Add basic viewer for polygon.

Polygon/doc/Polygon/Polygon.txt

@@ -70,6 +70,18 @@ and 3D Linear Geometric %Kernel.
 
 \cgalExample{Polygon/projected_polygon.cpp}
 
+\subsection subsecPolygonDraw Draw a Polygon
+
+A polygon can be visualized by calling the `CGAL::draw()` function as shown in the following example. This function opens a new window showing the given polygon. The function is blocking, that is the program continues as soon as the user closes the window.
+
+\cgalExample{Polygon/draw_polygon.cpp}
+
+This function requires CGAL_Qt5, and is only available if the flag CGAL_USE_BASIC_VIEWER is defined at compile time.
+
+\cgalFigureBegin{fig_draw_polygon,draw_polygon.png}
+Result of the run of the draw_polygon program. A window shows the polygon and allows to navigate through the scene.
+\cgalFigureEnd
+
 */
 
 \section secPolygonWithHole Polygons with Holes

Polygon/doc/Polygon/examples.txt

@@ -3,4 +3,5 @@
 \example Polygon/polygon_algorithms.cpp
 \example Polygon/Polygon.cpp
 \example Polygon/projected_polygon.cpp
+\example Polygon/draw_polygon.cpp
 */

Polygon/examples/Polygon/CMakeLists.txt

@@ -6,7 +6,11 @@ project( Polygon_Examples )
 
 cmake_minimum_required(VERSION 2.8.10)
 
-find_package(CGAL QUIET)
+find_package(CGAL QUIET COMPONENTS Qt5)
+
+if(CGAL_Qt5_FOUND)
+    add_definitions(-DCGAL_USE_BASIC_VIEWER -DQT_NO_KEYWORDS)
+endif()
 
 if ( CGAL_FOUND )
 
@@ -22,6 +26,10 @@ if ( CGAL_FOUND )
     create_single_source_cgal_program( "${cppfile}" )
   endforeach()
 
+  if(CGAL_Qt5_FOUND)
+    target_link_libraries(draw_polygon PUBLIC CGAL::CGAL_Qt5)
+  endif()
+
 else()
   
     message(STATUS "This program requires the CGAL library, and will not be compiled.")

Polygon/examples/Polygon/draw_polygon.cpp

@@ -0,0 +1,22 @@
+#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
+#include <CGAL/Polygon_2.h>
+#include <CGAL/draw_polygon_2.h>
+
+typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
+typedef CGAL::Polygon_2<K>                                  Polygon_2;
+typedef CGAL::Point_2<K>                                    Point;
+
+int main()
+{
+  // create a polygon and put some points in it
+  Polygon_2 p;
+  p.push_back(Point(0,0));
+  p.push_back(Point(4,0));
+  p.push_back(Point(4,4));
+  p.push_back(Point(2,2));
+  p.push_back(Point(0,4));
+
+  CGAL::draw(p);
+
+  return EXIT_SUCCESS;
+}

Polygon/include/CGAL/draw_polygon_2.h

@@ -0,0 +1,131 @@
+// Copyright (c) 1997  
+// Utrecht University (The Netherlands),
+// ETH Zurich (Switzerland),
+// INRIA Sophia-Antipolis (France),
+// Max-Planck-Institute Saarbruecken (Germany),
+// and Tel-Aviv University (Israel).  All rights reserved. 
+//
+// This file is part of CGAL (www.cgal.org); you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation; either version 3 of the License,
+// or (at your option) any later version.
+//
+// Licensees holding a valid commercial license may use this file in
+// accordance with the commercial license agreement provided with the software.
+//
+// This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
+// WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+//
+// $URL$
+// $Id$
+// SPDX-License-Identifier: LGPL-3.0+
+// 
+//
+// Author(s)     : Guillaume Damiand <guillaume.damiand@liris.cnrs.fr>
+
+#ifndef CGAL_DRAW_POLYGON_2_H
+#define CGAL_DRAW_POLYGON_2_H
+
+#include <CGAL/Qt/Basic_viewer_qt.h>
+
+#ifdef CGAL_USE_BASIC_VIEWER
+
+#include <CGAL/Polygon_2.h>
+#include <CGAL/Random.h>
+
+namespace CGAL
+{
+  
+// Viewer class for Polygon_2 
+template<class P2>
+class SimplePolygon2ViewerQt : public Basic_viewer_qt
+{
+  typedef Basic_viewer_qt      Base;
+  typedef typename P2::Point_2 Point;
+ 
+public:
+  /// Construct the viewer.
+  /// @param ap2 the polygon to view
+  /// @param title the title of the window
+  SimplePolygon2ViewerQt(QWidget* parent, const P2& ap2,
+                         const char* title="Basic Polygon_2 Viewer") :
+    // First draw: vertices; edges, faces; multi-color; no inverse normal
+    Base(parent, title, true, true, true, false, false), 
+    p2(ap2)
+  {
+    compute_elements();
+  }
+
+protected:
+  void compute_elements()
+  {
+    clear();
+
+    if (p2.is_empty()) return;
+    
+    Point prev=p2.vertex(p2.size()-1);
+      
+    CGAL::Color c(75,160,255);
+    face_begin(c);
+
+    for (typename P2::Vertex_const_iterator i=p2.vertices_begin();
+         i!=p2.vertices_end(); ++i)
+    {
+      add_point(*i);         // Add vertex
+      add_segment(prev, *i); // Add segment with previous point
+      add_point_in_face(*i); // Add point in face
+      prev=*i;
+    }
+
+    face_end();
+  }
+
+  virtual void keyPressEvent(QKeyEvent *e)
+  {
+    // Test key pressed:
+    //    const ::Qt::KeyboardModifiers modifiers = e->modifiers();
+    //    if ((e->key()==Qt::Key_PageUp) && (modifiers==Qt::NoButton)) { ... }
+    
+    // Call: * compute_elements() if the model changed, followed by
+    //       * redraw() if some viewing parameters changed that implies some
+    //                  modifications of the buffers
+    //                  (eg. type of normal, color/mono)
+    //       * update() just to update the drawing
+
+    // Call the base method to process others/classicals key
+    Base::keyPressEvent(e);
+  }
+
+protected:
+  const P2& p2;
+};
+
+// Specialization of draw function.
+template<class T, class C>
+void draw(const CGAL::Polygon_2<T, C>& ap2,
+          const char* title="Polygon_2 Basic Viewer",
+          bool nofill=false)
+{
+#if defined(CGAL_TEST_SUITE)
+  bool cgal_test_suite=true;
+#else
+  bool cgal_test_suite=qEnvironmentVariableIsSet("CGAL_TEST_SUITE");
+#endif
+  
+  if (!cgal_test_suite)
+  {
+    int argc=1;
+    const char* argv[2]={"t2_viewer","\0"};
+    QApplication app(argc,const_cast<char**>(argv));
+    SimplePolygon2ViewerQt<CGAL::Polygon_2<T, C> >
+      mainwindow(app.activeWindow(), ap2, title);
+    mainwindow.show();
+    app.exec();
+  }
+}
+
+} // End namespace CGAL
+
+#endif // CGAL_USE_BASIC_VIEWER
+
+#endif // CGAL_DRAW_POLYGON_2_H