[Bf-blender-cvs] [79cad4c0b6a] soc-2021-adaptive-cloth: adaptive_cloth: Mesh: flip_edge_triangulate() initial implementation

[ishbosamiya]

Commit: 79cad4c0b6a6581b0884b8e9ddc930b0ac862016
Author: ishbosamiya
Date:   Wed Jul 14 10:46:35 2021 +0530
Branches: soc-2021-adaptive-cloth
https://developer.blender.org/rB79cad4c0b6a6581b0884b8e9ddc930b0ac862016

adaptive_cloth: Mesh: flip_edge_triangulate() initial implementation

Need to implement across seams support.

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

M	source/blender/blenkernel/BKE_cloth_remesh.hh
M	source/blender/makesdna/DNA_modifier_types.h
M	source/blender/makesrna/intern/rna_modifier.c
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 0ca39240fc0..b70ff8967f3 100644
--- a/source/blender/blenkernel/BKE_cloth_remesh.hh
+++ b/source/blender/blenkernel/BKE_cloth_remesh.hh
@@ -1646,6 +1646,85 @@ template<typename END, typename EVD, typename EED, typename EFD> class Mesh {
                     std::move(deleted_faces));
   }
 
+  /**
+   * An edge is flippable only if the edge has exactly 2 faces, and
+   * both faces are triangulated.
+   */
+  bool is_edge_flippable(EdgeIndex edge_index, bool across_seams) const
+  {
+    /* TODO(ish): handle across_seams */
+    const auto &edge = this->get_checked_edge(edge_index);
+    if (edge.faces.size() != 2) {
+      return false;
+    }
+
+    for (const auto &face_index : edge.faces) {
+      const auto &face = this->get_checked_face(face_index);
+      if (face.verts.size() != 3) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+  /**
+   * Flips the edge specified and ensures triangulation of the Mesh.
+   *
+   * @param across_seams If true, think of edge as world space edge
+   * and not UV space, this means, all the faces across all the edges
+   * formed between the nodes of the given edge are used for flipping
+   * regardless if it on a seam or not.
+   *
+   * Returns the `MeshDiff` that lead to the operation.
+   *
+   * Note, the caller must ensure the adjacent faces to the edge are
+   * triangulated and that they are flippable using
+   * `is_edge_flippable()`. In debug mode, it will assert, in release
+   * mode, it is undefined behaviour.
+   **/
+  MeshDiff<END, EVD, EED, EFD> flip_edge_triangulate(EdgeIndex edge_index, bool across_seams)
+  {
+    BLI_assert(this->is_edge_flippable(edge_index, across_seams));
+
+    /* This operation deletes the following:
+     * None
+     *
+     * This operation adds the following:
+     * None
+     */
+
+    /* Let `e` be the edge of `edge_index`
+     * Let `v1` be the first vert of `e`
+     * Let `v2` be the second vert of `e`
+     * Let `f1` be the first face of `e`
+     * Let `f2` be the second face of `e`
+     * Let `ov1` be the other vert of `f1`
+     * Let `ov2` be the other vert of `f2`
+     */
+
+    auto &e = this->get_checked_edge(edge_index);
+    auto [v1, v2] = this->get_checked_verts_of_edge(e, false);
+    auto v1_index = v1.self_index;
+    auto v2_index = v2.self_index;
+    auto &f1 = this->get_checked_face(e.faces[0]);
+    auto &f2 = this->get_checked_face(e.faces[1]);
+    auto &ov1 = this->get_checked_other_vert(e, f1);
+    auto &ov2 = this->get_checked_other_vert(e, f2);
+    auto ov1_index = ov1.self_index;
+    auto ov2_index = ov2.self_index;
+    e.verts = {ov1_index, ov2_index};
+    f1.verts = {v1_index, ov2_index, ov1_index};
+    f2.verts = {v2_index, ov1_index, ov2_index};
+
+    v1.edges.remove_first_occurrence_and_reorder(edge_index);
+    v2.edges.remove_first_occurrence_and_reorder(edge_index);
+    ov1.edges.append(edge_index);
+    ov2.edges.append(edge_index);
+
+    return MeshDiff<END, EVD, EED, EFD>();
+  }
+
  protected:
   /* all protected static methods */
   /* all protected non-static methods */
diff --git a/source/blender/makesdna/DNA_modifier_types.h b/source/blender/makesdna/DNA_modifier_types.h
index 8b9cd15be40..cc1e903e763 100644
--- a/source/blender/makesdna/DNA_modifier_types.h
+++ b/source/blender/makesdna/DNA_modifier_types.h
@@ -2367,6 +2367,7 @@ typedef enum AdaptiveRemeshFlag {
 typedef enum AdaptiveRemeshMode {
   ADAPTIVE_REMESH_SPLIT_EDGE = 0,
   ADAPTIVE_REMESH_COLLAPSE_EDGE = 1,
+  ADAPTIVE_REMESH_FLIP_EDGE = 2,
 } AdaptiveRemeshMode;
 
 #ifdef __cplusplus
diff --git a/source/blender/makesrna/intern/rna_modifier.c b/source/blender/makesrna/intern/rna_modifier.c
index 0e43feb72f7..ac2414220dd 100644
--- a/source/blender/makesrna/intern/rna_modifier.c
+++ b/source/blender/makesrna/intern/rna_modifier.c
@@ -7239,6 +7239,7 @@ static void rna_def_modifier_adaptive_remesh(BlenderRNA *brna)
        0,
        "Collapse Edge",
        "Collapse edge of given index"},
+      {ADAPTIVE_REMESH_FLIP_EDGE, "FLIP_EDGE", 0, "Flip Edge", "Flip edge of given index"},
       {0, NULL, 0, NULL, NULL},
   };
 
diff --git a/source/blender/modifiers/intern/MOD_adaptive_remesh.cc b/source/blender/modifiers/intern/MOD_adaptive_remesh.cc
index 64973878eaa..72472a584c0 100644
--- a/source/blender/modifiers/intern/MOD_adaptive_remesh.cc
+++ b/source/blender/modifiers/intern/MOD_adaptive_remesh.cc
@@ -69,6 +69,13 @@ static Mesh *modifyMesh(ModifierData *md, const ModifierEvalContext *UNUSED(ctx)
     else if (mode == ADAPTIVE_REMESH_COLLAPSE_EDGE) {
       internal_mesh.collapse_edge_triangulate(edge_index, verts_swapped, across_seams);
     }
+    else if (mode == ADAPTIVE_REMESH_FLIP_EDGE) {
+      auto flippable = internal_mesh.is_edge_flippable(edge_index, across_seams);
+      std::cout << "flippable: " << flippable << std::endl;
+      if (flippable) {
+        internal_mesh.flip_edge_triangulate(edge_index, across_seams);
+      }
+    }
   }
 
   internal::MeshIO writer = internal_mesh.write();