Hi,
I thought I'd try a simple GUI app using the world/universe mutation-free
approach, but trying to implement the 'world/universe' program design
myself.
I've got my little sketch below, but I quickly came to conclusion that
while I could use the teachpack, I don't know how to achieve the teachpack
functionality myself.
I'm guessing I should use continuations, but that doesn't seem to be the
approach in the universe.rkt source.
I could always just stuff the program into the canvas class, (as earlier
games like slidey and same seem to do), but I really want to get a handle
on how to implement the 'world/universe' style of program control.
Any suggestons would be appreciated.
Kind regards,
Stephen
;;;;----
#lang racket/gui
; simple drawing program
; mousedown starts recording a list of points
; mousechanged starts recording a new list
; paint callback paints the list of lists as lines.
(define diagramframe (new frame% [label "paint"] [width 300] [height 300]
[x 1000][y 300]))
;(define lines '(((0 . 0) (0 . 300) (250 . 250) (150 . 176))))
(define lines '(((0 . 0) (0 . 300) (250 . 250) (150 . 176))
((10 . 4) (280 . 10))))
(define paintcanvas%
(class canvas%
(init-field mouse-event-callback)
(super-new)
(define dc (send this get-dc))
(define/override (on-event mouse-event)
(mouse-event-callback mouse-event))))
(define (paint-cb c dc)
(for-each (λ (line) (send dc draw-lines line)) lines))
(define (me-cb mouse-event)
(let ((x (send mouse-event get-x))
(y (send mouse-event get-y)))
(when (and (send mouse-event get-left-down)
(send mouse-event moving?))
(if (send mouse-event button-changed?)
; if true append as new list
'()
; if false append existing list
'())))
)
(define Paintcanvas (new paintcanvas%
[parent diagramframe]
[paint-callback paint-cb]
[mouse-event-callback me-cb]))
(define (main world)
(when world (main (??? world)))
(send diagramframe show #t))
(main lines)
(send diagramframe show #t)
;;-----
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