JS1k: The JavaScript code golfing competition

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// ==ClosureCompiler==
// @language_out ECMASCRIPT_2017
// @compilation_level ADVANCED_OPTIMIZATIONS
// @js_externs var w = {};
// @js_externs var d = {};
// @js_externs var a = {};
// @js_externs var c = {};
// ==/ClosureCompiler==

//var rand = max => ~~(Math.random() * max);
function rand(max) { return ~~(Math.random() * max) }
window['rand'] = rand;

var d=document;
var i;
var j;
var k;
var lerp = (x, y, t) => x * (1 - t) + y * t;
var seq = (length, func) => [...Array(length).keys()].map(func);
var canvasSize = 500;
var halfCanvasSize = 250;
var shipGridSize = 5;
var maxRadius = 9;
var animate;

onmouseup = () => {
    var ctx = seq(2, () => {
        i = d.createElement('canvas');
        i.width = i.height = canvasSize;
        j = i.getContext('2d');
        j.fillRect(0, 0, canvasSize, canvasSize);
        return j;
    });
    var [cDepth, cColor] = ctx;

    var allShapes = [[[halfCanvasSize, halfCanvasSize]]];

    var baseColor = seq(3, () => 50 + rand(150));
    var colors = seq(5, () => `rgb(${baseColor.map(color => color - 50 + rand(100)).join(',')})`);

    seq(3 + rand(7), partIndex => {
        var p = allShapes.flat();
        var [x, y] = p[rand(p.length)];
        var vertexCount = 3 + rand(5);
        var radii = seq(vertexCount * (2 - (rand(100) < 50)), () => 1.5 + rand(maxRadius));
        radii = [...radii, ...radii.reverse()];
        var shapes = seq(2, f => seq(vertexCount * 2, n => [
            (f ? canvasSize - x : x) + ~~(Math.cos((n / (vertexCount * 2 - 1) - .25) * Math.PI * 2) * radii[n]) * (1 - f * 2) * shipGridSize,
            y + ~~(Math.sin((n / (vertexCount * 2 - 1) - .25) * Math.PI * 2) * radii[n]) * shipGridSize, f ? canvasSize - x : x, y]));
        allShapes = [...allShapes, ...shapes];
        var smoothness = Math.random() + .1;
        var color = colors[rand(colors.length)];
        ctx.map((c, isColor) => shapes.map(shape => seq(25, o => {
            var inset = 1 - (1 - o / 25) ** smoothness;
            shape.map((v, n) => c[n ? 'lineTo' : 'moveTo'](lerp(v[0], v[2], inset), lerp(v[1], v[3], inset)));
            c.fillStyle = isColor ? color : `rgb(${16 + o * (1 + partIndex)},0,0)`;
            c.globalAlpha = .5;
            c.fill();
            c.beginPath();
        })));
        shapes.map(shape => shape.map((v, n) => cDepth[n ? 'lineTo' : 'moveTo'](v[0], v[1])));
        cDepth.stroke();
    });

    animate = () => {
        c.translate(halfCanvasSize, halfCanvasSize);
        halfCanvasSize *= -1;
        c.rotate(0.01);
        c.translate(halfCanvasSize, halfCanvasSize);
        halfCanvasSize *= -1;
        c.drawImage(cDepth.canvas, 0, 0);
        c.globalCompositeOperation = 'multiply';

        var id = c.getImageData(0, 0, canvasSize, canvasSize);
        l = id.data;
        for (n = 0; n < 1e+6; n++) {
            k = n % 4;
            if (!k) {
                j = i;
                i = l[n];
            }
            l[n] = k == 3 ? i * 255 : 128 + (i - j) * 15;
        }
        c.putImageData(id, 0, 0);
        c.drawImage(cColor.canvas, 0, 0);
        c.globalCompositeOperation = 'source-over';
    };
};
onmouseup();
setInterval(() => animate(), 20);