wave.rkt

#lang racket

; TODO: fix this so it actually works for more functions and graph views

(require 2htdp/image)
(require 2htdp/universe)
(require test-engine/racket-tests)

(define WIDTH 200)
(define HEIGHT 200)

(define XMIN 0)
(define XMAX (* 2 pi))
(define YMIN -1)
(define YMAX 1)

(define TICK-STEP .10)

(struct graph (width height xmin xmax ymin ymax))
(struct posn (x y))

(define (posn=? p1 p2)
  (and (= (posn-x p1)
          (posn-x p2))
       (= (posn-y p1)
          (posn-y p2))))

(define GRAPH (graph WIDTH HEIGHT XMIN XMAX YMIN YMAX))

(define (value-to-coord g p)
  (posn (/ (* (posn-x p) (graph-width g)) (- (graph-xmax g) (graph-xmin g)))
        (/ (* (- (graph-ymax g) (posn-y p)) (graph-height g)) (- (graph-ymax g) (graph-ymin g)))))

(check-expect (posn=? (value-to-coord GRAPH (posn 0 1))
                      (posn 0 0))
              true)
(check-expect (posn=? (value-to-coord GRAPH (posn (/ pi 2) -1))
                      (posn 50 200))
              true)

(define (print-posn p)
  (string-append "x: " (number->string (posn-x p))
                 " "
                 "y: " (number->string (posn-y p))))

(define (draw-dot p)
  (place-image (circle 5 'solid 'red)
               (posn-x p)
               (posn-y p)
               (empty-scene WIDTH HEIGHT)))

(define (draw-scene tick)
  (let* ([step (* tick TICK-STEP)]
         [num-cycles (floor (/ step XMAX))]
         [real-step (- step (* num-cycles XMAX))]
         [x (+ XMIN real-step)]
         [y (/ (sin x) 1.5)]
         [p (value-to-coord GRAPH (posn x y))])
    (draw-dot p)))

(test)
(animate draw-scene)