Provided by: libopengl-perl_0.7000+dfsg-3_amd64 bug

NAME

       OpenGL::Tessellation - discussion of tessellation in POGL

SYNOPSIS

           # somewhere in your drawing routine or drawlist compilation

           my $tess = gluNewTess();

           gluTessCallback($tess, GLU_TESS_BEGIN,     'DEFAULT');
           gluTessCallback($tess, GLU_TESS_END,       'DEFAULT');
           gluTessCallback($tess, GLU_TESS_VERTEX,    'DEFAULT');
           gluTessCallback($tess, GLU_TESS_COMBINE,   'DEFAULT');
           gluTessCallback($tess, GLU_TESS_ERROR,     'DEFAULT');
           gluTessCallback($tess, GLU_TESS_EDGE_FLAG, 'DEFAULT');

           gluTessBeginPolygon($tess);
           gluTessBeginContour($tess);

           gluTessVertex_p($tess, 0,     200, 0);
           gluTessVertex_p($tess, 150,  -200, 0);
           gluTessVertex_p($tess, 0,    -100, 0);
           gluTessVertex_p($tess, -150, -200, 0);

           gluTessEndContour($tess);
           gluTessEndPolygon($tess);

           gluDeleteTess($tess);

DESCRIPTION

       OpenGL rendering hardware typically does not have support for drawing concave polygons or
       drawing polygons with windows.  OpenGL provides glu extensions that allow for translating
       concave polygon vertices into triangles that can be rendered quickly on GL hardware.  The
       OpenGL red book chapter 11 has the full discussion of Tessellators and the OpenGL
       functions (http://glprogramming.com/red/chapter11.html, or use your favorite search engine
       and search for "opengl gluNewTess").  It is a good idea to read that chapter before
       reading the rest of this document.

       As much as possible, the POGL implementation of the tessellation functions tries to remain
       faithful to the OpenGL specification.  Where it doesn't match exactly, POGL follows the
       spirit of the specification, but offloads what it can to c based implementations.

       Tessellation functions are safe to call during drawlist creation.  It is advisable to use
       drawlists, or to store the generated polygon data into OpenGL::Array objects as these
       methods offer faster redraws.

FUNCTIONS

       "gluNewTess"
               my $tess = gluNewTess();

           Returns a reference that can be passed to the remaining tesselation functions.

           Note: this isn't the c-reference returned by the normal gluNewTess() c function, it is
           a struct which contains that reference as well as other members allowing callbacks to
           interface cleanly with the perl code.  This means that if you have loaded other
           c-libraries that use standard opengl tessellation, you will not be able to use this
           perl reference directly.

           The POGL implementation of gluNewTess() allows for two additional parameters to be
           passed.  The first is a boolean value indicating that default c callbacks and perl
           callbacks should be passed rgba color data.  The second is a boolean value indicating
           that xyz normal data should be passed.  Eventually one additional flag indicating that
           texture data should be passed will be added as well.

               my $tess = gluNewTess();
               # gluTessVertex_p should be passed only x,y,z vertex data
               # as in gluTessVertex_p($tess, $x, $y, $z);

               my $tess = gluNewTess('do_colors');
               # gluTessVertex_p should be passed x,y,z AND r,g,b,a vertex data
               # as in gluTessVertex_p($tess, $x, $y, $z, $r, $g, $b, $a);

               my $tess = gluNewTess('do_colors', 'do_normals');
               # gluTessVertex_p should be passed x,y,z AND r,g,b,a AND nx,ny,nz vertex data
               # as in gluTessVertex_p($tess, $x, $y, $z, $r, $g, $b, $a, $nx, $ny, $nz);

               my $tess = gluNewTess(undef, 'do_normals');
               # gluTessVertex_p should be passed x,y,z AND nx,ny,nz vertex data (no colors)
               # as in gluTessVertex_p($tess, $x, $y, $z, $nx, $ny, $nz);

           Any true value can be passed in place of 'do_colors' and 'do_normals' though using
           'do_colors' and 'do_normals' acts as documentation.

           Behavior in these modes will be discussed further for functions to which they apply.

