[Bf-blender-cvs] [31d2283c3c1] soc-2021-adaptive-cloth: adaptive_cloth: AdaptiveMesh: no edge flip if inverted face normals

[ishbosamiya]

Commit: 31d2283c3c1fb1dad705bc8810082a6d7b2693bd
Author: ishbosamiya
Date:   Tue Aug 10 22:10:04 2021 +0530
Branches: soc-2021-adaptive-cloth
https://developer.blender.org/rB31d2283c3c1fb1dad705bc8810082a6d7b2693bd

adaptive_cloth: AdaptiveMesh: no edge flip if inverted face normals

Edge flippability test should prevent flipping of an edge that will
lead to inverted face normals.

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

M	source/blender/blenkernel/intern/cloth_remesh.cc

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

diff --git a/source/blender/blenkernel/intern/cloth_remesh.cc b/source/blender/blenkernel/intern/cloth_remesh.cc
index a4f04a2dcf5..7b633c41e2f 100644
--- a/source/blender/blenkernel/intern/cloth_remesh.cc
+++ b/source/blender/blenkernel/intern/cloth_remesh.cc
@@ -694,6 +694,27 @@ class AdaptiveMesh : public Mesh<NodeData<END>, VertData, EdgeData, internal::Em
       }
     }
 
+    /* Should not flip an edge that creates face(s) that are inverted */
+    {
+      const auto &f1 = this->get_checked_face(edge.get_faces()[0]);
+      const auto &f2 = this->get_checked_face(edge.get_faces()[1]);
+      const auto &ov1 = this->get_checked_other_vert(edge, f1);
+      const auto &ov2 = this->get_checked_other_vert(edge, f2);
+
+      const auto [v1, v2] = this->get_checked_verts_of_edge(edge, false);
+
+      const auto n1 = this->compute_face_normal(v1, ov2, ov1);
+      const auto n2 = this->compute_face_normal(v2, ov1, ov2);
+      const auto expected_normal = f1.get_normal() + f2.get_normal();
+
+      if (float3::dot(n1, expected_normal) <= 0.0) {
+        return false;
+      }
+      if (float3::dot(n2, expected_normal) <= 0.0) {
+        return false;
+      }
+    }
+
     const auto cross_2d = [](const float2 &a, const float2 &b) { return a.x * b.y - a.y * b.x; };
 
     /* Now the actual anisotropic aware critereon */