[comp.lang.scheme] PC Scheme 3.03, %GRAPHICS-primitive no. 4

hahnt@kiss.informatik.tu-muenchen.de.informatik.tu-muenchen.dbp.de (07/11/90)

The following procedure shows that pixelvalues with a vertical position
greater than 255 are not gettable, although they are settable in video-modes
15, 16 and 18. 

(define *vm* 18) ;16 15

(define (test)
  (set-video-mode! *vm*)
  (do ((i 0 (1+ i)))
      ((begin (%graphics 1 0 i 15 0 0 0) 
              (<> 15 (%graphics 4 0 i 0 0 0 0)))
       (set-video-mode! 3) i)))