       "gluDeleteTess"
               gluDeleteTess($tess);

           This deletes the tessellation structure and frees up any remaining associated memory.

       "gluTessCallback"
              gluTessCallback($tess, GLU_TESS_BEGIN, 'DEFAULT');

              gluTessCallback($tess, GLU_TESS_BEGIN, \&glBegin);

              gluTessCallback($tess, GLU_TESS_BEGIN, sub { my $enum = shift; glBegin($enum) });

              gluTessCallback($tess, GLU_TESS_BEGIN);  # unsets current handler

           Registers handlers for each of the tessellation callback types.  Takes a tessellation
           reference generated by gluNewTess, a type, and a coderef or the word 'DEFAULT'.  If
           the word 'DEFAULT' is passed, a default c-level callback will be installed (which will
           be discussed for each callback).  If no 3rd argument is given, then any handler
           currently set will be removed.  Valid callback types are

               GLU_TESS_BEGIN
               GLU_TESS_END
               GLU_TESS_VERTEX
               GLU_TESS_COMBINE
               GLU_TESS_ERROR
               GLU_TESS_EDGE_FLAG

               GLU_TESS_BEGIN_DATA
               GLU_TESS_END_DATA
               GLU_TESS_VERTEX_DATA
               GLU_TESS_COMBINE_DATA
               GLU_TESS_ERROR_DATA
               GLU_TESS_EDGE_FLAG_DATA

           These types and their passed parameters will be discussed in the CALLBACKS section.

           The types ending with "_DATA" are similar to their non-_DATA counterpart, but when
           called are passed the option $polygon_data that can be set during gluTessBeginPolygon.

       "gluTessBeginPolygon"
               gluTessBeginPolygon($tess);

               gluTessBeginPolygon($tess, $polygon_data);

           Begins the tessellation transaction.  It must eventually be ended with a
           gluTessEndPolygon before the tessellator will normally begin work.

           An optional second argument can be passed which can be any perl scalar or reference.
           If a callback is registered using a type ending in _DATA, this perl scalar or
           reference will be passed as an additional argument to that callback.

               gluTessCallback($tess, GLU_TESS_END_DATA, sub {
                   my $polygon_data = shift;
                   glEnd();
                   print "glEnd: (".($polygon_data->[2] eq 8 ? "YES" : "NO").")\n";
               });

               gluTessBeginPoly($tess, [6,7,8]); # arrayref will be passed to _DATA callbacks

           A sample Object Oriented tesselation sample listed at the end of this document makes
           use of this "opaque" polygon data.

       "gluTessEndPolygon"
               gluTessEndPolygon($tess);

           Finishes the tessellation transaction, which normally will immediately fire the
           necessary callbacks generated by the tessellation process.  Once finished, it cleans
           up any accumulated temporary vertice data.

       "gluTessBeginContour"
               gluTessBeginContour($tess);

           Starts a new contour of the tessellation of the current polygon.  Please read the
           OpenGL documentation, and red book chapter on tessellation for more help on when to
           use different contours.  Should eventually be followed by a gluTessEndContour call.

           (At a high level, tessellated polygons may have windows and multiple separate
           portions.  Each inner and outer border of these portions should be represented by a
           different contour.)

       "gluTessVertex_p"
               gluTessVertex_p($tess, $x, $y, $z);

               gluTessVertex_p($tess, $x, $y, $z, $vertex_data);

           Adds a vertex to the current contour of the current polygon being tessellated.

           If the vertex callback type is set to GLU_TESS_VERTEX, the optional $vertex_data
           argument will be passed to the vertex callback, and to the combine callback (if
           GLU_TESS_VERTEX_DATA is used, then the $polygon_data passed to gluTessBeginPolygon
           will be passed instead).  This optional opaque vertex data can be any perl scalar or
           reference and can be used to pass useful information along during the tessellation
           process.

           If the 'do_colors' or 'do_normals' parameters were passed to gluNewTess, then those
           additional properties MUST be passed as additional arguments.

