Instructions: 1. Stare at the background and you will see a green dot rotating. 2. Follow the green dot and it will disappear. 3. Focus on the '+' in the middle and after a while the pink dots will disappear 4. Stare at the top circle and more weird stuff happens. Adapted from: http://visualfunhouse.com/animations/disappearing-dots-illusion.html

gistfile1.lisp

(ql:quickload :lispbuilder-sdl)
(in-package :lispbuilder-sdl)


(defparameter *radius* 50 "The radius of the button in Pixels.")
(defparameter *active-color* (sdl:color :r 178 :g 178 :b 178))
(defparameter *inactive-color* *magenta*)
(defvar *active* 0 "The index of the 'active' circle.")

(defparameter *positions* (list (point :x 300 :y 100) ; Top
                                (point :x 441.42136 :y 158.57864)   ; Top-Right
                                (point :x 500 :y 300) ; Right
                                (point :x 441.42136 :y 441.42136) ; Bottom-Right
                                (point :x 300 :y 500) ; Bottom
                                (point :x 158.57864 :y 441.42136) ; Bottom-Left
                                (point :x 100 :y 300) ;; Left
                                (point :x 158.57864 :y 158.57864)) ; Top-Left
  "List of points where the radius go. 200 distance from the center at
 (300,300) ")

(sdl:with-init ()
  (sdl:window 600 600 :bpp 24 :sw t)
  (setf (frame-rate) 10)
  (sdl:with-events ()
    (:quit-event () t)
    (:idle ()
           (draw-box-* 0 0 600 600 :color *active-color*)
           (loop
             :for center :in *positions*
             :for index :from 0
             :do (draw-filled-circle center *radius*
                                     :color (if (eql index *active*)
                                                *active-color*
                                                *inactive-color*)))
           

           (draw-line (point :x 290 :y 300)
                      (point :x 310 :y 300)
                      :color *black*)
           (draw-line (point :x 300 :y 290)
                      (point :x 300 :y 310)
                      :color *black*)

           (setf *active* (if (< (1+ *active*) (length *positions*))
                              (1+ *active*)
                              0))
           (sdl:update-display))))