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+;;;; examples/09-ghoulspree.lisp
+
+(defpackage #:ww.examples/9
+  (:use #:cl)
+  (:export #:start)
+  (:import-from #:defclass-std #:defclass/std))
+
+(in-package #:ww.examples/9)
+
+;;; CLASSES
+
+(defclass/std  ghoulspree (ww::application)
+  ((ghouls-per-click :std 50)))
+
+(defclass/std ghoul (ww:bitmap)
+  ((dx dy dr :std)))
+
+;;; UTILITY FUNCTIONS
+
+(defun make-ghoul (x y)
+  (make-instance 'ghoul :texture (ww:get-asset "Fezghoul.png")
+                        :x x :y y
+                        :dr (random-velocity)
+                        :dx (random-velocity 5)
+                        :dy (random-velocity 5)))
+
+(defun out-of-bounds-p (ghoul)
+  (not
+   (and
+    (< -50 (ww:x ghoul) 850)
+    (< -50 (ww:y ghoul) 650))))
+
+(defun random-velocity (&optional (size 1.0))
+  (* size (if (< 0.5 (random 1.0))
+              (random 1.0)
+              (* -1 (random 1.0)))))
+
+(defun advance-pos (thing)
+  (with-accessors ((dr dr) (dx dx) (dy dy) (x ww::x) (y ww::y) (r ww::rotation)) thing
+    (incf x dx)
+    (incf y dy)
+    (incf r dr))) ;; rotation diminishes every round, just aesthetic.
+
+(defun clamp (lo val hi)
+  "Returns VAL if (< LO VAL HI), otherwise returns LO or HI depending
+on which boundary VAL is outside of."
+  (max lo (min val hi)))
+
+(ww:defhandler moveghouls
+    (ww:on-perframe (app)
+      (loop for ghoul in (ww:container-units app)
+            do (advance-pos ghoul)
+            when (out-of-bounds-p ghoul)
+              do (ww:drop-unit ghoul))))
+
+(ww:defhandler add-ghouls
+    (ww:on-mousedown (app x y)
+      (loop repeat (ghouls-per-click app)
+            do (ww:add-unit app (make-ghoul x y)))))
+
+
+(defmethod ww::boot ((app ghoulspree))
+  "Adds the intro text and sets up the start button handler."
+  (ww:add-handler app #'add-ghouls)
+  (ww:add-handler app #'moveghouls))
+
+(defun start ()
+  (ww::start
+   (make-instance
+    'ghoulspree
+    :fps 60
+    :width 800
+    :height 600
+    :refocus-on-mousedown-p nil
+    :title "Click to add ghouls"
+    :asset-root
+    (merge-pathnames
+     "examples/"
+     (asdf:system-source-directory :wheelwork)))))