               # my $tess = gluNewTess('do_colors');
               gluTessVertex_p($tess, $x, $y, $z, $r, $g, $b, $a);
               gluTessVertex_p($tess, $x, $y, $z, $r, $g, $b, $a, $vertex_data);

               # my $tess = gluNewTess('do_colors', 'do_normals');
               gluTessVertex_p($tess, $x, $y, $z, $r, $g, $b, $a, $nx, $ny, $nz);
               gluTessVertex_p($tess, $x, $y, $z, $r, $g, $b, $a, $nx, $ny, $nz, $vertex_data);

               # my $tess = gluNewTess(undef, 'do_normals');
               gluTessVertex_p($tess, $x, $y, $z, $nx, $ny, $nz);
               gluTessVertex_p($tess, $x, $y, $z, $nx, $ny, $nz, $vertex_data);

CALLBACKS

       All of the callbacks support a 'DEFAULT' handler that can be installed by passing the word
       'DEFAULT' in place of the callback code reference.  The DEFAULT c implementations are
       there to avoid needing to round trip out to perl.  The defaults employed are described for
       each of the callback types.

       With the exception of the COMBINE callback, return values from callbacks are discarded.

       "GLU_TESS_BEGIN"
              gluTessCallback($tess, GLU_TESS_BEGIN, 'DEFAULT');

              gluTessCallback($tess, GLU_TESS_BEGIN, \&glBegin);

              gluTessCallback($tess, GLU_TESS_BEGIN, sub {
                  my $enum = shift;
                  glBegin($enum);
              });

           The 'DEFAULT' option installs a c-handler that calls the glBegin c function directly
           without round-tripping out to perl.

           If $polygon_data was set during gluTessBeginPolygon, it is discarded.

       "GLU_TESS_BEGIN_DATA"
           Similar to GLU_TESS_BEGIN but will be passed optional $polygon_data set in
           gluTessBeginPolygon if any.  The 'DEFAULT' handler will ignore this data.

              gluTessCallback($tess, GLU_TESS_BEGIN_DATA, sub {
                  my ($enum, $polygon_data) = @_;
                  glBegin($enum);
                  print "glBegin - and I received polygon_data\n" if $polygon_data;
              });

       "GLU_TESS_END"
              gluTessCallback($tess, GLU_TESS_END, 'DEFAULT');

              gluTessCallback($tess, GLU_TESS_END, \&glEnd);

              gluTessCallback($tess, GLU_TESS_END, sub { glEnd() });

           The 'DEFAULT' option installs a c-handler that calls the glEnd c function directly
           without round-tripping out to perl.

           If $polygon_data was set during gluTessBeginPolygon, it is discarded.

       "GLU_TESS_END_DATA"
           Similar to GLU_TESS_END but will be passed optional $polygon_data set in
           gluTessBeginPolygon if any.  The 'DEFAULT' handler will ignore this data.

              gluTessCallback($tess, GLU_TESS_END_DATA, sub {
                  my ($polygon_data) = @_;
                  glEnd();
                  print "glEnd - and I received polygon_data\n" if $polygon_data;
              });

       "GLU_TESS_VERTEX"
           The GLU_TESS_VERTEX callback handler has slightly different behavior depending on how
           gluNewTess was called.  The optional behaviors allow for sane default processing of
           colors and normals without needing to roundtrip out to perl.

              my $tess = gluNewTess();

              gluTessCallback($tess, GLU_TESS_VERTEX, 'DEFAULT');

              # the following will break if vertex_data is passed to gluTessVertex_p
              gluTessCallback($tess, GLU_TESS_VERTEX, \&glVertex3f);

              gluTessCallback($tess, GLU_TESS_VERTEX, sub {
                  my ($x, $y, $z) = @_;
                  glVertex3f($x, $y, $z);
              });

              # you can also pass vertex_data to gluTessVertex_p
              gluTessCallback($tess, GLU_TESS_VERTEX, sub {
                  my ($x, $y, $z, $vertex_data) = @_;
                  glVertex3f($x, $y, $z);
                  print "glVertex - and I received vertex_data\n" if $vertex_data;
              });

           The 'DEFAULT' option installs a c-handler that calls the glVertex c function directly
           without round-tripping out to perl.  The DEFAULT handler discards any polygon_data or
           vertex_data.

           IF $vertex_data was set during gluTessVertex_p it will be passed as the final
           argument.

