#
# Copyright (c) 1993-1997, Silicon Graphics, Inc.
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# US Government Users Restricted Rights
# Use, duplication, or disclosure by the Government is subject to
# restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
# (c)(1)(ii) of the Rights in Technical Data and Computer Software
# clause at DFARS 252.227-7013 and/or in similar or successor
# clauses in the FAR or the DOD or NASA FAR Supplement.
# Unpublished-- rights reserved under the copyright laws of the
# United States.  Contractor/manufacturer is Silicon Graphics,
# Inc., 2011 N.  Shoreline Blvd., Mountain View, CA 94039-7311.
#
# OpenGL(R) is a registered trademark of Silicon Graphics, Inc.
#
# tess.c
# This program demonstrates polygon tessellation.
# Two tesselated objects are drawn.  The first is a
# rectangle with a triangular hole.  The second is a
# smooth shaded, self-intersecting star.
#
# Note the exterior rectangle is drawn with its vertices
# in counter-clockwise order, but its interior clockwise.
# Note the combineCallback is needed for the self-intersecting
# star.  Also note that removing the TessProperty for the
# star will make the interior unshaded (WINDING_ODD).
require 'opengl'
require 'glu'
require 'glut'
include Gl,Glu,Glut

$startList = nil

display = proc do
  glClear(GL_COLOR_BUFFER_BIT)
  glColor(1.0, 1.0, 1.0)
  glCallList($startList)
  glCallList($startList + 1)
  glutSwapBuffers()
end

$beginCallback = proc do |which|
  glBegin(which)
end

$errorCallback = proc do |errorCode|
  print "Tessellation Error: #{gluErrorString(errorCode)}"
  exit(0)
end

$endCallback = proc do
  glEnd()
end

$vertexCallback = proc do |vertex|
  glColor(vertex[3], vertex[4], vertex[5])
  glVertex(vertex[0], vertex[1], vertex[2])
end

# combineCallback is used to create a new vertex when edges
# intersect.  coordinate location is trivial to calculate,
# but weight[4] may be used to average color, normal, or texture
# coordinate data.  In this program, color is weighted.
$combineCallback = proc do |coords, vertex_data, weight|
  vertex = []
  vertex[0] = coords[0]
  vertex[1] = coords[1]
  vertex[2] = coords[2]
  for i in 3...6
    vertex[i] = weight[0] * vertex_data[0][i] + weight[1] * vertex_data[1][i] + weight[2] * vertex_data[2][i] + weight[3] * vertex_data[3][i]
  end
  vertex
end

def init
  rect = [[50.0, 50.0, 0.0],
    [200.0, 50.0, 0.0],
    [200.0, 200.0, 0.0],
    [50.0, 200.0, 0.0]]
  tri = [[75.0, 75.0, 0.0],
    [125.0, 175.0, 0.0],
    [175.0, 75.0, 0.0]]
  star= [[250.0, 50.0, 0.0, 1.0, 0.0, 1.0],
    [325.0, 200.0, 0.0, 1.0, 1.0, 0.0],
    [400.0, 50.0, 0.0, 0.0, 1.0, 1.0],
    [250.0, 150.0, 0.0, 1.0, 0.0, 0.0],
    [400.0, 150.0, 0.0, 0.0, 1.0, 0.0]]

  glClearColor(0.0, 0.0, 0.0, 0.0)

  $startList = glGenLists(2)

  tobj = gluNewTess()
  gluTessCallback(tobj, GLU_TESS_VERTEX, proc do |v| glVertex(v) end )
  gluTessCallback(tobj, GLU_TESS_BEGIN, $beginCallback)
  gluTessCallback(tobj, GLU_TESS_END, $endCallback)
  gluTessCallback(tobj, GLU_TESS_ERROR, $errorCallback)

  # rectangle with triangular hole inside
  glNewList($startList, GL_COMPILE)
  glShadeModel(GL_FLAT)
  gluTessBeginPolygon(tobj, nil)
  gluTessBeginContour(tobj)
  gluTessVertex(tobj, rect[0], rect[0])
  gluTessVertex(tobj, rect[1], rect[1])
  gluTessVertex(tobj, rect[2], rect[2])
  gluTessVertex(tobj, rect[3], rect[3])
  gluTessEndContour(tobj)
  gluTessBeginContour(tobj)
  gluTessVertex(tobj, tri[0], tri[0])
  gluTessVertex(tobj, tri[1], tri[1])
  gluTessVertex(tobj, tri[2], tri[2])
  gluTessEndContour(tobj)
  gluTessEndPolygon(tobj)
  glEndList()

  gluTessCallback(tobj, GLU_TESS_VERTEX, $vertexCallback)
  gluTessCallback(tobj, GLU_TESS_BEGIN, $beginCallback)
  gluTessCallback(tobj, GLU_TESS_END, $endCallback)
  gluTessCallback(tobj, GLU_TESS_ERROR, $errorCallback)
  gluTessCallback(tobj, GLU_TESS_COMBINE, $combineCallback)


# smooth shaded, self-intersecting star
  glNewList($startList + 1, GL_COMPILE)
  glShadeModel(GL_SMOOTH)
  gluTessProperty(tobj, GLU_TESS_WINDING_RULE, GLU_TESS_WINDING_POSITIVE)
  gluTessBeginPolygon(tobj, nil)
  gluTessBeginContour(tobj)
  gluTessVertex(tobj, star[0], star[0])
  gluTessVertex(tobj, star[1], star[1])
  gluTessVertex(tobj, star[2], star[2])
  gluTessVertex(tobj, star[3], star[3])
  gluTessVertex(tobj, star[4], star[4])
  gluTessEndContour(tobj)
  gluTessEndPolygon(tobj)
  glEndList()
  gluDeleteTess(tobj)
end

reshape = proc do |w, h|
  glViewport(0, 0, w, h)
  glMatrixMode(GL_PROJECTION)
  glLoadIdentity()
  gluOrtho2D(0.0, w, 0.0, h)
end

keyboard = proc do |key, x, y|
  case (key)
    when ?\e
      exit(0)
  end
end

glutInit()
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB)
glutInitWindowSize(500, 500)
glutInitWindowPosition(100, 100)
glutCreateWindow()
init()
glutDisplayFunc(display)
glutReshapeFunc(reshape)
glutKeyboardFunc(keyboard)
glutMainLoop()
