/// <summary>
/// 判断点与直线的关系，假设你站在a点朝向b点，
/// 则输入点与直线的关系分为：Left, Right or Centered on the line
/// </summary>
/// <param name="point">判断点</param>
/// <returns>判断结果</returns>
public PointSide ClassifyPoint(Vector2 point)
{
if (point == this.m_cStartPoint || point == this.m_cEndPoint)
{
return(PointSide.ON_LINE);
}
//向量a
Vector2 vectorA = this.m_cEndPoint - this.m_cStartPoint;
//向量b
Vector2 vectorB = point - this.m_cStartPoint;
float crossResult = NMath.CrossProduct(vectorA, vectorB);
if (NMath.IsEqualZero(crossResult))
{
return(PointSide.ON_LINE);
}
else if (crossResult < 0)
{
return(PointSide.RIGHT_SIDE);
}
else
{
return(PointSide.LEFT_SIDE);
}
}
/// <summary>
/// 判断是否是顺时针
/// </summary>
/// <returns></returns>
public bool IsCW()
{
if (this.m_lstPoints.Count <= 2)
{
return(false);
}
//最上（y最小）最左（x最小）点， 肯定是一个凸点
//寻找最上点
Vector2 topPoint = this.m_lstPoints[0];
int topIndex = 0;
for (int i = 1; i < this.m_lstPoints.Count; i++)
{
Vector2 currPoint = this.m_lstPoints[i];
if ((topPoint.y > currPoint.y) ||
((topPoint.y == currPoint.y) && (topPoint.x > currPoint.x)))
{
topPoint = currPoint;
topIndex = i;
}
}
//寻找左右邻居
int preIndex = (topIndex - 1) >= 0 ? (topIndex - 1) : (this.m_lstPoints.Count - 1);
int nextIndex = (topIndex + 1) < this.m_lstPoints.Count ? (topIndex + 1) : 0;
Vector2 prePoint = this.m_lstPoints[preIndex];
Vector2 nextPoint = this.m_lstPoints[nextIndex];
//三点共线情况不存在，若三点共线则说明必有一点的y（斜线）或x（水平线）小于topPt
float r = NMath.CrossProduct((prePoint - topPoint), (nextPoint - topPoint));
if (r > 0)
{
return(true);
}
return(false);
}
