net: Add snake.rkt.

* net/ricketyspace/ror/six/resources/body.gif: New file.
* net/ricketyspace/ror/six/resources/goo.gif: New file.
* net/ricketyspace/ror/six/resources/head.gif: New file.
* net/ricketyspace/ror/six/resources/tail.gif: New file.
* net/ricketyspace/ror/six/snake.rkt: New file.

5 files changed, 216 insertions, 0 deletions

diff --git a/net/ricketyspace/ror/six/resources/body.gif b/net/ricketyspace/ror/six/resources/body.gif
new file mode 100644
index 0000000..94a0956
--- /dev/null
+++ b/net/ricketyspace/ror/six/resources/body.gif
diff --git a/net/ricketyspace/ror/six/resources/goo.gif b/net/ricketyspace/ror/six/resources/goo.gif
new file mode 100644
index 0000000..cb0d98b
--- /dev/null
+++ b/net/ricketyspace/ror/six/resources/goo.gif
diff --git a/net/ricketyspace/ror/six/resources/head.gif b/net/ricketyspace/ror/six/resources/head.gif
new file mode 100644
index 0000000..664f679
--- /dev/null
+++ b/net/ricketyspace/ror/six/resources/head.gif
diff --git a/net/ricketyspace/ror/six/resources/tail.gif b/net/ricketyspace/ror/six/resources/tail.gif
new file mode 100644
index 0000000..6fbd317
--- /dev/null
+++ b/net/ricketyspace/ror/six/resources/tail.gif
diff --git a/net/ricketyspace/ror/six/snake.rkt b/net/ricketyspace/ror/six/snake.rkt
new file mode 100644
index 0000000..90d40d3
--- /dev/null
+++ b/net/ricketyspace/ror/six/snake.rkt
@@ -0,0 +1,216 @@
+#lang racket
+(require 2htdp/universe 2htdp/image)
+
+;; data
+(struct pit (snake goos))
+(struct snake (dir segs))
+(struct goo (loc expire))
+(struct posn (x y))
+
+;; constants
+(define TICK-RATE 1/10)
+
+(define SIZE 30)
+
+(define SEG-SIZE 15)
+
+(define EXPIRATION-TIME 150)
+
+(define WIDTH-PX (* SEG-SIZE 30))
+(define HEIGHT-PX (* SEG-SIZE 30))
+
+(define MT-SCENE (empty-scene WIDTH-PX HEIGHT-PX))
+(define GOO-IMG (bitmap "resources/goo.gif"))
+(define SEG-IMG (bitmap "resources/body.gif"))
+(define HEAD-IMG (bitmap "resources/head.gif"))
+
+(define HEAD-LEFT-IMG HEAD-IMG)
+(define HEAD-DOWN-IMG (rotate 90 HEAD-LEFT-IMG))
+(define HEAD-RIGHT-IMG (flip-horizontal HEAD-LEFT-IMG))
+(define HEAD-UP-IMG (flip-vertical HEAD-DOWN-IMG))
+
+(define ENDGAME-TEXT-SIZE 15)
+
+;; main
+(define (start-snake)
+  (big-bang (pit (snake "right" (list (posn 1 1)))
+                 (list (fresh-goo)
+                       (fresh-goo)
+                       (fresh-goo)
+                       (fresh-goo)
+                       (fresh-goo)
+                       (fresh-goo)))
+            (on-tick next-pit TICK-RATE)
+            (on-key direct-snake)
+            (to-draw render-pit)
+            (stop-when dead? render-end)))
+
+(define (next-pit w)
+  (define snake (pit-snake w))
+  (define goos (pit-goos w))
+  (define goo-to-eat (can-eat snake goos))
+  (if goo-to-eat
+      (pit (grow snake) (age-goo (eat goos goo-to-eat)))
+      (pit (slither snake) (age-goo goos))))
+
+(define (direct-snake w ke)
+  (cond [(dir? ke) (world-change-dir w ke)]
+        [else w]))
+
+(define (render-pit w)
+  (snake+scene (pit-snake w)
+               (goo-list+scene (pit-goos w) MT-SCENE)))
+
+(define (dead? w)
+  (define snake (pit-snake w))
+  (or (self-colliding? snake) (wall-colliding? snake)))
+
+(define (render-end w)
+  (overlay (text "Game Over" ENDGAME-TEXT-SIZE "black")
+           (render-pit w)))
+
+
+;; clock
+(define (can-eat snake goos)
+  (cond [(empty? goos) #f]
+        [else (if (close? (snake-head snake) (first goos))
+                  (first goos)
+                  (can-eat snake (rest goos)))]))
+
+(define (eat goos goo-to-eat)
+  (cons (fresh-goo) (remove goo-to-eat goos)))
+
+(define (close? s g)
+  (posn=? s (goo-loc g)))
+
+(define (grow sn)
+  (snake (snake-dir sn)
