DECLARE SUB Render3DBox (x!, y!, wd!, ht!, vpx!, vpy!, c1!, c2!, dp!)
DECLARE SUB Sleep1 (n!)
SCREEN 12

Render3DBox 100, 100, 40, 40, x, y, 15, 1, 20
Render3DBox 100, 100, 40, 40, x, y, 0, 0, 20

SUB Render3DBox (x, y, wd, ht, vpx, vpy, c1, c2, dp)
LINE (x, y)-(x + wd, y + ht), c1, B
IF (vpx < x) OR (vpy < y) THEN LINE (x, y)-(vpx, vpy), c1                      '   upper left
IF (vpx > x + wd) OR (vpy < y) THEN LINE (x + wd, y)-(vpx, vpy), c1            '   lower left
IF (vpx < x) OR (vpy > y + ht) THEN LINE (x, y + ht)-(vpx, vpy), c1           '   upper right
IF (vpx > x + wd) OR (vpy > y + ht) THEN LINE (x + wd, y + ht)-(vpx, vpy), c1  '   lower right
LINE (x + 1, y + 1)-(x + wd - 1, y + ht - 1), c2, BF
END SUB

SUB Sleep1 (n)
a = TIMER + n
DO UNTIL TIMER >= a: LOOP
END SUB