"use strict"; var page = require('webpage').create(); page.viewportSize = { width: 400, height : 400 }; page.content = '

'; page.evaluate(function() { var el = document.getElementById('surface'), context = el.getContext('2d'), width = window.innerWidth, height = window.innerHeight, cx = width / 2, cy = height / 2, radius = width / 2.3, imageData, pixels, hue, sat, value, i = 0, x, y, rx, ry, d, f, g, p, u, v, w, rgb; el.width = width; el.height = height; imageData = context.createImageData(width, height); pixels = imageData.data; for (y = 0; y < height; y = y + 1) { for (x = 0; x < width; x = x + 1, i = i + 4) { rx = x - cx; ry = y - cy; d = rx * rx + ry * ry; if (d < radius * radius) { hue = 6 * (Math.atan2(ry, rx) + Math.PI) / (2 * Math.PI); sat = Math.sqrt(d) / radius; g = Math.floor(hue); f = hue - g; u = 255 * (1 - sat); v = 255 * (1 - sat * f); w = 255 * (1 - sat * (1 - f)); pixels[i] = [255, v, u, u, w, 255, 255][g]; pixels[i + 1] = [w, 255, 255, v, u, u, w][g]; pixels[i + 2] = [u, u, w, 255, 255, v, u][g]; pixels[i + 3] = 255; } } } context.putImageData(imageData, 0, 0); document.body.style.backgroundColor = 'white'; document.body.style.margin = '0px'; }); page.render('colorwheel.png'); phantom.exit();