From 2d6b4200cf731e17f144e86d8b52615e6e78c85b Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Sun, 1 Dec 2013 22:32:35 -0500
Subject: Update example.

---
 examples/rewrite-test.scm | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/examples/rewrite-test.scm b/examples/rewrite-test.scm
index 311e747..3582174 100644
--- a/examples/rewrite-test.scm
+++ b/examples/rewrite-test.scm
@@ -1,6 +1,7 @@
 (use-modules (srfi srfi-1)
              (2d color)
              (2d game)
+             (2d keyboard)
              (2d signals)
              (2d sprite)
              (2d texture)
@@ -11,34 +12,34 @@
 (with-window (make-window #:title "FRP is cool"
                           #:resolution (vector2 640 480)
                           #:fullscreen? #f)
-
+  ;; Move when arrow keys are pressed.
   (define move
     (make-signal
      #:init (vector2 320 240)
      #:transformer (lambda (value old from)
-                     (if (eq? from arrows)
-                         old
-                         (v+ (vscale (signal-ref arrows) 5)
-                             old)))
-     #:connectors (list arrows (time-every))))
+                     (v+ (vscale (signal-ref key-arrows) 4) old))
+     #:filter (lambda (value old from)
+                (not (eq? from key-arrows)))
+     #:connectors (list key-arrows (time-every))))
 
   (define ghost-texture (load-texture "images/ghost.png"))
 
-  (define sprite
-    (make-sprite ghost-texture
-                 #:position move))
+  (define ghost (make-sprite ghost-texture #:position move))
 
   (define follower-count 8)
+
   (define followers
     (list-tabulate
      follower-count
      (lambda (i)
        (make-sprite ghost-texture
-                    #:position (time-delay (* (- follower-count i) 1) move)
-                    #:color (make-color 1 1 1 (/ (1+ i) 16))))))
+                    ;; Follow ghost with some delay.
+                    #:position (time-delay (* (- follower-count i) 10) move)
+                    ;; Make each ghost more translucent than the last.
+                    #:color (let ((alpha (/ (1+ i)
+                                            (* 2 follower-count))))
+                              (make-color 1 1 1 alpha))))))
 
-  ;; Temporary hack. There shouldn't be side effects like this in
-  ;; signals.
   (define quit-on-esc
     (signal-lift (lambda (down?)
                    (when down?
@@ -47,6 +48,6 @@
 
   (define (draw)
     (for-each draw-sprite followers)
-    (draw-sprite sprite))
+    (draw-sprite ghost))
 
   (run-game #:draw draw))
-- 
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