HTML5版径向渐变梯度色彩
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2022-03-19 13:49:01
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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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