#lang racket
(require 2htdp/image 2htdp/universe)
; main : CarState -> CarState
; launch the program from some initial state
(define (main r)
(big-bang 0 (on-tick tock r) (to-draw render)))
(define wheel-radius 5)
(define cab
(beside (rectangle (* 6 wheel-radius)(* 4 wheel-radius) "solid" "red")
(right-triangle (* 2 wheel-radius) (* 4 wheel-radius) "solid" "red")))
(define body
(rectangle (* 20 wheel-radius) (* 6 wheel-radius) "solid" "red"))
(define top
(above/align "right" cab body))
(define tire
(circle wheel-radius "solid" "black"))
(define bot
(beside tire
(rectangle (* 5 wheel-radius) (* 2 wheel-radius) "solid" "white")
tire))
(define auto
(above top bot))
(define WIDTH 1000)
(define SPEED (* 0.54 (image-width auto)))
(define Y-CAR 50)
(define BACKGROUND (empty-scene WIDTH 200))
; CarState -> CarState
; the clock ticked; move the car by three pixels
; example:
; given: 20, expected 23
; given: 78, expected 81
(define (tock ws)
(modulo (+ ws SPEED) WIDTH)
#;
(if (< ws (-(image-width BACKGROUND) (* 0.54 (image-width auto))))
(+ ws 3)
( - ws (image-width BACKGROUND))))
; PositiveNumber -> Image
; run the animation at the specified rate [1/28 is decent, try 1/100 too]
(define (render ws)
(place-image auto ws Y-CAR BACKGROUND))
On Mar 12, 2012, at 10:24 AM, ROELOF WOBBEN wrote:
> Hello,
>
> I have tried to make a function which display a car running on a empty-screen.
> When the car is at the end. The car has to begin at the beginning.
>
> I have made this :
>
> (define wheel-radius 5)
> (define cab (beside (rectangle (* 6 wheel-radius)(* 4 wheel-radius) "solid"
> "red")(right-triangle (* 2 wheel-radius) (* 4 wheel-radius) "solid" "red")))
> (define body (rectangle (* 20 wheel-radius) (* 6 wheel-radius) "solid" "red"))
> (define top (above/align "right" cab body))
> (define tire (circle wheel-radius "solid" "black"))
> (define bot (beside tire (rectangle (* 5 wheel-radius) (* 2 wheel-radius)
> "solid" "white") tire))
> (define auto (above top bot))
>
> (define Y-CAR 50)
> (define BACKGROUND (empty-scene 1000 200))
>
> ; CarState -> CarState
> ; the clock ticked; move the car by three pixels
> ; example:
> ; given: 20, expected 23
> ; given: 78, expected 81
> (define (tock ws)
> (if (< ws (-(image-width BACKGROUND)(* 0.54 (image-width auto))))(+ ws 3)
> ( - ws (image-width BACKGROUND))))
>
> ; CarState -> Image
> ; place the car into a scene, according to the given world state
> (define (render ws)
> (place-image auto ws Y-CAR BACKGROUND))
>
> ; main : CarState -> CarState
> ; launch the program from some initial state
> (define (main ws)
> (big-bang ws (on-tick tock) (to-draw render)))
>
> But now I wonder if I can do the same with setting the variable ws to zero.
> So like this : If ws is smaller then the image-width increase with the half
> width of the car. then ws = ws+ 3 else ws = 0
>
> Regards,
>
> Roelof
>
>
>
>
>
>
>
>
>
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