+    if (!hide_face_span[i]) {
+      const MPoly &poly = polys[i];
+      for (const MLoop &loop : loops.slice(poly.loopstart, poly.totloop)) {
+        hide_vert.span[loop.v] = false;
+        hide_edge.span[loop.e] = false;
       }
     }
   }
-}
-void BKE_mesh_flush_hidden_from_polys(Mesh *me)
-{
-  BKE_mesh_flush_hidden_from_polys_ex(
-      me->mvert, me->mloop, me->medge, me->totedge, me->mpoly, me->totpoly);
+
+  hide_vert.finish();
+  hide_edge.finish();
 }
 
 void BKE_mesh_flush_select_from_polys_ex(MVert *mvert,
@@ -848,11 +864,13 @@ void BKE_mesh_flush_select_from_polys(Mesh *me)
 
 static void mesh_flush_select_from_verts(const Span<MVert> verts,
                                          const Span<MLoop> loops,
+                                         const VArray<bool> &hide_edge,
+                                         const VArray<bool> &hide_poly,
                                          MutableSpan<MEdge> edges,
                                          MutableSpan<MPoly> polys)
 {
   for (const int i : edges.index_range()) {
-    if ((edges[i].flag & ME_HIDE) == 0) {
+    if (!hide_edge[i]) {
       MEdge &edge = edges[i];
       if ((verts[edge.v1].flag & SELECT) && (verts[edge.v2].flag & SELECT)) {
         edge.flag |= SELECT;
@@ -864,7 +882,7 @@ static void mesh_flush_select_from_verts(const Span<MVert> verts,
   }
 
   for (const int i : polys.index_range()) {
-    if (polys[i].flag & ME_HIDE) {
+    if (hide_poly[i]) {
       continue;
     }
     MPoly &poly = polys[i];
@@ -885,10 +903,14 @@ static void mesh_flush_select_from_verts(const Span<MVert> verts,
 
 void BKE_mesh_flush_select_from_verts(Mesh *me)
 {
-  mesh_flush_select_from_verts({me->mvert, me->totvert},
-                               {me->mloop, me->totloop},
-                               {me->medge, me->totedge},
-                               {me->mpoly, me->totpoly});
+  const blender::bke::AttributeAccessor attributes = blender::bke::mesh_attributes(*me);
+  mesh_flush_select_from_verts(
+      {me->mvert, me->totvert},
+      {me->mloop, me->totloop},
+      attributes.lookup_or_default<bool>(".hide_edge", ATTR_DOMAIN_EDGE, false),
+      attributes.lookup_or_default<bool>(".hide_poly", ATTR_DOMAIN_FACE, false),
+      {me->medge, me->totedge},
+      {me->mpoly, me->totpoly});
 }
 
 /** \} */