运行效果截图如下：
index.html：
<!DOCTYPE html> <html> <head> <meta http-equiv="Content-type" content="text/html;charset=UTF-8" /> <title>canvas中的透明度</title> <style type="text/css"> #canvas { background:black; margin-top:100px; margin-left:200px; } </style> </head> <body> <canvas ></canvas> </body> <script type="text/javascript" src="https://www.jb51.net/canvas.js"></script> <script type="text/javascript"> cache = {}; var offsetX = 50, offsetY = 20; cache.context = dyl.createContext('canvas'); for(var i=0; i<10; i++) { for(var j=0; j<10; j++) { var alpha = j * 0.1 + 0.1; (function(i, j ,alpha) { setTimeout(function() { dyl.rect(dyl.createColor(), i*50, j*50, 100, 100, alpha); }, 100*j*i); })(i, j ,alpha); } } </script> </html>
canvas.js：
(function() { var dyl = {cache: {}}; dyl.setContext = function(context) { dyl.cache._context = context; return context; }; dyl.getDom = function(id) { return document.getElementById(id); }; dyl._getContext = function() { return dyl.cache._context; }; dyl.save = function() { var context = dyl._getContext(); context ? context.save() : void(0); }; dyl.restore = function() { var context = dyl._getContext(); context ? context.restore() : void(0); }; dyl.createContext = function(canvasID) { var canvas = this.getDom(canvasID); if(!canvas) { return null; } return dyl.setContext(canvas.getContext("2d")); }; dyl.createColor = function() { var color = "rgb("; color += Math.round(Math.random()*255); color += ","; color += Math.round(Math.random()*255); color += ","; color += Math.round(Math.random()*255); color += ")"; return color; }; dyl.addImg = function(img, x, y) { var context = dyl._getContext(); if(!img || !context) { return; } if(typeof img === "string") { var oImg = new Image(); oImg.src = img; oImg.onload = function() { context.drawImage(oImg, x, y); } return; } context.drawImage(img, x, y); }; dyl.rect = function(color, x, y, width, height, alpha) { var context = dyl._getContext(); if(!context) { return; } context.save(); context.fillStyle = color; context.globalAlpha = alpha ? alpha : 1; context.fillRect(x, y, width, height); context.restore(); }; dyl.circle = function(color, x, y, r, alpha) { var context = dyl._getContext(); context.save(); context.fillStyle = color; context.beginPath(); context.globalAlpha = alpha ? alpha : 1; context.arc(x, y, r, 0, 2*Math.PI); context.fill(); context.stroke(); }; dyl.clearRect = function(x, y, width, height) { var context = dyl._getContext(); if(!context) { return; } context.clearRect(x, y, width, height); }; dyl.scale = function(x, y) { var context = dyl._getContext(); if(!context) { return; } x = x ? x : 1; y = y ? y : 1; context.scale(x, y); }; if(!window.dyl) { window.dyl = dyl; } })();
更多关于js特效相关内容感兴趣的读者可查看本站专题：《jQuery动画与特效用法总结》、《jQuery常见经典特效汇总》及《JavaScript动画特效与技巧汇总》