//生成并渲染出验证码图形
function draw(show_num) {
	var canvas_width=$('#canvas').width();
	var canvas_height=$('#canvas').height();
	var canvas = document.getElementById("canvas");//获取到canvas的对象，演员
	var context = canvas.getContext("2d");//获取到canvas画图的环境，演员表演的舞台
	canvas.width = canvas_width;
	canvas.height = canvas_height;
	var sCode = "a,b,c,d,e,f,g,h,i,j,k,m,n,p,q,r,s,t,u,v,w,x,y,z,A,B,C,E,F,G,H,J,K,L,M,N,P,Q,R,S,T,W,X,Y,Z,1,2,3,4,5,6,7,8,9,0";
	var aCode = sCode.split(",");
	var aLength = aCode.length;//获取到数组的长度
	for (var i = 0; i < 6; i++) {  //这里的for循环可以控制验证码位数（如果想显示6位数，4改成6即可）
		var j = Math.floor(Math.random() * aLength);//获取到随机的索引值
		// var deg = Math.random() * 30 * Math.PI / 180;//产生0~30之间的随机弧度
		var deg = Math.random() - 0.5; //产生一个随机弧度
		var txt = aCode[j];//得到随机的一个内容
		show_num[i] = txt.toLowerCase();
		var x = 15 + i * 20;//文字在canvas上的x坐标
		var y = 30 + Math.random() * 8;//文字在canvas上的y坐标
		context.font = "bold 30px 微软雅黑";
		context.translate(x, y);
		context.rotate(deg);
		context.fillStyle = randomColor();
		context.fillText(txt, 0, 0);
		context.rotate(-deg);
		context.translate(-x, -y);
	}
	for (var i = 0; i <= 5; i++) { //验证码上显示线条
		context.strokeStyle = randomColor();
		context.beginPath();
		context.moveTo(Math.random() * canvas_width, Math.random() * canvas_height);
		context.lineTo(Math.random() * canvas_width, Math.random() * canvas_height);
		context.stroke();
	}
	for (var i = 0; i <= 30; i++) { //验证码上显示小点
		context.strokeStyle = randomColor();
		context.beginPath();
		var x = Math.random() * canvas_width;
		var y = Math.random() * canvas_height;
		context.moveTo(x, y);
		context.lineTo(x + 1, y + 1);
		context.stroke();
	}
}
//得到随机的颜色值
function randomColor() {
	var r = Math.floor(Math.random() * 256);
	var g = Math.floor(Math.random() * 256);
	var b = Math.floor(Math.random() * 256);
	return "rgb(" + r + "," + g + "," + b + ")";
}