/// <summary>
/// Returns the right-hand quadrant of the halfplane defined by the two quadrants,
/// or -1 if the quadrants are opposite, or the quadrant if they are identical.
/// </summary>
/// <param name="quad1"></param>
/// <param name="quad2"></param>
public static Quadrant CommonHalfPlane(Quadrant quad1, Quadrant quad2)
{
// if quadrants are the same they do not determine a unique common halfplane.
// Simply return one of the two possibilities
if (quad1 == quad2)
{
return(quad1);
}
int diff = (quad1.Value - quad2.Value + 4) % 4;
// if quadrants are not adjacent, they do not share a common halfplane
if (diff == 2)
{
return(Quadrant.Undefined);
}
var min = (quad1 < quad2) ? quad1 : quad2;
var max = (quad1 > quad2) ? quad1 : quad2;
// for this one case, the righthand plane is NOT the minimum index;
if (min == NW && max == Quadrant.SW)
{
return(Quadrant.SW);
}
// in general, the halfplane index is the minimum of the two adjacent quadrants
return(min);
}
/// <summary>
/// Returns whether this quadrant lies within the given halfplane (specified
/// by its right-hand quadrant).
/// </summary>
/// <param name="halfPlane"></param>
public bool IsInHalfPlane(Quadrant halfPlane)
{
if (halfPlane == SE)
{
return(this == SE || this == SW);
}
return(this == halfPlane || Value == halfPlane.Value + 1);
}
/// <summary>
/// Returns true if the quadrants are 1 and 3, or 2 and 4.
/// </summary>
/// <param name="quad">A quadrant</param>
public bool IsOpposite(Quadrant quad)
{
if (this == quad)
{
return(false);
}
int diff = (Value - quad.Value + 4) % 4;
// if quadrants are not adjacent, they are opposite
if (diff == 2)
{
return(true);
}
return(false);
}