#bg

$colors: (
  #fff,
  #fff,
  #fff,
  #fff,
  #fff,
  #666667,
  #fff,
  #F7F7F7,
  #fff,
#fff,
);
$color: nth($colors, random(length($colors)));

html {
  background: radial-gradient(ellipse at center, $color 0%, darken($color, 20%) 70%);
  overflow: hidden;
} 

var refreshDuration = 10000;
var refreshTimeout;
var numPointsX;
var numPointsY;
var unitWidth;
var unitHeight;
var points;

function onLoad()
{
    var svg = document.createElementNS('https://www.w3.org/2000/svg', 'svg');
    svg.setAttribute('width',window.innerWidth);
    svg.setAttribute('height',window.innerHeight);
    document.querySelector('#bg').appendChild(svg);

    var unitSize = (window.innerWidth+window.innerHeight)/20;
    numPointsX = Math.ceil(window.innerWidth/unitSize)+1;
    numPointsY = Math.ceil(window.innerHeight/unitSize)+1;
    unitWidth = Math.ceil(window.innerWidth/(numPointsX-1));
    unitHeight = Math.ceil(window.innerHeight/(numPointsY-1));

    points = [];

    for(var y = 0; y < numPointsY; y++) {
        for(var x = 0; x < numPointsX; x++) {
            points.push({x:unitWidth*x, y:unitHeight*y, originX:unitWidth*x, originY:unitHeight*y});
        }
    }

    randomize();

    for(var i = 0; i < points.length; i++) {
        if(points[i].originX != unitWidth*(numPointsX-1) && points[i].originY != unitHeight*(numPointsY-1)) {
            var topLeftX = points[i].x;
            var topLeftY = points[i].y;
            var topRightX = points[i+1].x;
            var topRightY = points[i+1].y;
            var bottomLeftX = points[i+numPointsX].x;
            var bottomLeftY = points[i+numPointsX].y;
            var bottomRightX = points[i+numPointsX+1].x;
            var bottomRightY = points[i+numPointsX+1].y;

            var rando = Math.floor(Math.random()*2);

            for(var n = 0; n < 2; n++) {
                var polygon = document.createElementNS(svg.namespaceURI, 'polygon');

                if(rando==0) {
                    if(n==0) {
                        polygon.point1 = i;
                        polygon.point2 = i+numPointsX;
                        polygon.point3 = i+numPointsX+1;
                        polygon.setAttribute('points',topLeftX+','+topLeftY+' '+bottomLeftX+','+bottomLeftY+' '+bottomRightX+','+bottomRightY);
                    } else if(n==1) {
                        polygon.point1 = i;
                        polygon.point2 = i+1;
                        polygon.point3 = i+numPointsX+1;
                        polygon.setAttribute('points',topLeftX+','+topLeftY+' '+topRightX+','+topRightY+' '+bottomRightX+','+bottomRightY);
                    }
                } else if(rando==1) {
                    if(n==0) {
                        polygon.point1 = i;
                        polygon.point2 = i+numPointsX;
                        polygon.point3 = i+1;
                        polygon.setAttribute('points',topLeftX+','+topLeftY+' '+bottomLeftX+','+bottomLeftY+' '+topRightX+','+topRightY);
                    } else if(n==1) {
                        polygon.point1 = i+numPointsX;
                        polygon.point2 = i+1;
                        polygon.point3 = i+numPointsX+1;
                        polygon.setAttribute('points',bottomLeftX+','+bottomLeftY+' '+topRightX+','+topRightY+' '+bottomRightX+','+bottomRightY);
                    }
                }
                polygon.setAttribute('fill','rgba(0,0,0,'+(Math.random()/3)+')');
                var animate = document.createElementNS('https://www.w3.org/2000/svg','animate');
                animate.setAttribute('fill','freeze');
                animate.setAttribute('attributeName','points');
                animate.setAttribute('dur',refreshDuration+'ms');
                animate.setAttribute('calcMode','linear');
                polygon.appendChild(animate);
                svg.appendChild(polygon);
            }
        }
    }

    refresh();

}

function randomize() {
    for(var i = 0; i < points.length; i++) {
        if(points[i].originX != 0 && points[i].originX != unitWidth*(numPointsX-1)) {
            points[i].x = points[i].originX + Math.random()*unitWidth-unitWidth/2;
        }
        if(points[i].originY != 0 && points[i].originY != unitHeight*(numPointsY-1)) {
            points[i].y = points[i].originY + Math.random()*unitHeight-unitHeight/2;
        }
    }
}

function refresh() {
    randomize();
    for(var i = 0; i < document.querySelector('#bg svg').childNodes.length; i++) {
        var polygon = document.querySelector('#bg svg').childNodes[i];
        var animate = polygon.childNodes[0];
        if(animate.getAttribute('to')) {
            animate.setAttribute('from',animate.getAttribute('to'));
        }
        animate.setAttribute('to',points[polygon.point1].x+','+points[polygon.point1].y+' '+points[polygon.point2].x+','+points[polygon.point2].y+' '+points[polygon.point3].x+','+points[polygon.point3].y);
        animate.beginElement();
    }
    refreshTimeout = setTimeout(function() {refresh();}, refreshDuration);
}

function onResize() {
    document.querySelector('#bg svg').remove();
    clearTimeout(refreshTimeout);
    onLoad();
}

window.onload = onLoad;
window.onresize = onResize;