8 A More Complicated Example

The use of multiple viewports, viewport descriptors, drawing operations for multiple viewports is as easy as the use of a single viewport:

  (open-graphics)
  (let* (; w1 and w2 are viewports for different windows
         [w1  (open-viewport "viewport 1" 300 300)]
         [w2  (open-viewport "viewport 2" 200 500)]
         ; d1 and d2 draw lines in different viewports
         [d1  (draw-line w1)]
         [d2  (draw-line w2)])
    ; draws a line in viewport labeled viewport 1
    (d1 (make-posn 100 5) (make-posn 5 100))
    ; draws a line in viewport labeled viewport 2
    (d2 (make-posn 100 100) (make-posn 101 400)))
  
  ; we no longer have access to viewports 1 and 2,
  ; since their descriptors did not escape the let
  (close-graphics)
  ; removes the viewports