[Chicken-users] What should (POINTER VOID) be in opengl?

[Matthew Welland]

I'm trying to get tesselation to work and getting nowhere fast. My callbacks 
are not being called and I suspect I'm off target in more than one place. 
Anyhow for starters, what would I put for (POINTER VOID) in the following:

[procedure] (glu:TessBeginPolygon (POINTER GLUTESSELATOR) (POINTER VOID))

Here is the complete code I am trying to get to work, you can see I tried #f 
and at least the code runs but the callbacks never get called:
###################
(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))

;;
;; The simplest possible tesselation code...
;;

(define startList 1)

;; required callback routines
;;
(define (tcbBegin prim)
  (printf "tcbBegin ~A\n" prim)
  (gl:Begin prim))

(define (tbbVertex data)
  (printf "tbbVertex ~A\n" data)
  (gl:Vertex2dv data))

(define (tcbEnd)
  (printf "tcbEnd\n")
  (gl:End))

(define (errorCallback errorCode)
   (let ((estring (glu:ErrorString errorCode)))
     (printf (current-error-port) "Tessellation Error: ~A\n" estring)
     (exit 0)))

;; I assume that self-intersecting primitives would usually require a more
;; complex process than merely copying the data!?
;;
(define (tcbCombine) ;;  c d w)
  (let ((nv (list->f64vector '(0 0 0))))
    ;;  (f64vector-set! nv 0 (f64vector-ref c 0))
    ;;  (f64vector-set! nv 1 (f64vector-ref c 1))
    ;;  (f64vector-set! nv 2 (f64vector-ref c 2))
    nv))

;; Create the polygon using a tesselator
;;
(define (createTessPolygon)
  (gl:ClearColor 0.0 0.0 0.0 0.0)
  (let ((tobj (glu:NewTess)))
    (print "createTessPolygon")
    (gl:NewList startList gl:COMPILE)
    (glu:TessCallback tobj glu:TESS_BEGIN tcbBegin)
    (glu:TessCallback tobj glu:TESS_VERTEX tbbVertex)
    (glu:TessCallback tobj glu:TESS_END tcbEnd)
    (glu:TessCallback tobj glu:TESS_ERROR  errorCallback)
    (glu:TessCallback tobj glu:TESS_COMBINE tcbCombine)
    (gl:ShadeModel gl:FLAT)
    (glu:TessBeginPolygon tobj #f)
    (glu:TessBeginContour tobj)
    (glu:TessVertex tobj (f64vector 0.9 0.9 0.0) #f)
    (glu:TessVertex tobj (f64vector 0.3 0.5 0.0) #f)
    (glu:TessVertex tobj (f64vector 0.9 0.1 0.0) #f)
    (glu:TessEndContour tobj)
    (glu:TessEndPolygon tobj)
    (gl:EndList)))

(define (drawTessPolygon)
  (print "drawTessPolygon")
  (gl:Clear gl:COLOR_BUFFER_BIT)
  (gl:Color4f 1.0 1.0 1.0 0.75)
  (gl:PushMatrix)
  (gl:CallList startList)
  (gl:PopMatrix)
  (gl:Flush))

;;
;; end tesselation code (except for the call below in display)
;;

(define (display)
  (gl:Clear gl:COLOR_BUFFER_BIT)
  (if leftFirst
      (begin
        (drawTessPolygon)
        (gl:CallList 1))
      (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.

(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* 0))
(init)
(createTessPolygon)
(glut:ReshapeFunc reshape)
(glut:KeyboardFunc keyboard)
(glut:DisplayFunc display)
(glut:MainLoop)

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