From 730bbba98bbce3c9983644e02a66fb45c508cdf2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Loriot?= <sebastien.loriot@cgal.org>
Date: Mon, 20 Nov 2023 10:03:16 +0100
Subject: [PATCH] add an example with a dummy custom sizing field

---
 .../Polygon_mesh_processing/CMakeLists.txt    |   1 +
 ...c_remeshing_with_custom_sizing_example.cpp | 102 ++++++++++++++++++
 2 files changed, 103 insertions(+)
 create mode 100644 Polygon_mesh_processing/examples/Polygon_mesh_processing/isotropic_remeshing_with_custom_sizing_example.cpp

diff --git a/Polygon_mesh_processing/examples/Polygon_mesh_processing/CMakeLists.txt b/Polygon_mesh_processing/examples/Polygon_mesh_processing/CMakeLists.txt
index 590305c0c8a..38d1bce078b 100644
--- a/Polygon_mesh_processing/examples/Polygon_mesh_processing/CMakeLists.txt
+++ b/Polygon_mesh_processing/examples/Polygon_mesh_processing/CMakeLists.txt
@@ -51,6 +51,7 @@ create_single_source_cgal_program("match_faces.cpp")
 create_single_source_cgal_program("cc_compatible_orientations.cpp")
 create_single_source_cgal_program("hausdorff_distance_remeshing_example.cpp")
 create_single_source_cgal_program("hausdorff_bounded_error_distance_example.cpp")
+create_single_source_cgal_program("isotropic_remeshing_with_custom_sizing_example.cpp")
 
 find_package(Eigen3 3.2.0 QUIET) #(requires 3.2.0 or greater)
 include(CGAL_Eigen3_support)
diff --git a/Polygon_mesh_processing/examples/Polygon_mesh_processing/isotropic_remeshing_with_custom_sizing_example.cpp b/Polygon_mesh_processing/examples/Polygon_mesh_processing/isotropic_remeshing_with_custom_sizing_example.cpp
new file mode 100644
index 00000000000..1fc70906f7d
--- /dev/null
+++ b/Polygon_mesh_processing/examples/Polygon_mesh_processing/isotropic_remeshing_with_custom_sizing_example.cpp
@@ -0,0 +1,102 @@
+#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
+#include <CGAL/Surface_mesh.h>
+#include <CGAL/Polygon_mesh_processing/remesh.h>
+#include <CGAL/Polygon_mesh_processing/IO/polygon_mesh_io.h>
+#include <CGAL/Polygon_mesh_processing/bbox.h>
+
+#include <fstream>
+
+typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
+typedef CGAL::Surface_mesh<K::Point_3> Mesh;
+
+namespace PMP = CGAL::Polygon_mesh_processing;
+
+// a sizing fied that is increasing the size of edge along the y-axis
+// starting at a minimum size at y-max and ending at a maximum size at
+// y-min, with a linear interpolation of sizes in between the two extreme
+// sizing values
+struct My_sizing_field
+{
+  double min_size, max_size;
+  double ymin, ymax;
+  const Mesh& mesh;
+
+  My_sizing_field(double min_size, double max_size, double ymin, double ymax, const Mesh& mesh)
+    : min_size(min_size)
+    , max_size(max_size)
+    , ymin(ymin)
+    , ymax(ymax)
+    , mesh(mesh)
+  {}
+
+  double at(K::Point_3 p) const
+  {
+    double y=p.y();
+    return CGAL::square( (y-ymin)/(ymax-ymin) * (min_size - max_size) + max_size );
+  }
+  double at(const Mesh::Vertex_index v) const { return at(mesh.point(v)); }
+
+  std::optional<double> is_too_long(const Mesh::Vertex_index va,
+                                    const Mesh::Vertex_index vb) const
+  {
+    // TODO: no mesh as parameters?
+    K::Point_3 mp = CGAL::midpoint(mesh.point(va), mesh.point(vb));
+    double sql_at = at(mp);
+    double sql = CGAL::squared_distance(mesh.point(va), mesh.point(vb));
+    if (sql > sql_at)
+      return sql / sql_at;
+    return std::nullopt;
+  }
+
+  std::optional<double> is_too_short(const Mesh::Halfedge_index h,
+                                     const Mesh&) const
+  {
+    K::Point_3 mp = CGAL::midpoint(mesh.point(source(h, mesh)), mesh.point(target(h, mesh)));
+    double sql_at = at(mp);
+    double sql = CGAL::squared_distance(mesh.point(source(h, mesh)), mesh.point(target(h, mesh)));
+    if (sql < sql_at)
+      return sql / sql_at;
+    return std::nullopt;
+  }
+
+  K::Point_3 split_placement(const Mesh::Halfedge_index h,
+                          const Mesh&) const
+  {
+    return CGAL::midpoint(mesh.point(source(h, mesh)), mesh.point(target(h, mesh)));
+  }
+
+  void update(const Mesh::Vertex_index, const Mesh&) {}
+};
+
+
+int main(int argc, char* argv[])
+{
+  const std::string filename = (argc > 1) ? argv[1] : CGAL::data_file_path("meshes/elk.off");
+
+  Mesh mesh;
+  if (!PMP::IO::read_polygon_mesh(filename, mesh) || !CGAL::is_triangle_mesh(mesh)) {
+    std::cerr << "Not a valid input file." << std::endl;
+    return 1;
+  }
+
+  std::cout << "Start remeshing of " << filename
+    << " (" << num_faces(mesh) << " faces)..." << std::endl;
+
+  CGAL::Bbox_3 bb = PMP::bbox(mesh);
+  My_sizing_field sizing_field(0.1, 30, bb.ymin(), bb.ymax(), mesh);
+  unsigned int nb_iter = 5;
+
+  PMP::isotropic_remeshing(
+      faces(mesh),
+      sizing_field,
+      mesh,
+      CGAL::parameters::number_of_iterations(nb_iter)
+                       .number_of_relaxation_steps(3)
+      );
+
+  CGAL::IO::write_polygon_mesh("custom_remesh_out.off", mesh, CGAL::parameters::stream_precision(17));
+
+  std::cout << "Remeshing done." << std::endl;
+
+  return 0;
+}