           If gluNewTess was passed 'do_colors' then the GLU_TESS_VERTEX callback will also be
           passed the rgba information.  The 'DEFAULT' option will pass the color information to
           glColor4f before calling glVertex3f.

              my $tess = gluNewTess('do_colors');

              gluTessCallback($tess, GLU_TESS_VERTEX, sub {
                  my ($x, $y, $z, $r, $g, $b, $a, $vertex_data) = @_;
                  glColor4f($r, $g, $b, $a);
                  glVertex3f($x, $y, $z);
              });

           If gluNewTess was passed 'do_normals' then the GLU_TESS_VERTEX callback will also be
           passed the normal x,y,z information.  The 'DEFAULT' option will pass the normal
           information to glNormal3f before calling glVertex3f.

              my $tess = gluNewTess('do_colors', 'do_normals');

              gluTessCallback($tess, GLU_TESS_VERTEX, sub {
                  my ($x, $y, $z, $r, $g, $b, $a, $nx, $ny, $nz, $vertex_data) = @_;
                  glColor4f($r, $g, $b, $a);
                  glNormalf($nx, $ny, $nz);
                  glVertex3f($x, $y, $z);
              });

              # OR

              my $tess = gluNewTess(undef, 'do_normals');

              gluTessCallback($tess, GLU_TESS_VERTEX, sub {
                  my ($x, $y, $z, $nx, $ny, $nz, $vertex_data) = @_;
                  glNormalf($nx, $ny, $nz);
                  glVertex3f($x, $y, $z);
              });

           In all cases, any optional vertex_data will be passed as the final argument.

       "GLU_TESS_VERTEX_DATA"
           Similar to GLU_TESS_VERTEX but will be passed optional $polygon_data set in
           gluTessBeginPolygon (if any) rather than the optional $vertex_data passed to
           gluTessVertex_p.  The 'DEFAULT' handler will ignore this data.

              gluTessCallback($tess, GLU_TESS_VERTEX_DATA, sub {
                  my ($x, $y, $z, $vertex_data) = @_;
                  glVertex3f($x, $y, $z);
                  print "glVertex - and I received vertex_data\n" if $vertex_data;
              });

       "GLU_TESS_COMBINE"
              gluTessCallback($tess, GLU_TESS_COMBINE, 'DEFAULT');
              # works with gluTessCallback($tess, GLU_TESS_VERTEX, 'DEFAULT');

              # OR

              # the following callback is valid for gluNewTess() (no do_colors or do_normals)
              # using gluTessVertex_p($tess, $x, $y, $z);
              my $tess = gluNewTess();
              gluTessCallback($tess, GLU_TESS_COMBINE, sub {
                  my ($x, $y, $z,           # new vertex location
                      $v0, $v1, $v2, $v3,   # border vertex arrayrefs
                      $w0, $w1, $w2, $w3,   # border vertex weights
                      $polygon_data) = @_;  # optional data passed to gluTessBeginPolygon
                  return ($x, $y, $z);
              });
              # works with gluTessCallback($tess, GLU_TESS_VERTEX, 'DEFAULT');

              # OR

              # the following callback is valid for gluNewTess() when vertex data is passed
              # using gluTessVertex_p($tess, $x, $y, $z, [$r, $g, $b, $a]);
              # The DEFAULT callback cannot automatically proceess this type of data
              # but passing data to a custom handler this way could handle any arbitrary data passed to it
              my $tess = gluNewTess();
              use constant _r => 0;
              use constant _g => 1;
              use constant _b => 2;
              use constant _a => 3;
              gluTessCallback($tess, GLU_TESS_COMBINE, sub {
                  my ($x, $y, $z,           # new vertex location
                      $v0, $v1, $v2, $v3,   # border vertex arrayrefs
                      $w0, $w1, $w2, $w3,   # border vertex weights
                      $polygon_data) = @_;  # optional data passed to gluTessBeginPolygon

