olimex-buffer.rkt

(define white #b111111111111)
(define blue  #b111100000000)
(define green #b000011110000)
(define red   #b000000001111)


;Tile smaller than 10 might slow drawing, but will not cause flashes
(define tile 10) ;size of a `pixel'
(define size 13) ;number of pixels (/ 130 10)
(define index 169) ;total number of pixels
(define buffer (make-vector index white)) ;the pixel buffer


(define (get-ref x y) ;buffer index of point with x y
  (+ (* y size) x))

(define (get-x ref) ;x position for buffer index
  (modulo ref size))

(define (get-y ref) ;y position for buffer index
  (floor (/ ref size)))


(define (set-px! x y color) ;set color of point in buffer
  (let ((ref (get-ref (int x) (int y))))
    (vector-set! buffer ref color)))

(define (int num) (inexact->exact (floor num))) ;convert float to valid vector index

(define (each proc!)
  (let iter ((ctr 0)
             (res #f))
    (if (= ctr index)
      res
      (iter
        (+ ctr 1)
        (proc! ctr)))))

(define (draw!) ;draw the buffer to screen
  (each
    (lambda (ref)
      (fill-rectangle!
        (* (get-x ref) tile)
        (* (get-y ref) tile)
        tile tile
        (vector-ref buffer ref)))))

(define (clear!) ;clear the buffer (white)
  (each
    (lambda (ref)
      (vector-set! buffer ref white))))



;Test Code

(define pos (cons 3 3)) ;position of test object
(define spd 0.3) ;movement speed of test object

(define (start)
  (let iter ()
    (let ((x (car pos))
          (y (cdr pos)))

      (begin ;; Render
        (clear!)
        (set-px! x y blue)
        (draw!))

      (begin ;; Update
        (set-car! pos (+ x spd))
        (cond ;keeps test object on the screen
          ((< x 2)  (set! spd (+ (abs spd))))   ;move right
          ((> x 11) (set! spd (- (abs spd)))))) ;move left

      (iter))))


(start) ;start the `game loop'