BMAP* white_map = "white.pcx"; // a solid white 64x64 image
PANEL* white_pan ={
   alpha = 0;
   bmap  = white_map;
   flags = TRANSLUCENT;
}
void _fade_white_inandout(){
   if (is(white_pan, SHOW)) return;
   set (white_pan, SHOW);
   white_pan.alpha = 0;
   white_pan.scale_x = screen_size.x;
   white_pan.scale_y = screen_size.y;
   while (white_pan.alpha < 100){
      white_pan.alpha += time_step * 2;
      wait (1);
   }
   while (white_pan.alpha > 0){
      white_pan.alpha -= time_step * 2;
      wait (1);
   }   
   reset (white_pan, SHOW);
}