examples/ex-26.rkt
#lang racket
(require (planet wcy/mpost-wrapper))
(provide main)
(define (main)
  (let ((A (point '-1.5cm '-1.5cm))
        (B (point '1.5cm '-1.5cm))
        (C (point '1.5cm '1.5cm))
        (D (point '-1.5cm '1.5cm)))
    (fill (op-- A C B D  'cycle) #:withcolor (op* 0.8 'white))
    (draw (op-- (point '-1.5cm 0) (point '1.5cm '0)))
    (draw (op-- (point 0 '-1.5cm) (point 0 '1.5cm)))
    (drawarrow (op-- (point 0 0) (point '1cm 0))
               #:withpen (scale '2bp 'pencircle))
    (drawarrow (op-- (point 0 0) (point 0 '1cm))
               #:withpen (scale '2bp 'pencircle))))