前端的代码：

function drawArrow(angle)
{
	//Init canvas
	var canvas = $('#cv_Arrow')[0];
	var context = canvas.getContext('2d');
	var width = canvas.width;
	var height = canvas.height;
	context.clearRect(0, 0, width, height);

	//Rotate
	var distance = iconSize / 2 * Math.sqrt(2) * Math.sin(angle * Math.PI / 180 / 2) * 2;
	var degree = 180 - 45 - (180 - angle) / 2;
	var x = distance * Math.sin(degree * Math.PI / 180);
	var y = distance * Math.cos(degree * Math.PI / 180);
	context.translate(x, -y);
	var angleInRadians = angle * Math.PI / 180;
	context.rotate(angleInRadians);

	//Draw arrow
	context.fillStyle = 'rgb(0,0,0)'; //Black
	context.lineWidth = 1;
	context.strokeStyle = "#000000"; //Black
	context.lineCap = 'round'; //Circle angle
	context.lineJoin = 'round';
	context.beginPath();
	context.moveTo(iconSize / 2, border);
	context.lineTo(border, iconSize - border);
	context.lineTo(iconSize / 2, iconSize / 2);
	context.fill();
	context.stroke();
	context.closePath();
	context.save();

	context.restore();
	context.fillStyle = 'rgb(255,255,255)'; //White
	context.lineWidth = 1;
	context.strokeStyle = "#000000";
	context.lineCap = 'round';
	context.lineJoin = 'round';
	context.beginPath();
	context.moveTo(iconSize / 2, border);
	context.lineTo(iconSize - border, iconSize - border);
	context.lineTo(iconSize / 2, iconSize / 2);
	context.fill();
	context.stroke();
	context.closePath();
	context.save();

	_canvas = canvas;
}

发送到后台的代码：

for (var i = 0; i < 360; i++)
{
	drawArrow(1);

	var data = _canvas.toDataURL();

	//删除字符串前的提示信息 "data:image/png;base64,"
	var b64 = data.substring(22);

	$.ajax({ url: "RotateCanvas.aspx", data: { data: b64, name: i.toString() }, success:
			function ()
			{
		 	//alert('OK');
			}
	});
}

后台接收的代码：

if (Request["name"] != null)
{
	string name = Request["name"];
	String savePath = Server.MapPath("~/images/output/");

	try
	{
		FileStream fs = File.Create(savePath + "/" + name + ".png");
		byte[] bytes = Convert.FromBase64String(Request["data"]);

		fs.Write(bytes, 0, bytes.Length);
		fs.Close();
	}
	catch (Exception ex)
	{
	}
}

最后生成的结果：

生成图片的效果很棒，不失真，而且透明的，不需要后期处理。