/// <summary>
/// -1 => right turn
/// 0 => no turn
/// 1 => left turn
/// </summary>
public static int TurnTest(VecRat2 a, VecRat2 b, VecRat2 c)
{
//return Rational.Sign(a.X * b.Y + a.Y * c.X + b.X * c.Y - a.X * c.Y - a.Y * b.X - b.Y * c.X);
VecRat2 u = b - a;
u = new VecRat2(u.Y, -u.X); //turn to right 90 degrees
Rational udota = u.X * a.X + u.Y * a.Y;
Rational udotc = u.X * c.X + u.Y * c.Y;
return(udota.CompareTo(udotc));
}
public int CompareTo(OA_Segment other)
{
if (!(this.IntersectsSweepline && other.IntersectsSweepline))
{
throw new InvalidOperationException();
}
if (this == other)
{
return(0);
}
Rational thisX = this.SweeplineIntersectionX;
Rational otherX = other.SweeplineIntersectionX;
int comp = thisX.CompareTo(otherX);
if (comp != 0)
{
return(comp);
}
//The downward ordering
Turn turn = MathAid.TurnTestDiscrete(this.Upper.Position, new VecRat2(thisX, Sweepline.Y), other.Upper.Position);
if (turn == Turn.Linear)
{
turn = MathAid.TurnTestDiscrete(this.Lower.Position, new VecRat2(thisX, Sweepline.Y), other.Lower.Position);
}
if (turn == Turn.Right)
{
comp = -1;
}
else if (turn == Turn.Left)
{
comp = 1;
}
else
{
//Two segments overlapping at more than a single point
comp = 0;
}
//We know thisX==otherX
//We want the downward ordering if these segments cross to the left of the current event point
//However, if:
// a) the sweepline is before the event point and these segements pass through the event point
// or b) these segments cross to the right of the current event point
//Then we want to reverse this ordering!
if ((Sweepline.BeforeEventPoint && thisX == Sweepline.IncidentEventPoint.Position.X) ||
thisX > Sweepline.IncidentEventPoint.Position.X)
{
comp *= -1;
}
if (comp != 0)
{
return(comp);
}
comp = this.Upper.CompareTo(other.Upper);
if (comp != 0)
{
return(comp);
}
comp = this.Lower.CompareTo(other.Lower);
return(comp);
//comp = this.Upper.Position.Y.CompareTo(other.Upper.Position.Y);
//if (comp != 0)
// return comp;
//comp = this.Upper.Position.X.CompareTo(other.Upper.Position.X);
//if (comp != 0)
// return comp;
//comp = other.Lower.Position.Y.CompareTo(this.Lower.Position.Y);
//if (comp != 0)
// return comp;
//comp = other.Lower.Position.X.CompareTo(this.Lower.Position.X);
//return comp;
}
