求复杂多边形面积的算法

struct Point
{
    float x, y;
};

//Get the area of a complex polygon(refer from skeinforge)
float getAreaLoop(vector<Point> loop)
{
	float areaLoopDouble=0;
	
	Point point,pointEnd;
	
	int i,length=loop.size();
	
	for(i=0;i!=length;++i)
	{
		point=loop[i];
		
		pointEnd=loop[(i + 1) % length];
		
		areaLoopDouble += point.x * pointEnd.y - pointEnd.x * point.y;
	}
	
	return 0.5 * areaLoopDouble;
}