add CGAL::draw for CCDT_3

Constrained_triangulation_3/doc/Constrained_triangulation_3/PackageDescription.txt

@@ -10,6 +10,9 @@
 \defgroup PkgConstrainedTriangulation3Classes Classes and Class Templates
 \ingroup PkgConstrainedTriangulation3Ref
 
+\defgroup PkgDrawCDT_3 Draw a 3D Constrained Triangulation
+\ingroup PkgConstrainedTriangulation3Ref
+
 \addtogroup PkgConstrainedTriangulation3Ref
 \cgalPkgDescriptionBegin{3D Constrained Triangulations,PkgConstrainedTriangulation3}
 \cgalPkgPicture{cdt3-small.png}
@@ -56,4 +59,9 @@ a conforming constrained Delaunay triangulation in 3D, an instance of the class
 - `CGAL::Conforming_constrained_Delaunay_triangulation_3<Traits, Triangulation>`
 - `CGAL::Conforming_constrained_Delaunay_triangulation_vertex_base_3<Traits, Vertex_base>`
 - `CGAL::Conforming_constrained_Delaunay_triangulation_cell_base_3<Traits, Cell_base>`
+
+\cgalCRPSection{Draw a 3D Constrained Triangulation}
+
+- \link PkgDrawCDT_3 CGAL::draw() \endlink
+
 */

Constrained_triangulation_3/examples/Constrained_triangulation_3/conforming_constrained_Delaunay_triangulation_3.cpp

@@ -1,7 +1,7 @@
 #include <CGAL/make_conforming_constrained_Delaunay_triangulation_3.h>
 #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
 #include <CGAL/Surface_mesh.h>
-#include <CGAL/draw_triangulation_3.h>
+#include <CGAL/draw_constrained_triangulation_3.h>
 
 #include <algorithm>
 
@@ -28,7 +28,7 @@ int main(int argc, char* argv[])
             << "Number of constrained facets in the CDT: "
             << ccdt.number_of_constrained_facets() << '\n';
 
-  CGAL::draw(ccdt.triangulation());
+  CGAL::draw(ccdt);
 
   return EXIT_SUCCESS;
-}
+}

Constrained_triangulation_3/examples/Constrained_triangulation_3/conforming_constrained_Delaunay_triangulation_3_from_soup.cpp

@@ -1,7 +1,7 @@
 #include <CGAL/make_conforming_constrained_Delaunay_triangulation_3.h>
 #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
 #include <vector>
-#include <CGAL/draw_triangulation_3.h>
+#include <CGAL/draw_constrained_triangulation_3.h>
 
 #include <algorithm>
 
@@ -29,7 +29,7 @@ int main(int argc, char* argv[])
             << "Number of constrained facets in the CDT: "
             << ccdt.number_of_constrained_facets() << '\n';
 
-  CGAL::draw(ccdt.triangulation());
+  CGAL::draw(ccdt);
 
   return EXIT_SUCCESS;
 }

Constrained_triangulation_3/examples/Constrained_triangulation_3/conforming_constrained_Delaunay_triangulation_3_from_soup_fpmap.cpp

@@ -1,5 +1,5 @@
 // Copy the content from the old file to the new file, but update all occurrences of 'fmap' in the filename and code to 'fpmap'.
-#include <CGAL/draw_triangulation_3.h>
+#include <CGAL/draw_constrained_triangulation_3.h>
 #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
 #include <CGAL/make_conforming_constrained_Delaunay_triangulation_3.h>
 #include <CGAL/Polygon_mesh_processing/connected_components.h>
@@ -57,7 +57,8 @@ int main(int argc, char* argv[])
             << "Number of constrained facets in the CDT: "
             << ccdt.number_of_constrained_facets() << '\n';
 
-  CGAL::draw(ccdt.triangulation());
+
+  CGAL::draw(ccdt);
 
   return EXIT_SUCCESS;
 }

Constrained_triangulation_3/include/CGAL/Conforming_constrained_Delaunay_triangulation_3.h

@@ -14,6 +14,8 @@
 
 #include <CGAL/license/Constrained_triangulation_3.h>
 
+#include <CGAL/Conforming_constrained_Delaunay_triangulation_3_fwd.h>
+
 #include <CGAL/Constrained_triangulation_3/internal/config.h>
 
 #include <CGAL/Base_with_time_stamp.h>
@@ -876,7 +878,7 @@ public:
     * This allows the use of all non-modifying functions of the base triangulation.
     * See the other overload for a way to move the triangulation out of this object and then modify it.
     */
-  const Triangulation& triangulation() & {
+  const Triangulation& triangulation() const& {
     return cdt_impl;
   }
 

Constrained_triangulation_3/include/CGAL/Conforming_constrained_Delaunay_triangulation_3_fwd.h

