/// <summary>
/// Get the segment between each adjacent control points of current spline.
/// </summary>
/// <param name="self">The spline instance.</param>
/// <param name="index">
/// Index of the segment. The value can be -1 which means the segment formed by the extra head control point
/// and the first control point of the spline; and <see cref="ISpline.PointCount" />-1 which means the segment
/// formed by the last control point of the spline and extra tail control point.
/// </param>
public static Segment3 GetSegment(this ISpline self, int index)
{
var pc = self.PointCount;
if (index < -1 || index > pc - 1)
{
throw new ArgumentOutOfRangeException(nameof(index));
}
if (index == -1)
{
return(new Segment3(self.GetExtraHeadPoint(), self[0]));
}
if (index == pc - 1)
{
return(new Segment3(self[pc - 1], self.GetExtraTailPoint()));
}
return(new Segment3(self[index], self[index + 1]));
}