点在线的方位判断

private function getDirection(point:Point, startPoint:Point, endPoint:Point):String
{
	//根据数学,求出直接的表达示:y=kx+b   
	var direction:String;

	var g:Number;

	if (startPoint.x != endPoint.x )
	{
		var k:Number=(startPoint.y - endPoint.y) / (startPoint.x - endPoint.x);
		var b:Number=startPoint.y - k * startPoint.x;
		g = point.y - k*point.x - b;

		if(k>0){
			if(g<=0){
				direction = "right_top";
			}else if(g>0){
				direction = "left_bottom";
			}
		}else if(k<0){
			if(g<=0){
				direction = "left_top";
			}else if(g>0){
				direction = "right_bottom";
			}
		}else{
			if(g<=0){
				direction = "top";
			}else if(g>0){
				direction = "bottom";
			}
		}

	}
	else
	{
		g = point.x - startPoint.x;
		if(g>=0){
			direction = "right";
		}else if(g<0){
			direction = "left";
		}
	}
	return direction;
}