Weight Paint: use coordinates from normal evaluated mesh if same topology.

Weight and Vertex paint don't change coordinates and thus don't need
crazyspace data, which allows using coordinates from normal evaluated
meshes.

Since painting uses original topology, the deform only mesh is used,
but if the fully evaluated mesh has the same topology, it is preferred.
This is useful because not only Geometry Nodes, but even simple weight
computation modifiers are excluded from the deform only mesh evaluation.

Differential Revision: https://developer.blender.org/D15501

1 files changed, 26 insertions, 8 deletions

diff --git a/source/blender/blenkernel/intern/paint.cc b/source/blender/blenkernel/intern/paint.cc
index 8c3f3d7bedc..a6b0a4d96ee 100644
--- a/source/blender/blenkernel/intern/paint.cc
+++ b/source/blender/blenkernel/intern/paint.cc
@@ -1616,7 +1616,7 @@ static bool sculpt_modifiers_active(Scene *scene, Sculpt *sd, Object *ob)
  */
 static void sculpt_update_object(Depsgraph *depsgraph,
                                  Object *ob,
-                                 Mesh *me_eval,
+                                 Object *ob_eval,
                                  bool need_pmap,
                                  bool need_mask,
                                  bool is_paint_tool)
@@ -1625,9 +1625,12 @@ static void sculpt_update_object(Depsgraph *depsgraph,
   Sculpt *sd = scene->toolsettings->sculpt;
   SculptSession *ss = ob->sculpt;
   const Mesh *me = BKE_object_get_original_mesh(ob);
+  Mesh *me_eval = BKE_object_get_evaluated_mesh(ob_eval);
   MultiresModifierData *mmd = BKE_sculpt_multires_active(scene, ob);
   const bool use_face_sets = (ob->mode & OB_MODE_SCULPT) != 0;
 
+  BLI_assert(me_eval != nullptr);
+
   ss->depsgraph = depsgraph;
 
   ss->deform_modifiers_active = sculpt_modifiers_active(scene, sd, ob);
@@ -1733,7 +1736,26 @@ static void sculpt_update_object(Depsgraph *depsgraph,
   pbvh_show_face_sets_set(ss->pbvh, ss->show_face_sets);
 
   if (ss->deform_modifiers_active) {
-    if (!ss->orig_cos) {
+    /* Painting doesn't need crazyspace, use already evaluated mesh coordinates. */
+    if (ob->mode & (OB_MODE_VERTEX_PAINT | OB_MODE_WEIGHT_PAINT)) {
+      Mesh *me_eval_deform = ob_eval->runtime.mesh_deform_eval;
+
+      /* If the fully evaluated mesh has the same topology as the deform-only version, use it.
+       * This matters because 'deform eval' is very restrictive and excludes even modifiers that
+       * simply recompute vertex weights. */
+      if (me_eval_deform->mpoly == me_eval->mpoly && me_eval_deform->mloop == me_eval->mloop &&
+          me_eval_deform->totvert == me_eval->totvert) {
+        me_eval_deform = me_eval;
+      }
+
+      BKE_sculptsession_free_deformMats(ss);
+
+      BLI_assert(me_eval_deform->totvert == me->totvert);
+
+      ss->deform_cos = BKE_mesh_vert_coords_alloc(me_eval_deform, NULL);
+      BKE_pbvh_vert_coords_apply(ss->pbvh, ss->deform_cos, me->totvert);
+    }
+    else if (!ss->orig_cos) {
       int a;
 
       BKE_sculptsession_free_deformMats(ss);
@@ -1871,10 +1893,8 @@ void BKE_sculpt_update_object_after_eval(Depsgraph *depsgraph, Object *ob_eval)
   /* Update after mesh evaluation in the dependency graph, to rebuild PBVH or
    * other data when modifiers change the mesh. */
   Object *ob_orig = DEG_get_original_object(ob_eval);
-  Mesh *me_eval = BKE_object_get_evaluated_mesh(ob_eval);
 
-  BLI_assert(me_eval != nullptr);
-  sculpt_update_object(depsgraph, ob_orig, me_eval, false, false, false);
+  sculpt_update_object(depsgraph, ob_orig, ob_eval, false, false, false);
 }
 
 void BKE_sculpt_color_layer_create_if_needed(Object *object)
@@ -1917,10 +1937,8 @@ void BKE_sculpt_update_object_for_edit(
   BLI_assert(ob_orig == DEG_get_original_object(ob_orig));
 
   Object *ob_eval = DEG_get_evaluated_object(depsgraph, ob_orig);
-  Mesh *me_eval = BKE_object_get_evaluated_mesh(ob_eval);
-  BLI_assert(me_eval != nullptr);
 
-  sculpt_update_object(depsgraph, ob_orig, me_eval, need_pmap, need_mask, is_paint_tool);
+  sculpt_update_object(depsgraph, ob_orig, ob_eval, need_pmap, need_mask, is_paint_tool);
 }
 
 int BKE_sculpt_mask_layers_ensure(Object *ob, MultiresModifierData *mmd)