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