#/*
# * Copyright (c) 1993-1997, Silicon Graphics, Inc.
# * ALL RIGHTS RESERVED 
# * Permission to use, copy, modify, and distribute this software for 
# * any purpose and without fee is hereby granted, provided that the above
# * copyright notice appear in all copies and that both the copyright notice
# * and this permission notice appear in supporting documentation, and that 
# * the name of Silicon Graphics, Inc. not be used in advertising
# * or publicity pertaining to distribution of the software without specific,
# * written prior permission. 
# *
# * THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU "AS-IS"
# * AND WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR OTHERWISE,
# * INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY OR
# * FITNESS FOR A PARTICULAR PURPOSE.  IN NO EVENT SHALL SILICON
# * GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT,
# * SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY
# * KIND, OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION,
# * LOSS OF PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF
# * THIRD PARTIES, WHETHER OR NOT SILICON GRAPHICS, INC.  HAS BEEN
# * ADVISED OF THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON
# * ANY THEORY OF LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE
# * POSSESSION, USE OR PERFORMANCE OF THIS SOFTWARE.
# * 
# * 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# * Unpublished-- rights reserved under the copyright laws of the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.
# */
#
#/*
# *  alpha.c
# *  This program draws several overlapping filled polygons
# *  to demonstrate the effect order has on alpha blending results.
# *  Use the 't' key to toggle the order of drawing polygons.
# */

require "opengl"
require "glut"
require "mathn"

$leftFirst = GL::TRUE;

#/*  Initialize alpha blending function.
# */
def init
   GL.Enable(GL::BLEND);
   GL.BlendFunc(GL::SRC_ALPHA, GL::ONE_MINUS_SRC_ALPHA);
   GL.ShadeModel(GL::FLAT);
   GL.ClearColor(0.0, 0.0, 0.0, 0.0);
end

def drawLeftTriangle
   #/* draw yellow triangle on LHS of screen */

   GL.Begin(GL::TRIANGLES);
      GL.Color(1.0, 1.0, 0.0, 0.75);
      GL.Vertex(0.1, 0.9, 0.0); 
      GL.Vertex(0.1, 0.1, 0.0); 
      GL.Vertex(0.7, 0.5, 0.0); 
   GL.End();
end

def drawRightTriangle
   #/* draw cyan triangle on RHS of screen */

   GL.Begin(GL::TRIANGLES);
      GL.Color(0.0, 1.0, 1.0, 0.75);
      GL.Vertex(0.9, 0.9, 0.0); 
      GL.Vertex(0.3, 0.5, 0.0); 
      GL.Vertex(0.9, 0.1, 0.0); 
   GL.End();
end

display = Proc.new {
   GL.Clear(GL::COLOR_BUFFER_BIT);

   if ($leftFirst)
      drawLeftTriangle();
      drawRightTriangle();
   else
      drawRightTriangle();
      drawLeftTriangle();
   end

   GL.Flush();
}

reshape = Proc.new {|w, h|
   GL.Viewport(0, 0,  w, h);
   GL.MatrixMode(GL::PROJECTION);
   GL.LoadIdentity();
   if (w <= h) 
      GLU.Ortho2D(0.0, 1.0, 0.0, 1.0*h/w);
   else 
      GLU.Ortho2D(0.0, 1.0*w/h, 0.0, 1.0);
   end
}

# /* ARGSUSED1 */
keyboard = Proc.new {|key, x, y|
   case (key)
      when 't'[0],'T'[0]
         $leftFirst = !$leftFirst;
         GLUT.PostRedisplay();	
      when 27  #  /*  Escape key  */
         exit(0);
   end
}

#/*  Main Loop
# *  Open window with initial window size, title bar, 
# *  RGBA display mode, and handle input events.
# */
#int main(int argc, char** argv)
#{
   GLUT.Init
   GLUT.InitDisplayMode(GLUT::SINGLE | GLUT::RGB);
   GLUT.InitWindowSize(200, 200);
   GLUT.CreateWindow($0);
   init();
   GLUT.ReshapeFunc(reshape);
   GLUT.KeyboardFunc(keyboard);
   GLUT.DisplayFunc(display);
   GLUT.MainLoop();
