[Bf-blender-cvs] [cae9f4dd954] soc-2021-adaptive-cloth: adaptive_cloth: mesh: is_edge_collapseable()

[ishbosamiya]

Commit: cae9f4dd9549cc188c59db9dbac4d531ec0b6f00
Author: ishbosamiya
Date:   Wed Aug 4 11:27:33 2021 +0530
Branches: soc-2021-adaptive-cloth
https://developer.blender.org/rBcae9f4dd9549cc188c59db9dbac4d531ec0b6f00

adaptive_cloth: mesh: is_edge_collapseable()

The collapse edge operation doesn't support one type of edge
collapse. When the collapse is across seams, it is possible for one
vert v1 to be asked to collapsed into multiple verts v2. Now deciding
which v2 to consider is a difficult task, so not handling it right now.

===================================================================

M	source/blender/blenkernel/BKE_cloth_remesh.hh
M	source/blender/modifiers/intern/MOD_adaptive_remesh.cc

===================================================================

diff --git a/source/blender/blenkernel/BKE_cloth_remesh.hh b/source/blender/blenkernel/BKE_cloth_remesh.hh
index e34db56d413..5a2c3ff1fef 100644
--- a/source/blender/blenkernel/BKE_cloth_remesh.hh
+++ b/source/blender/blenkernel/BKE_cloth_remesh.hh
@@ -1796,6 +1796,52 @@ template<typename END, typename EVD, typename EED, typename EFD> class Mesh {
                     std::move(deleted_faces));
   }
 
+  bool is_edge_collapseable(EdgeIndex edge_index, bool verts_swapped, bool across_seams)
+  {
+    /* The edge is always collapseable if across seams is false */
+    if (across_seams == false) {
+      return true;
+    }
+
+    auto &e_a = this->get_checked_edge(edge_index);
+    auto [v1_a, v2_a] = this->get_checked_verts_of_edge(e_a, verts_swapped);
+    auto &n1_a = this->get_checked_node_of_vert(v1_a);
+    auto &n2_a = this->get_checked_node_of_vert(v2_a);
+    auto n1_index = n1_a.self_index;
+    auto edge_indices = this->get_connecting_edge_indices(n1_a, n2_a);
+
+    /* The collapse edge function doesn't support collapsing one v1 into
+     * multiple v2 as of right now, so if we find such a case tell
+     * user that edge is not collapseable */
+    {
+      auto get_v1_v2_indices = [this, &n1_index, &verts_swapped](const Edge<EED> &e) {
+        auto [v1, v2] = this->get_checked_verts_of_edge(e, verts_swapped);
+        auto v1_index = v1.self_index;
+        auto v2_index = v2.self_index;
+        /* Need to swap the verts if v1 does not point to n1 */
+        if (v1.node.value() != n1_index) {
+          std::swap(v1_index, v2_index);
+        }
+        BLI_assert(this->get_checked_vert(v1_index).node.value() == n1_index);
+        return std::make_tuple(v1_index, v2_index);
+      };
+
+      blender::Vector<VertIndex> v1_list;
+      for (const auto &edge_index : edge_indices) {
+        auto &e = this->get_checked_edge(edge_index);
+        auto [v1_index, v2_index] = get_v1_v2_indices(e);
+
+        if (v1_list.contains(v1_index)) {
+          return false;
+        }
+
+        v1_list.append(v1_index);
+      }
+    }
+
+    return true;
+  }
+
   /**
    * Collapses the edge from edge v1 to v2 unless `verts_swapped` is set
    * to true and keeps the triangulation of the Mesh
@@ -1813,6 +1859,8 @@ template<typename END, typename EVD, typename EED, typename EFD> class Mesh {
    * Note, the caller must ensure the adjacent faces to the edge are
    * triangulated. In debug mode, it will assert, in release mode, it
    * is undefined behaviour.
+   *
+   * Caller must ensure that the edge is collapseable by calling `is_edge_collapseable()`
    **/
   MeshDiff<END, EVD, EED, EFD> collapse_edge_triangulate(EdgeIndex edge_index,
                                                          bool verts_swapped,
@@ -1843,6 +1891,8 @@ template<typename END, typename EVD, typename EED, typename EFD> class Mesh {
     FilenameGen filename_gen(
         "/tmp/adaptive_cloth/" + std::to_string(std::get<0>(edge_index.get_raw())), ".mesh");
 
+    BLI_assert(this->is_edge_collapseable(edge_index, verts_swapped, across_seams));
+
     blender::Vector<NodeIndex> added_nodes;
     blender::Vector<VertIndex> added_verts;
     blender::Vector<EdgeIndex> added_edges;
diff --git a/source/blender/modifiers/intern/MOD_adaptive_remesh.cc b/source/blender/modifiers/intern/MOD_adaptive_remesh.cc
index 09d5b8c27db..707dd43f09a 100644
--- a/source/blender/modifiers/intern/MOD_adaptive_remesh.cc
+++ b/source/blender/modifiers/intern/MOD_adaptive_remesh.cc
@@ -96,6 +96,9 @@ static Mesh *modifyMesh(ModifierData *md, const ModifierEvalContext *UNUSED(ctx)
     std::cout << "is_on_boundary: " << is_on_boundary << std::endl;
     auto flippable = internal_mesh.is_edge_flippable(edge_index, across_seams);
     std::cout << "flippable: " << flippable << std::endl;
+    auto collapseable = internal_mesh.is_edge_collapseable(
+        edge_index, verts_swapped, across_seams);
+    std::cout << "collapseable: " << collapseable << std::endl;
     if (mode == ADAPTIVE_REMESH_SPLIT_EDGE) {
       auto pre_split_msgpack = internal_mesh.serialize();
       auto pre_split_filename = split_edge_name_gen.get_curr(filename_pre_suffix + "_pre");