@@ -0,0 +1,24 @@
+// Copyright (c) 2025  GeometryFactory Sarl (France).
+// All rights reserved.
+//
+// This file is part of CGAL (www.cgal.org).
+//
+// $URL$
+// $Id$
+// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
+//
+// Author(s)     : Laurent Rineau
+
+#ifndef CGAL_CONFORMING_CONSTRAINED_DELAUNAY_TRIANGULATION_3_FWD_H
+#define CGAL_CONFORMING_CONSTRAINED_DELAUNAY_TRIANGULATION_3_FWD_H
+
+#include <CGAL/license/Constrained_triangulation_3.h>
+
+namespace CGAL {
+
+template <typename Traits, typename Tr>
+class Conforming_constrained_Delaunay_triangulation_3;
+
+} // namespace CGAL
+
+#endif // CGAL_CONFORMING_CONSTRAINED_DELAUNAY_TRIANGULATION_3_FWD_H

Constrained_triangulation_3/include/CGAL/draw_constrained_triangulation_3.h

@@ -0,0 +1,88 @@
+// Copyright (c) 2025 GeometryFactory SARL (France).
+// All rights reserved.
+//
+// This file is part of CGAL (www.cgal.org).
+//
+// $URL$
+// $Id$
+// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
+//
+// Author(s)     : Laurent Rineau
+
+#ifndef CGAL_DRAW_CONSTRAINED_T3_H
+#define CGAL_DRAW_CONSTRAINED_T3_H
+
+#include <CGAL/license/Constrained_triangulation_3.h>
+#include <CGAL/draw_triangulation_3.h>
+#include <CGAL/Conforming_constrained_Delaunay_triangulation_3_fwd.h>
+#include <CGAL/type_traits.h>
+#include <algorithm>
+
+namespace CGAL {
+#if defined(CGAL_USE_BASIC_VIEWER) || defined(DOXYGEN_RUNNING)
+
+/*!
+\ingroup PkgDrawCDT_3
+
+opens a new window and draws the constrained triangulation.
+
+A call to this function blocks the execution of the program until the drawing window is closed. This function requires `CGAL_Qt6`, and is only available if the macro `CGAL_USE_BASIC_VIEWER` is defined.
+Linking with the cmake target `CGAL::CGAL_Basic_viewer` will link with `CGAL_Qt6` and add the definition `CGAL_USE_BASIC_VIEWER`.
+*/
+template <typename Traits, typename Tr_or_default>
+void draw(const Conforming_constrained_Delaunay_triangulation_3<Traits, Tr_or_default>& ccdt,
+          const char *title="Constrained 3D Triangulation Basic Viewer")
+{
+  using Tr = CGAL::cpp20::remove_cvref_t<decltype(ccdt.triangulation())>;
+  using Vertex_handle = typename Tr::Vertex_handle;
+  using Cell_handle = typename Tr::Cell_handle;
+  using Edge_descriptor = typename Tr::Finite_edges_iterator;
+  using Facet_descriptor = typename Tr::Finite_facets_iterator;
+
+  using Face_index = CGAL::cpp20::remove_cvref_t<
+      decltype(std::declval<Cell_handle>()->surface_patch_index(0))>;
+
+  Face_index nb_colors = 0;
+  std::for_each(
+      ccdt.constrained_facets_begin(), ccdt.constrained_facets_end(),
+      [&](const auto& f) {
+        auto [c, index] = f;
+        nb_colors = (std::max)(nb_colors, c->ccdt_3_data().face_constraint_index(index) + 1);
+      });
+  std::vector<CGAL::IO::Color> colors(nb_colors);
+  std::generate(colors.begin(), colors.end(), []() {
+    return CGAL::get_random_color(CGAL::get_default_random());
+  });
+  CGAL::Graphics_scene_options<Tr, Vertex_handle, Edge_descriptor, Facet_descriptor> options;
+  options.draw_face = [](const Tr&, Facet_descriptor f) {
+    auto [c, index] = *f;
+    return c->ccdt_3_data().is_facet_constrained(index);
+  };
+  options.colored_face = [](const Tr&, Facet_descriptor f) {
+    return true;
+  };
+  options.face_color = [&](const Tr&, Facet_descriptor f) {
+    auto [c, index] = *f;
+    return colors[c->ccdt_3_data().face_constraint_index(index)];
+  };
+  draw(ccdt.triangulation(), options, title);
+}
+
+/*!
+\ingroup PkgDrawCDT_3
+
+A shortcut to \link PkgDrawTriangulation3 `CGAL::add_to_graphics_scene(ccdt.triangulation(), gs_options, title)` \endlink.
+*/
+template <typename Traits, typename Tr, typename GSOptions>
+void draw(const Conforming_constrained_Delaunay_triangulation_3<Traits, Tr>& ccdt,
+          const GSOptions& gs_options,
+          const char *title="Constrained 3D Triangulation Basic Viewer")
+{
+  draw(ccdt.triangulation(), gs_options, title);
+}
+
+#endif // CGAL_USE_BASIC_VIEWER || DOXYGEN_RUNNING
+
+} // End namespace CGAL
+
+#endif // CGAL_DRAW_CONSTRAINED_T3_H