详解HTML5 Canvas绘制时指定颜色与透明度的方法

</style> </head>

<canvas id="canvas"> 你的浏览器居然不支持Canvas？！赶快换一个吧！！

</canvas> </div>

window.onload = function(){ var canvas = document.getElementById("canvas");

canvas.width = 800; canvas.height = 600;

var context = canvas.getContext("2d"); context.fillStyle = "#FFF";

context.fillRect(0,0,800,600);

context.globalAlpha = 0.5;

for(var i=0; i<=50; i++){ var R = Math.floor(Math.random() * 255);

var G = Math.floor(Math.random() * 255); var B = Math.floor(Math.random() * 255);

context.fillStyle = "rgb(" + R + "," + G + "," + B + ")";

context.beginPath();

context.arc(Math.random() * canvas.width, Math.random() * canvas.height, Math.random() * 100, 0, Math.PI * 2); context.fill();

} };