Voxel Remesh: Fix poles and preserve volume

This commit fixes most of the issues we currently have in the voxel remesher. Mesh volume is preserved when doing multiple iterations, so the sculpt won't shrink and smooth each time you run the remesher. Mesh topology is much better, fixing most issues related to mask extraction and other topology based operations.

Reviewed By: jbakker

Differential Revision: https://developer.blender.org/D5863

1 files changed, 106 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/mesh_remesh_voxel.c b/source/blender/blenkernel/intern/mesh_remesh_voxel.c
index ff7ff947e1d..92e180601d7 100644
--- a/source/blender/blenkernel/intern/mesh_remesh_voxel.c
+++ b/source/blender/blenkernel/intern/mesh_remesh_voxel.c
@@ -38,6 +38,7 @@
 #include "DNA_mesh_types.h"
 #include "DNA_meshdata_types.h"
 
+#include "BKE_editmesh.h"
 #include "BKE_mesh.h"
 #include "BKE_mesh_runtime.h"
 #include "BKE_library.h"
@@ -45,6 +46,8 @@
 #include "BKE_bvhutils.h"
 #include "BKE_mesh_remesh_voxel.h" /* own include */
 
+#include "bmesh_tools.h"
+
 #ifdef WITH_OPENVDB
 #  include "openvdb_capi.h"
 #endif
@@ -348,3 +351,106 @@ void BKE_remesh_reproject_paint_mask(Mesh *target, Mesh *source)
   }
   free_bvhtree_from_mesh(&bvhtree);
 }
+
+struct Mesh *BKE_mesh_remesh_voxel_fix_poles(struct Mesh *mesh)
+{
+  const BMAllocTemplate allocsize = BMALLOC_TEMPLATE_FROM_ME(mesh);
+  BMesh *bm;
+  bm = BM_mesh_create(&allocsize,
+                      &((struct BMeshCreateParams){
+                          .use_toolflags = true,
+                      }));
+
+  BM_mesh_bm_from_me(bm,
+                     mesh,
+                     (&(struct BMeshFromMeshParams){
+                         .calc_face_normal = true,
+                     }));
+
+  BMVert *v;
+  BMEdge *ed, *ed_next;
+  BMFace *f, *f_next;
+  BMIter iter_a, iter_b;
+
+  /* Merge 3 edge poles vertices that exist in the same face */
+  BM_mesh_elem_hflag_disable_all(bm, BM_VERT | BM_EDGE | BM_FACE, BM_ELEM_TAG, false);
+  BM_ITER_MESH_MUTABLE (f, f_next, &iter_a, bm, BM_FACES_OF_MESH) {
+    BMVert *v1, *v2;
+    v1 = NULL;
+    v2 = NULL;
+    BM_ITER_ELEM (v, &iter_b, f, BM_VERTS_OF_FACE) {
+      if (BM_vert_edge_count(v) == 3) {
+        if (v1) {
+          v2 = v;
+        }
+        else {
+          v1 = v;
+        }
+      }
+    }
+    if (v1 && v2 && (v1 != v2) && !BM_edge_exists(v1, v2)) {
+      BM_face_kill(bm, f);
+      BMEdge *e = BM_edge_create(bm, v1, v2, NULL, BM_CREATE_NOP);
+      BM_elem_flag_set(e, BM_ELEM_TAG, true);
+    }
+  }
+
+  BM_ITER_MESH_MUTABLE (ed, ed_next, &iter_a, bm, BM_EDGES_OF_MESH) {
+    if (BM_elem_flag_test(ed, BM_ELEM_TAG)) {
+      float co[3];
+      mid_v3_v3v3(co, ed->v1->co, ed->v2->co);
+      BMVert *vc = BM_edge_collapse(bm, ed, ed->v1, true, true);
+      copy_v3_v3(vc->co, co);
+    }
+  }
+
+  /* Delete faces with a 3 edge pole in all their vertices */
+  BM_mesh_elem_hflag_disable_all(bm, BM_VERT | BM_EDGE | BM_FACE, BM_ELEM_TAG, false);
+  BM_ITER_MESH (f, &iter_a, bm, BM_FACES_OF_MESH) {
+    bool dissolve = true;
+    BM_ITER_ELEM (v, &iter_b, f, BM_VERTS_OF_FACE) {
+      if (BM_vert_edge_count(v) != 3) {
+        dissolve = false;
+      }
+    }
+    if (dissolve) {
+      BM_ITER_ELEM (v, &iter_b, f, BM_VERTS_OF_FACE) {
+        BM_elem_flag_set(v, BM_ELEM_TAG, true);
+      }
+    }
+  }
+  BM_mesh_delete_hflag_context(bm, BM_ELEM_TAG, DEL_VERTS);
+
+  BM_ITER_MESH (ed, &iter_a, bm, BM_EDGES_OF_MESH) {
+    if (BM_edge_face_count(ed) != 2) {
+      BM_elem_flag_set(ed, BM_ELEM_TAG, true);
+    }
+  }
+  BM_mesh_edgenet(bm, false, true);
+
+  /* Smooth the result */
+  for (int i = 0; i < 4; i++) {
+    BM_ITER_MESH (v, &iter_a, bm, BM_VERTS_OF_MESH) {
+      float co[3];
+      zero_v3(co);
+      BM_ITER_ELEM (ed, &iter_b, v, BM_EDGES_OF_VERT) {
+        BMVert *vert = BM_edge_other_vert(ed, v);
+        add_v3_v3(co, vert->co);
+      }
+      mul_v3_fl(co, 1.0f / (float)BM_vert_edge_count(v));
+      mid_v3_v3v3(v->co, v->co, co);
+    }
+  }
+
+  BM_mesh_elem_hflag_disable_all(bm, BM_VERT | BM_EDGE | BM_FACE, BM_ELEM_SELECT, false);
+
+  Mesh *result = BKE_mesh_from_bmesh_nomain(bm,
+                                            (&(struct BMeshToMeshParams){
+                                                .calc_object_remap = false,
+                                            }),
+                                            mesh);
+
+  BKE_id_free(NULL, mesh);
+  BM_mesh_free(bm);
+  return result;
+}