Geometry Nodes: add 'Intersecting Edges' output for boolean node

This patch adds a 'Intersecting Edges' output with a boolean selection
that only gives you the new edges on intersections.

Will work on a couple of examples next, this should make some
interesting effects possible (including getting us closer to the "bevel-
after-boolean-usecase")

To achieve this, a Vector is passed to `direct_mesh_boolean` when the
iMesh is still available (and intersecting edges appended), then from
those edge indices a selection will be stored as attribute.

Differential Revision: https://developer.blender.org/D15151

1 files changed, 19 insertions, 2 deletions

diff --git a/source/blender/blenkernel/intern/mesh_boolean_convert.cc b/source/blender/blenkernel/intern/mesh_boolean_convert.cc
index 14bd6aa5b2f..79bdc08fe8f 100644
--- a/source/blender/blenkernel/intern/mesh_boolean_convert.cc
+++ b/source/blender/blenkernel/intern/mesh_boolean_convert.cc
@@ -791,7 +791,8 @@ Mesh *direct_mesh_boolean(Span<const Mesh *> meshes,
                           Span<Array<short>> material_remaps,
                           const bool use_self,
                           const bool hole_tolerant,
-                          const int boolean_mode)
+                          const int boolean_mode,
+                          Vector<int> *r_intersecting_edges)
 {
 #ifdef WITH_GMP
   BLI_assert(meshes.size() == transforms.size());
@@ -828,7 +829,23 @@ Mesh *direct_mesh_boolean(Span<const Mesh *> meshes,
     write_obj_mesh(m_out, "m_out");
   }
 
-  return imesh_to_mesh(&m_out, mim);
+  Mesh *result = imesh_to_mesh(&m_out, mim);
+
+  /* Store intersecting edge indices. */
+  if (r_intersecting_edges != nullptr) {
+    for (int fi : m_out.face_index_range()) {
+      const Face &face = *m_out.face(fi);
+      const MPoly &poly = result->mpoly[fi];
+      for (int corner_i : face.index_range()) {
+        if (face.is_intersect[corner_i]) {
+          int e_index = result->mloop[poly.loopstart + corner_i].e;
+          r_intersecting_edges->append(e_index);
+        }
+      }
+    }
+  }
+
+  return result;
 #else   // WITH_GMP
   UNUSED_VARS(meshes,
               transforms,