;; /*
;; * 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;; * Unpublished-- rights reserved under the copyright laws of the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.
;; */

(use srfi-1 utils gl glu glut srfi-4)

(define leftFirst gl:TRUE)
(define *args* (argv))

;; /*  Initialize alpha blending function.
;; */

(define (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))

(define (drawLeftTriangle)
   ;; /* draw yellow triangle on LHS of screen */

  (gl:Begin gl:TRIANGLES)
  (gl:Color4f 1.0 1.0 0.0 0.75)
  (gl:Vertex3f 0.1 0.9 0.0)
  (gl:Vertex3f 0.1 0.1 0.0)
  (gl:Vertex3f 0.7 0.5 0.0) 
  (gl:End))

(define (drawRightTriangle)
   ;; /* draw cyan triangle on RHS of screen */

  (gl:Begin gl:TRIANGLES)
  (gl:Color4f 0.0 1.0 1.0 0.75)
  (gl:Vertex3f 0.9 0.9 0.0) 
  (gl:Vertex3f 0.3 0.5 0.0)
  (gl:Vertex3f 0.9 0.1 0.0) 
  (gl:End))

(define (display)
  (gl:Clear gl:COLOR_BUFFER_BIT)
  (if leftFirst
      (begin
        (drawLeftTriangle)
        (drawRightTriangle))
      (begin
        (drawRightTriangle)
        (drawLeftTriangle)))
  (gl:Flush))

(define (reshape 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)))
      (glu:Ortho2D 0.0 (* 1.0 (/ w h)) 0.0 1.0)))

;; /* ARGSUSED1 */
(define (keyboard key x y)
  (case key
     ((#\t #\T)
      (set! leftFirst (not leftFirst))
      (glut:PostRedisplay))
     ((#\q)  ;; /*  Escape key  */ ** Changed to "q"
      (exit 0))))

;;  *  Open window with initial window size, title bar, 
;;  *  RGBA display mode, and handle input events.

;; (glut:Init)
(print "Use t to toggle drawing order of polygons and q to exit")
(glut:InitDisplayMode (+ glut:SINGLE glut:RGB))
(glut:InitWindowSize 200 200)
(glut:CreateWindow (list-ref *args* 1))
(init)
(glut:ReshapeFunc reshape)
(glut:KeyboardFunc keyboard)
(glut:DisplayFunc display)
(glut:MainLoop)