HTML5版径向渐变梯度色彩
有个读者问我如何用HTML5生成一个径向梯度色彩效果,而不使用图片。仔细思考下,其实这个问题一点都不难,请看代码。
HTML
<!DOCTYPE html> <html > <head> <meta charset="utf-8" /> <meta name="author" content="Script Tutorials" /> <title>HTML5 Radial Gradient | Script Tutorials</title> <!-- add styles --> <link href="css/main.css" rel="stylesheet" type="text/css" /> <!-- add script --> <script src="js/script.js"> </script> </head> <body> <div> <canvas id="gradient" width="500" height="500" tabindex="1"> </canvas> </div> </body> </html>
JS
// Get angle color function function getAngleColor(angle) { var color, d; if (angle < Math.PI * 2 / 5) { // angle: 0-72 d = 255 / (Math.PI * 2 / 5) * angle; color = '255,' + Math.round(d) + ',0'; // color: 255,0,0 - 255,255,0 } else if (angle < Math.PI * 4 / 5) { // angle: 72-144 d = 255 / (Math.PI * 2 / 5) * (angle - Math.PI * 2 / 5); color = (255 - Math.round(d)) + ',255,0'; // color: 255,255,0 - 0,255,0 } else if (angle < Math.PI * 6 / 5) { // angle: 144-216 d = 255 / (Math.PI * 2 / 5) * (angle - Math.PI * 4 / 5); color = '0,255,' + Math.round(d); // color: 0,255,0 - 0,255,255 } else if (angle < Math.PI * 8 / 5) { // angle: 216-288 d = 255 / (Math.PI * 2 / 5) * (angle - Math.PI * 6 / 5); color = '0,'+(255 - Math.round(d)) + ',255'; // color: 0,255,255 - 0,0,255 } else { // angle: 288-360 d = 255 / (Math.PI * 2 / 5) * (angle - Math.PI * 8 / 5); color = Math.round(d) + ',0,' + (255 - Math.round(d)) ; // color: 0,0,255 - 255,0,0 } return color; } // inner variables var iSectors = 360; var iSectorAngle = (360 / iSectors) / 180 * Math.PI; // in radians // Draw radial gradient function function drawGradient() { // prepare canvas and context objects var canvas = document.getElementById('gradient'); var ctx = canvas.getContext('2d'); // clear canvas ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height); // save current context ctx.save(); // move to center ctx.translate(canvas.width / 2, canvas.height / 2); // draw all sectors for (var i = 0; i < iSectors; i++) { // start and end angles (in radians) var startAngle = 0; var endAngle = startAngle + iSectorAngle; // radius for sectors var radius = (canvas.width / 2) - 1; // get angle color var color = getAngleColor(iSectorAngle * i); // draw a sector ctx.beginPath(); ctx.moveTo(0, 0); ctx.arc(0, 0, radius, startAngle, endAngle, false); ctx.closePath(); // stroke a sector ctx.strokeStyle = 'rgb('+color+')'; ctx.stroke(); // fill a sector ctx.fillStyle = 'rgb('+color+')'; ctx.fill(); // rotate to the next sector ctx.rotate(iSectorAngle); } // restore context ctx.restore(); } // initialization if(window.attachEvent) { window.attachEvent('onload', drawGradient); } else { if(window.onload) { var curronload = window.onload; var newonload = function() { curronload(); drawGradient(); }; window.onload = newonload; } else { window.onload = drawGradient; } }
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HTML5 is a key technology for building modern web pages, providing many new elements and features. 1. HTML5 introduces semantic elements such as, , etc., which enhances web page structure and SEO. 2. Support multimedia elements and embed media without plug-ins. 3. Forms enhance new input types and verification properties, simplifying the verification process. 4. Offer offline and local storage functions to improve web page performance and user experience.

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H5 is not just the abbreviation of HTML5, it represents a wider modern web development technology ecosystem: 1. H5 includes HTML5, CSS3, JavaScript and related APIs and technologies; 2. It provides a richer, interactive and smooth user experience, and can run seamlessly on multiple devices; 3. Using the H5 technology stack, you can create responsive web pages and complex interactive functions.

H5 and HTML5 refer to the same thing, namely HTML5. HTML5 is the fifth version of HTML, bringing new features such as semantic tags, multimedia support, canvas and graphics, offline storage and local storage, improving the expressiveness and interactivity of web pages.

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