20170523Canvas基础知识

html中
//画布
<canvas id="canvas"></canvas>
js中
var canvas = document.getElementById('canvas');
1、canvas的属性和方法：
canvas.width = document.documentElement.clientWidth || document.body.clientWidth;
canvas.height = document.documentElement.clientWidth || document.body.clientWidth;
//绘图上下文
var context = canvas.getContext('2d');
2、context的属性和方法
context.lineWidth = 10;
context.strokeStyle="rgb(0,255,0)";
context.fillStyle="red";
context.stroke();
context.fill();
context.arc(0,0,8,0,2*Math.PI,true);
context.clearRect(0,0,context.canvas.width,context.canvas,height);