73 lines
1.9 KiB
Racket
73 lines
1.9 KiB
Racket
#lang scribble/doc
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@(require scribble/manual "shared.rkt"
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(for-label scheme teachpack/htdp/arrow))
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@teachpack["arrow"]{Managing Control Arrows}
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@;declare-exporting[teachpack/htdp/arrow]
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@defmodule[#:require-form beginner-require htdp/arrow]
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The teachpack implements a controller for moving shapes across a canvass.
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@defproc[(control-left-right
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[shape Shape]
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[n number?]
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[move (-> number? Shape Shape)]
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[draw (-> Shape true)]) true]{Moves shape @racket[n] pixels left
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(negative) or right (positive).}
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@defproc[(control-up-down
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[shape Shape]
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[n number?]
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[move (-> number? Shape Shape)]
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[draw (-> Shape true)]) true]{Moves shape @racket[n] pixels up
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(negative) or down (positive).}
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@defproc[(control
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[shape Shape]
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[n number?]
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[move-lr (-> number? Shape Shape)]
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[move-ud (-> number? Shape Shape)]
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[draw (-> Shape true)]) true]{
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Moves shape @racket[N] pixels left or right and up or down, respectively.}
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Example:
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@(begin
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#reader scribble/comment-reader
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(racketblock
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;; A shape is a structure:
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;; (make-posn num num)
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;; RAD : the radius of the simple disk moving across a canvas
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(define RAD 10)
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;; move : number shape -> shape or false
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;; to move a shape by delta according to translate
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;; effect: to redraw it
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(define (move delta sh)
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(cond
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[(and (clear-solid-disk sh RAD)
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(draw-solid-disk (translate sh delta) RAD))
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(translate sh delta)]
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[else false]))
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;; translate : shape number -> shape
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;; to translate a shape by delta in the x direction
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(define (translate sh delta)
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(make-posn (+ (posn-x sh) delta) (posn-y sh)))
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;; draw-it : shape -> true
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;; to draw a shape on the canvas: a disk with radius
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(define (draw-it sh)
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(draw-solid-disk sh RAD))
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;; Run:
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;; this creates the canvas
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(start 100 50)
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;; this creates the controller GUI
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(control-left-right (make-posn 10 20) 10 move draw-it)
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))
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