HTML5 Canvas的使用

2015/08/13 38963
<!doctype html>
<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
<head>
<meta charset="gb2312">
<title> 测试</title>

<script type="text/javascript">



window.onload = function () { 
C = Math.cos; 
S = Math.sin;
U=0;
canvas = document.getElementById("myCanvas");
c = canvas.getContext("2d");

var W = canvas.width = window.innerWidth;
var H = canvas.height = window.innerHeight;

var U=180>>0;

c.fillRect(0, 0, W, H); // resize <canvas> and draw black rect (default)
c.globalCompositeOperation = "lighter"; // switch to additive color application
c.lineWidth = 10.0;//设置画笔的大小
c.lineCap = "round";//设置圆滑
t = 0;
var bool = 0;

canvas.onmousemove = function (e) {

 if(window.T) {
   if(D==0) { 
	   D=Math.random()*15;}
	   clearTimeout(T);
  }


X = e.pageX; // grab mouse pixel coords
Y = e.pageY;

R = e.pageX/W
r = e.pageY/H

a=0; // previous coord.x
b=0; // previous coord.y 
A = X, // original coord.x 
B = Y; // original coord.y 
U=e.pageX/H * 360 >>0;
D=0;	
g = Math.PI/180;

T = setInterval(f = function (e) { 
 c.save();
  c.globalCompositeOperation = "source-over";  
   if(e!=1) {
    c.fillStyle = "rgba(0,0,0,0.1)";
    c.fillRect(0, 0, W, H); 
   }
 
   c.restore();

   i = 30; 
   
   while(i --) {
 
    c.beginPath();
 
    if(D > 200 || bool) { // decrease diameter
 
     if(!bool) { // has hit maximum
 
      bool = 1;
 
     }
 
     if(D < 0.1) { // has hit minimum
 
      bool = 0;
 
     }
 
     t -= g; // decrease theta
 
     D -= 0.1; // decrease size
 
    }
 
    if(!bool) {
 
     t += g; // increase theta
 
     D += 0.1; // increase size
 
    }
	
	
	x = D*C(t)+X;
	y = D*S(t)+Y;
	

	
	if (a) { 
 
     c.moveTo(a, b);
 
     c.lineTo(x, y);
    }

	c.strokeStyle = "hsla(" + (U % 360) + ",100%,50%,0.75)"; // draw rainbow hypotrochoid
 
    c.stroke();
 
    a = x; // set previous coord.x
 
    b = y; // set previous coord.y
	
	
	U -= 0.5; // increment hue
 
   A = X; // set original coord.x
 
   B = Y; // set original coord.y
	
   }

},20);
}
}

</script>


</head>

<body style="margin:0px;padding:0px;width:100%;height:100%;overflow:hidden;">
 
<canvas id="myCanvas"></canvas>
 
</body>
</html>
代码片段
