Sculpt: Fair Face Sets operation for Face Set Edit

This implements a mesh fairing algorithm and implements the fair
operations for Face Set edit. This edit operations create a smooth as
possible geometry patch in the area of the selected Face Set.

The mesh fairing algorithm is designed by Brett Fedack for the addon
"Mesh Fairing": https://github.com/fedackb/mesh-fairing, with some
modifications:

- The main fairing function in BKE_mesh_fair.h does not triangulate
 the mesh. For the test I did in sculpt mode results are good enough
 without triangulating the topology. Depending on the use and the
 result quality needed for a particular tool, the mesh can be
 triangulate in the affected area before starting fairing.

- Cotangents loop weights are not implemented yet. The idea is to
also expose the vertex and loop weights in a different function in
 case a tool needs to set up custom weights.

This algorithm will also be used to solve the limitations of line
project and implement the Lasso Project and Polyline Project tools.
It can also be used in tools in other areas of Blender, like Edit Mode
or future retopology tools.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D9603

1 files changed, 56 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_mesh_fair.h b/source/blender/blenkernel/BKE_mesh_fair.h
new file mode 100644
index 00000000000..2d5c85d4129
--- /dev/null
+++ b/source/blender/blenkernel/BKE_mesh_fair.h
@@ -0,0 +1,56 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * Mesh Fairing algorithm designed by Brett Fedack, used in the addon "Mesh Fairing":
+ * https://github.com/fedackb/mesh-fairing.
+ */
+
+#pragma once
+
+/** \file
+ * \ingroup bke
+ */
+
+#include "BLI_utildefines.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Mesh Fairing. */
+/* Creates a smooth as possible geometry patch in a defined area. Different values of depth allow
+ * to minimize changes in the vertex positions or tangency in the affected area. */
+
+typedef enum eMeshFairingDepth {
+  MESH_FAIRING_DEPTH_POSITION = 1,
+  MESH_FAIRING_DEPTH_TANGENCY = 2,
+} eMeshFairingDepth;
+
+/* affect_vertices is used to define the fairing area. Indexed by vertex index, set to true when
+ * the vertex should be modified by fairing. */
+void BKE_bmesh_prefair_and_fair_vertices(struct BMesh *bm,
+                                         bool *affect_vertices,
+                                         const eMeshFairingDepth depth);
+
+/* This function can optionally use the MVert coordinates of deform_mverts to read and write the
+ * fairing result. When NULL, the function will use mesh->mverts directly. */
+void BKE_mesh_prefair_and_fair_vertices(struct Mesh *mesh,
+                                        struct MVert *deform_mverts,
+                                        bool *affect_vertices,
+                                        const eMeshFairingDepth depth);
+
+#ifdef __cplusplus
+}
+#endif