                  # $v0 will contain [$x, $y, $z, [$r, $g, $b, $a]]
                  my @rgba = map {$_->[3]} $v0, $v1, $v2, $v3;

                  # generate a point with color weighted from the surrounding vertices
                  # then return that color information in the same way we received it (an rgba arrayref)
                  return (
                      $x, $y, $z,
                      [$w0*$rgba[0]->[_r] + $w1*$rgba[1]->[_r] + $w2*$rgba[2]->[_r] + $w3*$rgba[3]->[_r],
                       $w0*$rgba[0]->[_g] + $w1*$rgba[1]->[_g] + $w2*$rgba[2]->[_g] + $w3*$rgba[3]->[_g],
                       $w0*$rgba[0]->[_b] + $w1*$rgba[1]->[_b] + $w2*$rgba[2]->[_b] + $w3*$rgba[3]->[_b],
                       $w0*$rgba[0]->[_a] + $w1*$rgba[1]->[_a] + $w2*$rgba[2]->[_a] + $w3*$rgba[3]->[_a]],
                      );
              });
              # works with gluTessCallback($tess, GLU_TESS_VERTEX, sub {
              #    my ($x, $y, $z, $rgba) = @_;
              #    glColor4f(@$rgba);
              #    glVertex3f($x, $y, $z);
              # });

              # OR

              # the following callback is valid for gluNewTess('do_colors')
              # using gluTessVertex_p($tess, $x, $y, $z, $r, $g, $b, $a);
              # the DEFAULT callback COULD automatically proceess this type of data as well if additional vertex data is not passed
              my $tess = gluNewTess('do_colors');
              use constant _r => 3;
              use constant _g => 4;
              use constant _b => 5;
              use constant _a => 6;
              gluTessCallback($tess, GLU_TESS_COMBINE, sub {
                  my ($x, $y, $z,           # new vertex location
                      $v0, $v1, $v2, $v3,   # border vertex arrayrefs
                      $w0, $w1, $w2, $w3,   # border vertex weights
                      $polygon_data) = @_;  # optional data passed to gluTessBeginPolygon

                  # $v0 will contain [$x, $y, $z, $r, $g, $b, $a]

                  return ( # generate a point with color weighted from the surrounding vertices
                      $x, $y, $z,
                      $w0*$v0->[_r] + $w1*$v1->[_r] + $w2*$v2->[_r] + $w3*$v3->[_r],
                      $w0*$v0->[_g] + $w1*$v1->[_g] + $w2*$v2->[_g] + $w3*$v3->[_g],
                      $w0*$v0->[_b] + $w1*$v1->[_b] + $w2*$v2->[_b] + $w3*$v3->[_b],
                      $w0*$v0->[_a] + $w1*$v1->[_a] + $w2*$v2->[_a] + $w3*$v3->[_a],
                      ($v0->[7] || $v1->[7] || $v2->[7] || $v3->[7]), # if we received vertex data - return some for the new vertex
                      );
              });
              # works with gluTessCallback($tess, GLU_TESS_VERTEX, 'DEFAULT');
              # OR
              # works with gluTessCallback($tess, GLU_TESS_VERTEX, sub {
              #    my ($x, $y, $z, $r, $g, $b, $a, $vertex_data) = @_;
              #    glColor4f($r, $g, $b, $a);
              #    glVertex3f($x, $y, $z);
              # });

           The combine callback is called if the tessellator decides a new vertex is needed.
           This will happen with self intersecting polygons.  In this case, the COMBINE callback
           can be used to interpolate appropriate values for normals, and colors, or for any
           desired information.

           The combine callback will be passed the following:

           "$x, $y, $z"
               The x y and z coordinates of the new vertex being created.

           "$v0, $v1, $v2, $v3"
               Arrayrefs of vertex information for the vertices bordering this new vertex (the
               ones that caused the new vertex to be created).

