► |  | How to Design Programs Teachpacks

1 | Ht DP Teachpacks
2 | Ht DP/ 2e Teachpacks

▼ | 1 | Ht DP Teachpacks

1.1 | Manipulating Images: "image.ss"
1.2 | Simulations and Animations: "world.ss"
1.3 | Converting Temperatures: "convert.ss"
1.4 | Guessing Numbers: "guess.ss"
1.5 | Master Minding: "master.ss"
1.6 | Playing Master Mind: "master-play.ss"
1.7 | Simple Drawing: "draw.ss"
1.8 | Hangman: "hangman.ss"
1.9 | Playing Hangman: "hangman-play.ss"
1.10 | Managing Control Arrows: "arrow.ss"
1.11 | Manipulating Simple HTML Documents: "docs.ss"
1.12 | Working with Files and Directories: "dir.ss"
1.13 | Graphing Functions: "graphing.ss"
1.14 | Simple Graphical User Interfaces: "gui.ss"
1.15 | An Arrow GUI: "arrow-gui.ss"
1.16 | Controlling an Elevator: "elevator.ss"
1.17 | Lookup GUI: "lkup-gui.ss"
1.18 | Guess GUI: "guess-gui.ss"
1.19 | Queens: "show-queen.ss"
1.20 | Matrix Functions: "matrix.ss"

On this page:

control-left-right
control-up-down
control

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#### 1.10`` Managing Control Arrows: "arrow.ss"

( require htdp/arrow )

The teachpack implements a controller for moving shapes across a canvass.

> > procedure

> > ( control-left-right shape n move draw) → true

> shape : Shape
> n : number?
> move : ( -> number? Shape Shape)
> draw : ( -> Shape true )

Moves shape n pixels left (negative) or right (positive).

> > procedure

> > ( control-up-down shape n move draw) → true

> shape : Shape
> n : number?
> move : ( -> number? Shape Shape)
> draw : ( -> Shape true )

Moves shape n pixels up (negative) or down (positive).

> > procedure

> > ( control shape n move-lr move-ud draw) → true

> shape : Shape
> n : number?
> move-lr : ( -> number? Shape Shape)
> move-ud : ( -> number? Shape Shape)
> draw : ( -> Shape true )

Moves shape N pixels left or right and up or down, respectively.

Example:

> ; A shape is a structure:
> ; (make-posn num num)
> ; RAD : the radius of the simple disk moving across a canvas
> ( define RAD 10)
> ; move : number shape -> shape or false
> ; to move a shape by delta according to translate
> ; effect: to redraw it
> ( define (move delta sh)
> ( cond
> [( and (clear-solid-disk sh RAD)
> (draw-solid-disk (translate sh delta) RAD))
> (translate sh delta)]
> [ else false ]))
> ; translate : shape number -> shape
> ; to translate a shape by delta in the x direction
> ( define (translate sh delta)
> (make-posn ( + (posn-x sh) delta) (posn-y sh)))
> ; draw-it : shape -> true
> ; to draw a shape on the canvas: a disk with radius
> ( define (draw-it sh)
> (draw-solid-disk sh RAD))
> ; Run:
> ; this creates the canvas
> (start 100 50)
> ; this creates the controller GUI
> ( control-left-right (make-posn 10 20) 10 move draw-it)

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