;; The first three lines of this file were inserted by DrScheme. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-advanced-reader.ss" "lang")((modname |animation slowdown|) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #t #t none #f ())))
(require 2htdp/image)
(require 2htdp/universe)

; INSERT HI-RES IMAGE HERE ********
;; I used a 1200x900 cut-n-paste of a digicam photo via MS Paint 
(define HI-RES {text "Insert large bitmap here" 20 "black"})

(define SIZE 800)

;; The WorldState is a (make-world Posn List-of-Posn}
(define-struct world (ball bricks))
(define init-world (make-world (make-posn 100 200)
                               (build-list 3000 (lambda (n) (make-posn (random SIZE) (random SIZE))))))

(define BACKGROUND (rectangle SIZE SIZE "solid" "white"))
(define BRICK (rectangle 5 2 "solid" "blue"))
(define BALL (circle 5 "solid" "red"))
(define speed 5)

;; place-brick : Posn Image -> Image
;; Adds a brick image at the given point into the given image
(define (place-brick pos background)
  (place-image BRICK (posn-x pos) (posn-y pos) background))

;; An image constant containing all the brick images overlaid on the blank background
(define BRICKS (foldr place-brick BACKGROUND (world-bricks init-world)))

;; Tick-handler simply moves the ball in a world-wrapping straight line
(define (tick-handler ws)
  (local [(define (move-ball pos) (make-posn (modulo (+ speed (posn-x pos)) SIZE) (modulo (+ speed (posn-y pos)) SIZE)))]
    (make-world (move-ball (world-ball ws))
                (world-bricks ws))))

;; Render draws the ball and one version of the background
(define (render ws)
  (place-image BALL (posn-x (world-ball ws)) (posn-y (world-ball ws))
               
               ;;; Four ways to draw the ball's background.  Uncomment one at a time.
               
               ;; 1. Blank background to see the ball move at full speed
               BACKGROUND
               
               ;; 2. Use place-image to build a new background image depending on current state
               ;(foldr place-brick BACKGROUND (world-bricks ws))
               
               ;; 3. Use a constant image, full of rectangles, as the background
               ;BRICKS                  
               
               ;; 4. Use a constant high-resolution "flat?" image for the background
               ;(place-image HI-RES (/ SIZE 2) (/ SIZE 2) BACKGROUND)
               )
  )

(big-bang init-world (on-tick tick-handler) (on-draw render))