bug#21359: 24.5; [PATCH] Fix apple spawning behaviour

bug#21359: 24.5; [PATCH] Fix apple spawning behaviour

[Vasilij Schneidermann]

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Classic renditions of Snake initially place an apple at a random
position, then spawn it anew if and only if it has been eaten by the
snake.  M-x snake behaves differently, it does spawn apples in regular
time intervals at former positions of the snake's tail.  To put it
bluntly, this makes it look as if the snake is leaking apples.

The attached patch introduces a new function, `snake-set-dot` which is
called at game initialization and upon collision with an apple.  The
code responsible for placing apples in periodic intervals got snipped
out, together with the now unnecessary `snake-cycle` variable
responsible for tracking at which position the apple emission cycle is.



In GNU Emacs 24.5.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.16.2)
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diff --git a/lisp/play/snake.el b/lisp/play/snake.el
index d42ba44..c1e7e9f 100644
--- a/lisp/play/snake.el
+++ b/lisp/play/snake.el
@@ -144,7 +144,6 @@
 (defvar snake-velocity-x 1)
 (defvar snake-velocity-y 0)
 (defvar snake-positions nil)
-(defvar snake-cycle 0)
 (defvar snake-score 0)
 (defvar snake-paused nil)
 (defvar snake-moved-p nil)
@@ -164,7 +163,6 @@ and then start moving it leftwards.")
 (make-variable-buffer-local 'snake-velocity-x)
 (make-variable-buffer-local 'snake-velocity-y)
 (make-variable-buffer-local 'snake-positions)
-(make-variable-buffer-local 'snake-cycle)
 (make-variable-buffer-local 'snake-score)
 (make-variable-buffer-local 'snake-paused)
 (make-variable-buffer-local 'snake-moved-p)
@@ -237,7 +235,6 @@ and then start moving it leftwards.")
 	snake-velocity-x	snake-initial-velocity-x
 	snake-velocity-y	snake-initial-velocity-y
 	snake-positions		nil
-	snake-cycle		1
 	snake-score		0
 	snake-paused		nil
 	snake-moved-p           nil
@@ -251,6 +248,14 @@ and then start moving it leftwards.")
       (cl-incf y snake-velocity-y)))
   (snake-update-score))
 
+(defun snake-set-dot ()
+  (let ((x (random snake-width))
+	(y (random snake-height)))
+    (while (not (= (gamegrid-get-cell x y) snake-blank))
+      (setq x (random snake-width))
+      (setq y (random snake-height)))
+    (gamegrid-set-cell x y snake-dot)))
+
 (defun snake-update-game (snake-buffer)
   "Called on each clock tick.
 Advances the snake one square, testing for collision.
@@ -268,23 +273,20 @@ Argument SNAKE-BUFFER is the name of the buffer."
 	(cond ((= c snake-dot)
 	       (cl-incf snake-length)
 	       (cl-incf snake-score)
-	       (snake-update-score))
+	       (snake-update-score)
+	       (snake-set-dot))
 	      (t
 	       (let* ((last-cons (nthcdr (- snake-length 2)
 					 snake-positions))
 		      (tail-pos (cadr last-cons))
 		      (x0 (aref tail-pos 0))
 		      (y0 (aref tail-pos 1)))
-		 (gamegrid-set-cell x0 y0
-				    (if (= (% snake-cycle 5) 0)
-					snake-dot
-				      snake-blank))
-		 (cl-incf snake-cycle)
+		 (gamegrid-set-cell x0 y0 snake-blank)
 		 (setcdr last-cons nil))))
 	(gamegrid-set-cell x y snake-snake)
 	(setq snake-positions
 	      (cons (vector x y) snake-positions))
-	  (setq snake-moved-p nil)))))
+	(setq snake-moved-p nil)))))
 
 (defun snake-update-velocity ()
   (unless snake-moved-p
@@ -339,6 +341,7 @@ Argument SNAKE-BUFFER is the name of the buffer."
   "Start a new game of Snake."
   (interactive)
   (snake-reset-game)
+  (snake-set-dot)
   (use-local-map snake-mode-map)
   (gamegrid-start-timer snake-tick-period 'snake-update-game))

bug#21359: 24.5; [PATCH] Fix apple spawning behaviour

[Vasilij Schneidermann]

I was made aware of <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=6749>
which covers roughly the same ground, but didn't make it through because
the author forgot about following up.

bug#21359: 24.5; [PATCH] Fix apple spawning behaviour

[Lars Ingebrigtsen]

Vasilij Schneidermann <v.schneidermann@gmail.com> writes:

> I was made aware of <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=6749>
> which covers roughly the same ground, but didn't make it through because
> the author forgot about following up.

I've now closed that report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#21359: 24.5; [PATCH] Fix apple spawning behaviour

[Lars Ingebrigtsen]

Vasilij Schneidermann <v.schneidermann@gmail.com> writes:

> The attached patch introduces a new function, `snake-set-dot` which is
> called at game initialization and upon collision with an apple. The
> code responsible for placing apples in periodic intervals got snipped
> out, together with the now unnecessary `snake-cycle` variable
> responsible for tracking at which position the apple emission cycle is.

Looks good; applying to the Emacs trunk.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no