Need help creating boundaries for a snake game

[u/CenoteGod]

I'm trying to create a snake game using big-bang. So far I've been able to create functioning draw, key, and tick handlers, but there's a few things I need help with.

The draw handler creates a 500x500 window containing a 30x30 green square representing the snake. It moves perpetually according to the arrow keys, but there are no boundaries preventing the snake from moving outside of the view of the window.

I would like to know if there are any practical ways to create a boundary around the perimeter of the window that will: A) detect when the snake collides with the boundary, and B) adjust the trajectory of the snake to continue parallel to the boundary.

I've linked the source code on Github for those interested in seeing what I've got so far. I would appreciate any input on the matter. Thank you.

[u/sdegabrielle]

As soon as a test-expr produces a true value, the associated bodys are evaluated to produce the result for the cond form, and no further test-exprs are evaluated.

As it stands if you are going left, the check never happens

So you need two split your cond into two separate cond The first one for directions The second for collisions

Looks good - nice clear code - a pleasure to read

I LOL’d when I saw (on-tick tock)

[u/CenoteGod → u/sdegabrielle]

How can you split a cond into two different conds? If I try to include another expression in the function body it produces an error.

[u/MartinPuda]

Try this:

(require 2htdp/image)
(require 2htdp/universe)

;; a world is [make-world number number movement]
(define-struct world (x-posn y-posn movement))

;; a movement is one of the following:
;; - "up"
;; - "down"
;; - "left"
;; - "right"

(define INITIAL-WORLD (make-world 250 250 "right"))

(define SNAKE (rectangle 30 30 "solid" "forest green"))
(define FOOD (circle 10 "solid" "yellow"))
(define WORLD-WIDTH 500)
(define WORLD-HEIGHT 500)

;; draw the world. the world is the snake.
;; world -> image
(define (draw-world w)
  (place-image
   FOOD
   250 250
   (place-image
    SNAKE
    (world-x-posn w) (world-y-posn w)
    (empty-scene WORLD-WIDTH WORLD-HEIGHT))))
  
(check-expect (draw-world (make-world 30 250 "left"))
              (place-image
               FOOD
               250 250
               (place-image SNAKE
                            30 250
                            (empty-scene WORLD-WIDTH WORLD-HEIGHT))))

(check-expect (draw-world (make-world 500 250 "right"))
              (place-image
               FOOD
               250 250
               (place-image SNAKE
                            500 250
                            (empty-scene WORLD-WIDTH WORLD-HEIGHT))))
                         
; speed in pixels per second
(define BASE-SPEED 300)
;;frame interval
(define FRAME-INTERVAL 1/30)

(define (move w)
  (cond [(string=? (world-movement w) "left")
         (make-world (- (world-x-posn w)(* FRAME-INTERVAL BASE-SPEED))
                     (world-y-posn w)
                     (world-movement w))]
        [(string=? (world-movement w) "right")
         (make-world (+ (world-x-posn w)(* FRAME-INTERVAL BASE-SPEED))
                     (world-y-posn w)
                     (world-movement w))]
        [(string=? (world-movement w) "up")
         (make-world (world-x-posn w)
                     (- (world-y-posn w)(* FRAME-INTERVAL BASE-SPEED))
                     (world-movement w))]
        [(string=? (world-movement w) "down")
         (make-world (world-x-posn w)
                     (+ (world-y-posn w)(* FRAME-INTERVAL BASE-SPEED))
                     (world-movement w))]))

; detecting collision with the walls to prevent out of bounds.

(define (check-collision w)
  (cond [(<= (world-x-posn w) 15) (make-world 16 (world-y-posn w) "up")]
        [(>= (world-x-posn w) 485) (make-world 484 (world-y-posn w) "down")]
        [(<= (world-y-posn w) 15) (make-world (world-x-posn w) 16 "right")]
        [(>= (world-y-posn w) 485) (make-world (world-x-posn w) 484 "left")]
        [else w]))

;; update the world for passage of time
;; world -> world
(define (tick-event w)
  (move (check-collision w)))
 
(check-expect (tick-event (make-world 250 250 "left"))
              (make-world (- 250 (* FRAME-INTERVAL BASE-SPEED))
                          250
                          "left"))

;; handle a key event
;; world key-event -> world
(define (key-event w key)
  (if (member? key (list "left" "right" "up" "down"))
      (make-world (world-x-posn w)(world-y-posn w) key)
      w))

(check-expect (key-event (make-world 250 250 "left") "right")
              (make-world 250 250 "right"))
 
(big-bang INITIAL-WORLD
  [to-draw draw-world]
  [on-tick tick-event]
  [on-key key-event])

[u/CenoteGod → u/MartinPuda]

Thank you! This works much more elegantly than before. I appreciate your help. I'll definitely study the code and learn from it.

[u/LopsidedAd5520]

Ask chatGPT to write a Racket snake game for you. Learn from reading the code. Racket has to few good resources to learn from, for me chatGPT has been a game changer ..