               By default if gluNewTess() is called, these arrayrefs will be passed:

                    my ($x, $y, $z, $vertex_data) = @$v0;
                    # received from gluTessVertex_p($tess, $x, $y, $z, $vertex_data);

               If gluNewTess('do_colors') is called, the following will be passed:

                    my ($x, $y, $z, $r, $g, $b, $a, $vertex_data) = @$v0;
                    # received from gluTessVertex_p($tess, $x, $y, $z, $r, $g, $b, $a, $vertex_data);

               If gluNewTess('do_colors', 'do_normals') is called, the following will be passed:

                    my ($x, $y, $z, $r, $g, $b, $a, $nx, $ny, $nz, $vertex_data) = @$v0;
                    # received from gluTessVertex_p($tess, $x, $y, $z, $r, $g, $b, $a, $nx, $ny, $nz, $vertex_data);

               If gluNewTess(undef, 'do_normals') is called, the following will be passed:

                    my ($x, $y, $z, $nx, $ny, $nz, $vertex_data) = @$v0;
                    # received from gluTessVertex_p($tess, $x, $y, $z, $nx, $ny, $nz, $vertex_data);

               In all cases, the data returned by the COMBINE callback should be in the same
               format that each of the vertices are in when passed into the COMBINE callback.

           "$w0, $w1, $w2, $w3"
               Weights of the participating vertices (weight $w0 corresponds to vertex $v0).

           "optional $polygon_data"
               Any optional data passed to gluTessBeginPolygon.  Normally this would only be
               passed to GLU_TESS_COMBINE_DATA, but GLU_TESS_COMBINE_DATA and GLU_TESS_COMBINE
               share the same code implementation.

       "GLU_TESS_COMBINE_DATA"
           Identical in function to the GLU_TESS_COMBINE handler.  They use the same callback
           implementation.

       "GLU_TESS_ERROR"
              gluTessCallback($tess, GLU_TESS_ERROR, 'DEFAULT');

              gluTessCallback($tess, GLU_TESS_ERROR, \&glEdgeFlag);

              gluTessCallback($tess, GLU_TESS_ERROR, sub {
                  my $errno = shift;
                  my $err = gluErrorString($errno);
                  warn "Received a glu tess error ($errno - $err)\n";
               });

           The 'DEFAULT' option installs a c-handler that warns with the appropriate
           gluErrorString.

           If $polygon_data was set during gluTessBeginPolygon, it is discarded.

       "GLU_TESS_ERROR_DATA"
           Similar to GLU_TESS_ERROR but will be passed optional $polygon_data set in
           gluTessBeginPolygon if any.  The 'DEFAULT' handler will ignore this data.

              gluTessCallback($tess, GLU_TESS_ERROR_DATA, sub {
                  my ($errno, $polygon_data) = @_;
                  my $err = gluErrorString($errno);
                  warn "Received a glu tess error ($errno - $err)\n";
                  warn "And I received polygon_data\n" if $polygon_data;
              });

       "GLU_TESS_EDGE_FLAG"
              gluTessCallback($tess, GLU_TESS_EDGE_FLAG, 'DEFAULT');

              gluTessCallback($tess, GLU_TESS_EDGE_FLAG, \&glEdgeFlag);

              gluTessCallback($tess, GLU_TESS_EDGE_FLAG, sub {
                  my ($flag) = @_;
                  glEdgeFlag($flag);
               });

           The 'DEFAULT' option installs a c-handler that calls the glEdgeFlag c function
           directly without round-tripping out to perl.

           If $polygon_data was set during gluTessBeginPolygon, it is discarded.

       "GLU_TESS_EDGE_FLAG_DATA"
           Similar to GLU_TESS_EDGE_FLAG but will be passed $polygon_data set in
           gluTessBeginPolygon if any.  The 'DEFAULT' handler will ignore this data.

              gluTessCallback($tess, GLU_TESS_EDGE_FLAG_DATA, sub {
                  my ($flag, $polygon_data) = @_;
                  glEdgeFlag($flag);
                  print "glEdgeFlag - and I received polygon_data\n" if $polygon_data;
              });