+         (cons (next-head sn) (snake-segs sn))))
+
+(define (slither sn)
+  (snake (snake-dir sn)
+         (cons (next-head sn) (all-but-last (snake-segs sn)))))
+
+(define (next-head sn)
+  (define head (snake-head sn))
+  (define dir (snake-dir sn))
+  (cond [(string=? dir "up") (posn-move head 0 -1)]
+        [(string=? dir "down") (posn-move head 0 1)]
+        [(string=? dir "left") (posn-move head -1 0)]
+        [(string=? dir "right") (posn-move head 1 0)]))
+
+(define (posn-move p dx dy)
+  (posn (+ (posn-x p) dx)
+        (+ (posn-y p) dy)))
+
+(define (all-but-last segs)
+  (cond [(empty? (rest segs)) empty]
+        [else (cons (first segs) (all-but-last (rest segs)))]))
+
+(define (age-goo goos)
+  (rot (renew goos)))
+
+(define (renew goos)
+  (cond [(empty? goos) empty]
+        [(rotten? (first goos))
+         (cons (fresh-goo) (renew (rest goos)))]
+        [else
+         (cons (first goos) (renew (rest goos)))]))
+
+(define (rot goos)
+  (cond [(empty? goos) empty]
+        [else (cons (decay (first goos)) (rot (rest goos)))]))
+
+(define (rotten? g)
+  (zero? (goo-expire g)))
+
+(define (decay g)
+  (goo (goo-loc g) (sub1 (goo-expire g))))
+
+(define (fresh-goo)
+  (goo (posn (add1 (random (sub1 SIZE)))
+             (add1 (random (sub1 SIZE))))
+       EXPIRATION-TIME))
+
+
+;; keys
+(define (dir? x)
+  (or (key=? x "up")
+      (key=? x "down")
+      (key=? x "left")
+      (key=? x "right")))
+
+(define (world-change-dir w d)
+  (define the-snake (pit-snake w))
+  (cond [(and (opposite-dir? (snake-dir the-snake) d)
+              (cons? (rest (snake-segs the-snake))))
+         (stop-with w)]
+        [else
+         (pit (snake-change-dir the-snake d) (pit-goos w))]))
+
+(define (opposite-dir? d1 d2)
+  (cond [(string=? d1 "up") (string=? d2 "down")]
+        [(string=? d1 "down") (string=? d2 "up")]
+        [(string=? d1 "left") (string=? d2 "right")]
+        [(string=? d1 "right") (string=? d2 "left")]))
+
+
+;; render
+(define (snake+scene snake scene)
+  (define snake-body-scene
+    (img-list+scene (snake-body snake) SEG-IMG scene))
+  (define dir (snake-dir snake))
+  (img+scene (snake-head snake)
+             (cond [(string=? "up" dir) HEAD-UP-IMG]
+                   [(string=? "down" dir) HEAD-DOWN-IMG]
+                   [(string=? "left" dir) HEAD-LEFT-IMG]
+                   [(string=? "right" dir) HEAD-RIGHT-IMG])
+             snake-body-scene))
+
+(define (goo-list+scene goos scene)
+  (define (get-posns-from-goo goos)
+    (cond [(empty? goos) empty]
+          [else (cons (goo-loc (first goos))
+                      (get-posns-from-goo (rest goos)))]))
+  (img-list+scene (get-posns-from-goo goos) GOO-IMG scene))
+
+(define (img-list+scene posns img scene)
+  (cond [(empty? posns) scene]
+        [else (img+scene
+               (first posns)
+               img
+               (img-list+scene (rest posns) img scene))]))
+
+(define (img+scene posn img scene)
+  (place-image img
+               (* (posn-x posn) SEG-SIZE)
+               (* (posn-y posn) SEG-SIZE)
+               scene))
+
+
+;; end game
+(define (self-colliding? snake)
+  (cons? (member (snake-head snake) (snake-body snake))))
+
+(define (wall-colliding? snake)
+  (define x (posn-x (snake-head snake)))
+  (define y (posn-y (snake-head snake)))
+  (or (= 0 x) (= x SIZE)
+      (= 0 y) (= y SIZE)))
+
+;; aux
+(define (posn=? p1 p2)
+  (and (= (posn-x p1) (posn-x p2))
+       (= (posn-y p1) (posn-y p2))))
+
+(define (snake-head sn)
+  (first (snake-segs sn)))
+
+(define (snake-body sn)
+  (rest (snake-segs sn)))
+
+(define (snake-tail sn)
+  (last (snake-segs sn)))
+
+(define (snake-change-dir sn d)
+  (snake d (snake-segs sn)))