//风向，风速，原点半径，风杆长度，forsurf不用理会
function calcWindLines(wd, wf, p0, core_radius, shaftLength, forSurf) {
		var lines=[],wfmax=forSurf? 40:60;
		if(!wf || wd==null) // wf==0 || wf==null || wd==null
			return lines;
		var radius=core_radius!=null? core_radius:0;
		var slen=shaftLength!=null? shaftLength:20;
		var p1=calculateTerminalPoint(p0,radius,wd);
		var p=calculateTerminalPoint(p1,slen,wd);
		// shaft
		lines.push([p1.x,p1.y,p.x,p.y]);
		// feathers
 		var v = (wf>=0)? Math.round(wf):-1;
		var dn;
		var d=wd;
		if (v < 0) {// create a cross at p
			dn = calculateTerminalPoint(p, slen/6, d+45);
			lines.push([p.x,p.y,dn.x,dn.y]);
			dn = calculateTerminalPoint(p, slen/6, d+135);
			lines.push([p.x,p.y,dn.x,dn.y]);
			dn = calculateTerminalPoint(p, slen/6, d+225);
			lines.push([p.x,p.y,dn.x,dn.y]);
			dn = calculateTerminalPoint(p, slen/6, d+315);
			lines.push([p.x,p.y,dn.x,dn.y]);
			return lines;
		}else if (v == 1){// do nothing
			return lines;
		}else if (v == 2) {// draw a short line
			p = calculateTerminalPoint(p, slen/4, d+180);
			dn = calculateTerminalPoint(p, slen/4,d+60);
			lines.push([p.x,p.y,dn.x,dn.y]);
			return lines;
		}else if (v > wfmax) {// draw a '>' on the right of the shaft
			var p1 = calculateTerminalPoint(p, slen/5, d+180);//沿风杆向圆心移一些位置
			dn = calculateTerminalPoint(p1, slen/5, d+225);
			lines.push([p1.x,p1.y,dn.x,dn.y]);
			dn = calculateTerminalPoint(p1, slen/5, d+315);
			lines.push([p1.x,p1.y,dn.x,dn.y]);
			v = wfmax;
		}
		while(v - 20 >= 0 || v == 19){// draw triangles when necessarily
			dn = calculateTerminalPoint(p, slen*0.433, d+90);
			lines.push([p.x,p.y,dn.x,dn.y]);
			p = calculateTerminalPoint(p, slen/5, d+180);
			lines.push([p.x,p.y,dn.x,dn.y]);
			v -= 20;
			if (v < 19)
				p = calculateTerminalPoint(p, slen/7, d+180);
		}
		while(v - 4 >= 0 || v == 3){// draw long lines when necessarily
			var span=forSurf? slen/6:slen/10;
			dn = calculateTerminalPoint(p, slen/2, d+60);
			lines.push([p.x,p.y,dn.x,dn.y]);
			p = calculateTerminalPoint(p, span, d+180);
			v -= 4;
		}
		if(v > 0){// draw a short line when necessarily
			dn = calculateTerminalPoint(p, slen/4, d+60.0);
			lines.push([p.x,p.y,dn.x,dn.y]);
		}
		return lines;
};

	// 计算线段另一个端点(直角)坐标
	// @param p0 给定已知的一个端点{x,y}
	// @param length  给定长度
	// @param angle 给定角度(以正北起,0~360)
	// @return {x,y}
	function calculateTerminalPoint(p0, length, angle) {
		var a = angle * Math.PI / 180, x = length * Math.sin(a), y = length * Math.cos(a);
		return { x: p0.x + x, y: p0.y - y };
	};


    //console.log(calcWindLines(52, 1.7, p(100, 100), Math.PI * 2, 20));