Example: Basic Arrowhead

           use OpenGL qw(:all);

           glutInit();
           glutInitWindowSize(501, 501);
           glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
           glutCreateWindow("Tessellation");
           glMatrixMode(GL_PROJECTION());
           glLoadIdentity();
           glOrtho(-250,250,-250,250,-1.0,1.0);
           glMatrixMode(GL_MODELVIEW);

           my $view_triangles = 1; # set to zero to show polygon
           glPolygonMode(GL_FRONT_AND_BACK, GL_LINE) if $view_triangles;

           glutDisplayFunc(sub {
               glColor3f(1,1,1);

               my $tess = gluNewTess();
               gluTessCallback($tess, GLU_TESS_BEGIN,     'DEFAULT');
               gluTessCallback($tess, GLU_TESS_END,       'DEFAULT');
               gluTessCallback($tess, GLU_TESS_VERTEX,    'DEFAULT');
               gluTessCallback($tess, GLU_TESS_COMBINE,   'DEFAULT');
               gluTessCallback($tess, GLU_TESS_ERROR,     'DEFAULT');
               gluTessCallback($tess, GLU_TESS_EDGE_FLAG, 'DEFAULT') if ! $view_triangles;
               gluTessBeginPolygon($tess);
               gluTessBeginContour($tess);

               gluTessVertex_p($tess, 0,    200,  0);
               gluTessVertex_p($tess, 150,  -200, 0);
               gluTessVertex_p($tess, 0,    -100, 0);
               gluTessVertex_p($tess, -150, -200, 0);

               gluTessEndContour($tess);
               gluTessEndPolygon($tess);
               gluDeleteTess($tess);

               glutSwapBuffers();
           });

           glutMainLoop();

Example: Multiple contours

           use OpenGL qw(:all);

           glutInit();
           glutInitWindowSize(501, 501);
           glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
           glutCreateWindow("Tessellation");
           glMatrixMode(GL_PROJECTION());
           glLoadIdentity();
           glOrtho(-250,250,-250,250,-1.0,1.0);
           glMatrixMode(GL_MODELVIEW);

           my $view_triangles = 1; # set to zero to show polygon
           glPolygonMode(GL_FRONT_AND_BACK, GL_LINE) if $view_triangles;

           glutDisplayFunc(sub {
               glColor3f(1,1,1);
               my $v = [[[125,0,0], [150,150,0], [0,125,0], [-150,150,0],
                         [-125,0,0], [-150,-150,0], [0,-125,0], [150,-150,0], [125,0,0]],
                        [[75,0,0], [100,100,0], [0,75,0], [-100,100,0],
                         [-75,0,0], [-100,-100,0], [0,-75,0], [100,-100,0], [75,0,0]]
                       ];

               my $tess = gluNewTess();
               gluTessCallback($tess, GLU_TESS_BEGIN,     'DEFAULT');
               gluTessCallback($tess, GLU_TESS_END,       'DEFAULT');
               gluTessCallback($tess, GLU_TESS_VERTEX,    'DEFAULT');
               gluTessCallback($tess, GLU_TESS_COMBINE,   'DEFAULT');
               gluTessCallback($tess, GLU_TESS_ERROR,     'DEFAULT');
               gluTessCallback($tess, GLU_TESS_EDGE_FLAG, 'DEFAULT') if ! $view_triangles;
               gluTessBeginPolygon($tess);
               foreach (@$v) {
                   gluTessBeginContour($tess);
                   foreach (@$_) {
                       gluTessVertex_p($tess, @$_);
                   }
                   gluTessEndContour($tess);
               }
               gluTessEndPolygon($tess);
               gluDeleteTess($tess);

               glutSwapBuffers();
           });

           glutMainLoop();

Example: Sample OO Tessellation interface using polygon_data

           use OpenGL qw(:all);

           glutInit();
           glutInitWindowSize(501, 501);
           glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
           glutCreateWindow("Tessellation");
           glMatrixMode(GL_PROJECTION());
           glLoadIdentity();
           glOrtho(-250,250,-250,250,-1.0,1.0);
           glMatrixMode(GL_MODELVIEW);

           my $view_triangles = 0;
           glPolygonMode(GL_FRONT_AND_BACK, GL_LINE) if $view_triangles;

           glutDisplayFunc(sub {
               glColor3f(1,1,1);
               my $v = [[[125,0,0], [150,150,0, 0,1,0], [0,125,0], [-150,150,0, 1,0,0],
                         [-125,0,0], [-150,-150,0, 0,0,1], [0,-125,0], [150,-150,0, 1,1,0], [125,0,0]],
                        [[75,0,0], [100,100,0], [0,75,0], [-100,100,0],
                         [-75,0,0], [-100,-100,0], [0,-75,0], [100,-100,0], [75,0,0]]
                       ];

