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An optical illusion in ClojureScript & big-bang, ported from http://djfav.com/2014/01/24/illusory-cones/ - originally written in javascript by Jon Faviell.
(ns big-bang.examples.illusory-cones
(:require
[big-bang.core :refer [big-bang]]
[jayq.core :refer [show]]
[enchilada :refer [ctx canvas canvas-size]]
[monet.canvas :refer [clear-rect circle fill-style fill
save restore translate rotate]]))
(def initial-state
(let [[width height] (canvas-size)]
{ :t 0
:radius 200
:canvas {:x 0 :y 0 :w width :h height}
:mid-point [(/ width 2) (/ height 2)]}))
(defn update-state [event world-state]
(update-in world-state [:t] (partial + 0.5)))
(defn draw-circles [ctx num-circles radius]
(doseq [i (range 1 num-circles)
:let [color (if (odd? i) :black :white)]]
(->
ctx
(fill-style color)
(circle {:x (* (Math/sin (/ i 2)) num-circles)
:y 0
:r (- radius (* i (/ num-circles 2)))})))
ctx)
(defn render [{:keys [t radius canvas mid-point] :as world-state}]
(->
ctx
(clear-rect canvas)
(save)
(translate (first mid-point) (second mid-point))
(rotate (/ t Math/PI))
(draw-circles 20 radius)
(restore)))
(show canvas)
(big-bang
:initial-state initial-state
:on-tick update-state
:tick-rate 50
:to-draw render)
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