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function avg(a,b,n){ return (a*(n-1) + b)/n }
function rand(n){ return Math.random()*n }
function randint(n) { return ~~(Math.random()*n) }
function randrange(a,b){ return a+rand(b-a) }
function choice(a) { return a[randint(a.length)] }
function clamp(n,a,b) { return a > n ? a : n > b ? b : n }
function sign(n){ return n < 0 ? -1 : 1 }
function mod(n,m){ return n-(m * Math.floor(n/m)) }
function lerp(n,a,b){ return (b-a)*n+a }
function quantize(m,n){ return n * ((m/n)|0) }
function randgauss (obj, jog) {
var radius = Math.random() * jog
var angle = Math.random() * Math.PI * 2
obj.left += Math.sin(angle) * radius
obj.top += Math.cos(angle) * radius
}
function shuffle(a){
for (var i = a.length; i > 0; i--){
var r = randint(i)
var swap = a[i-1]
a[i-1] = a[r]
a[r] = swap
}
return a
}
function toArray (els){
return Array.prototype.slice.apply(els)
}
// easing functions
function circular (t) { return Math.sqrt( 1 - ( --t * t ) ) }
function quadratic (t) { return t * ( 2 - t ) }
function back (t) {
var b = 4;
return ( t = t - 1 ) * t * ( ( b + 1 ) * t + b ) + 1;
}
function bounce (t) {
if (t >= 1) return 1;
if ( ( t /= 1 ) < ( 1 / 2.75 ) ) {
return 7.5625 * t * t;
} else if ( t < ( 2 / 2.75 ) ) {
return 7.5625 * ( t -= ( 1.5 / 2.75 ) ) * t + 0.75;
} else if ( t < ( 2.5 / 2.75 ) ) {
return 7.5625 * ( t -= ( 2.25 / 2.75 ) ) * t + 0.9375;
} else {
return 7.5625 * ( t -= ( 2.625 / 2.75 ) ) * t + 0.984375;
}
}
function elastic (t) {
var f = 0.22,
e = 0.4;
if ( t === 0 ) { return 0; }
if ( t == 1 ) { return 1; }
return ( e * Math.pow( 2, - 10 * t ) * Math.sin( ( t - f / 4 ) * ( 2 * Math.PI ) / f ) + 1 );
}
function preload (url) {
var img = new Image ()
var loaded = false, _cb
img.onload = function(){
if (loaded) return
loaded = true
if (_cb) { _cb(img) }
}
img.src = url
if (img.complete) { img.onload() }
return {
then: function(cb){
if (loaded) { cb(img) }
else { _cb = cb }
}
}
}
function preloadImages () {
var images = toArray(document.getElementById("images").children)
var count = 0, ready = false, _cb
images.forEach(function(img){
var loaded = false
img.onload = function(){
if (loaded) return
loaded = true
done(img)
}
if (img.complete) { img.onload() }
})
function done () {
if (++count == images.length && ! ready) {
ready = true
_cb && _cb()
}
}
return {
then: function(cb){
if (ready) { cb() }
else { _cb = cb }
}
}
}
function smoothstep(min,max,n){
var t = clamp((n - min) / (max - min), 0.0, 1.0);
return t * t * (3.0 - 2.0 * t)
}
function detrand (x,y) {
return (Math.sin( x * 12.9898 + y * 78.233 ) * 43758.5453) % 1
}
function gray_to_transparency(img) {
var canvas = document.createElement("canvas")
var ctx = canvas.getContext('2d')
var nw = img.naturalWidth, nh = img.naturalHeight
canvas.width = nw
canvas.height = nh
ctx.drawImage(img,0,0)
var pixels = ctx.getImageData(0,0,nw,nh)
var data = pixels.data
for (var i = 0, len = nw*nh*4; i < len; i += 4) {
data[i+3] = data[i]
data[i] = data[i+1] = data[i+2] = 255
}
ctx.putImageData(pixels,0,0)
return canvas
}
var TWO_PI = 2*Math.PI
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