               OpenGL::Tess->new(do_colors => 1, no_edge_flag => $view_triangles)->draw_contours(@$v);

               glutSwapBuffers();
           });

           glutMainLoop();

           ###----------------------------------------------------------------###

           package OpenGL::Tess;

           # Sample object oriented Tessellator
           # OpenGL::Tess->new(do_colors => 1, no_edge_flag => $view_triangles)->draw_contours(@$v);

           use strict;

           sub new {
               my $class = shift;
               my $self  = bless {@_}, $class;
               my $tess = $self->{'_tess'} = OpenGL::gluNewTess($self->do_colors);
               for my $cb (qw(begin end vertex combine error edge_flag)) {
                   my $enum = OpenGL->can("GLU_TESS_\U${cb}_DATA") || die "Couldn't find callback for $cb";
                   my $name = "_$cb";
                   OpenGL::gluTessCallback($tess, $enum->(), sub { $_[-1]->$name(@_) });
               }
               return $self;
           }

           sub DESTROY {
               my $tess = shift->{'_tess'};
               OpenGL::gluDeleteTess($tess) if $tess;
           }

           sub tess {
               my $self = shift;
               return $self->{'_tess'} || die "Missing tess";
           }

           sub do_colors { shift->{'do_colors'} }

           sub begin_polygon {
               my $self = shift;
               my $tess = $self->tess;
               # self will be passed as last arg ([-1]) to all callbacks as opaque polygon data
               return OpenGL::gluTessBeginPolygon($tess, $self);
           }

           sub end_polygon   { OpenGL::gluTessEndPolygon(  shift->tess) }
           sub begin_contour { OpenGL::gluTessBeginContour(shift->tess) }
           sub end_contour   { OpenGL::gluTessEndContour(  shift->tess) }

           sub draw_contours {
               my $self = shift;
               $self->begin_polygon;
               foreach my $c (@_) {
                   $self->begin_contour;
                   $self->add_vertex(@$_) for @$c;
                   $self->end_contour;
               }
               $self->end_polygon;
           }

           sub add_vertex {
               my $self = shift;
               die 'Usage $self->add_vertex($x,$y,$z)' if @_ < 3;
               if ($self->do_colors) {
                   push @_, 1 for @_ .. 6;
                   OpenGL::gluTessVertex_p($self->tess, @_[0..6]);
               } else {
                   OpenGL::gluTessVertex_p($self->tess, @_[0..3]);
               }
           }

           sub _begin {
               my ($self, $enum) = @_;
               OpenGL::glBegin($enum);
           }

           sub _end { OpenGL::glEnd() }

           sub _vertex {
               my ($self, $x, $y, $z, $r, $g, $b, $a) = @_;
               OpenGL::glColor4f($r, $g, $b, $a) if $self->do_colors;
               OpenGL::glVertex3f($x, $y, $z);
           }

           sub _edge_flag {
               my ($self, $flag) = @_;
               return if $self->{'no_edge_flag'};
               OpenGL::glEdgeFlag($flag);
           }

           sub _error {
               my ($self, $errno) = @_;
               warn __PACKAGE__ ." error: ".OpenGL::gluErrorString($errno);
           }

           sub _combine {
               my ($self, $x, $y, $z, $v0, $v1, $v2, $v3, $w0, $w1, $w2, $w3) = @_;
               return ($x, $y, $z) if !$self->do_colors;
               return ($x, $y, $z,
                       $w0*$v0->[3] + $w1*$v1->[3] + $w2*$v2->[3] + $w3*$v3->[3],
                       $w0*$v0->[4] + $w1*$v1->[4] + $w2*$v2->[4] + $w3*$v3->[4],
                       $w0*$v0->[5] + $w1*$v1->[5] + $w2*$v2->[5] + $w3*$v3->[5],
                       $w0*$v0->[6] + $w1*$v1->[6] + $w2*$v2->[6] + $w3*$v3->[6]);
           }

           1;

AUTHOR

         Paul Seamons - paul AT seamons dot com - 2011