arrow.ss
A shape is a class of data for which move
and
draw
operations can be drawn.
The teachpack arrow.ss
implements controller for moving
shapes across a canvass. It provides three operations:
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))
;; TESTS:
;; this creates the canvas
(start 100 50)
;; this creates the controller GUI
(control-left-right (make-posn 10 20) 10 move draw-it)