Bug in pushwin() on 4D/20

[Joe Ilacqua]

	There is a bug in pushwin() such that if there is any time between
when the window is pushed and the next time you draw, no draws will work.

	This happens on our 4D/20s running '4D-3.1 4D/20 REV. B'.  On
our 4D/70 running '4D-3.1 REV. C' this bug does not appear.  Will this
be fixed in REV. C for the 4D/20 or does this bug only occur on the
4D/20.

	The following code demonstrates the bug in hopes of making
this clearer.

Joe Ilacqua
Associative Design Technology

-- cut here --
#include <gl.h>

  Coord points [][2] = {500,300, 300,700, 700,700};
    
main() {  
  prefposition(0,XMAXSCREEN,0,YMAXSCREEN);
  foreground();
  noborder();  /* Games without frontiers... */
  winopen("");
  
  color(WHITE);
  clear();       /* Clear screen to white */
  
  color(GREEN);  /* Draw a green triangle */
  polf2(3,points);  

#define TEST1

#ifdef TEST1
  winpush();   /* All three shapes draw in this test */
  sleep (10);
#endif

/* #define TEST2 */

#ifdef TEST2 
  sleep (10); /* only the polygon draws in this test */
  winpush();
#endif

/* #define TEST3 */

#ifdef TEST3
  winpush(); /* All three shapes draw in this test */
#endif

  color(RED);
  rectfi(400,400,600,600);
  color(BLUE);
  circfi(500,500,50);
  sleep(30);
}