private static Dir4 GetNormal(Loc invEntry, Loc invExit, Multiplier entryX, Multiplier entryY)
{
if (entryX > entryY)
{
return((invEntry.X < 0) || (invEntry.X == 0 && invExit.X < 0) ? Dir4.Right : Dir4.Left);
}
else if (entryX < entryY)
{
return((invEntry.Y < 0 || (invEntry.Y == 0 && invExit.Y < 0)) ? Dir4.Down : Dir4.Up);
}
else
{
return(Dir4.None);
}
}
private static Hit ResolveNarrow(Loc origin1, Loc origin2, Loc destination, Rect other)
{
var velocity = (destination - origin1);
Loc invEntry, invExit;
Multiplier entryX, entryY, exitX, exitY;
if (velocity.X > 0)
{
invEntry.X = other.Left - origin2.X;
invExit.X = other.Right - origin1.X;
}
else
{
invEntry.X = other.Right - origin1.X;
invExit.X = other.Left - origin2.X;
}
if (velocity.Y > 0)
{
invEntry.Y = other.Top - origin2.Y;
invExit.Y = other.Bottom - origin1.Y;
}
else
{
invEntry.Y = other.Bottom - origin1.Y;
invExit.Y = other.Top - origin2.Y;
}
if (velocity.X == 0)
{
entryX = Multiplier.MinValue;
exitX = Multiplier.MaxValue;
}
else
{
entryX = new Multiplier(invEntry.X, velocity.X);
exitX = new Multiplier(invExit.X, velocity.X);
if (entryX > new Multiplier(1, 1))
{
entryX = Multiplier.MaxValue;
}
}
if (velocity.Y == 0)
{
entryY = Multiplier.MinValue;
exitY = Multiplier.MaxValue;
}
else
{
entryY = new Multiplier(invEntry.Y, velocity.Y);
exitY = new Multiplier(invExit.Y, velocity.Y);
if (entryY > new Multiplier(1, 1))
{
entryY = Multiplier.MinValue;
}
}
var entryTime = Multiplier.Max(entryX, entryY);
var exitTime = Multiplier.Min(exitX, exitY);
if ((entryTime > exitTime || entryX == Multiplier.MinValue && entryY == Multiplier.MinValue) ||
(entryX == Multiplier.MinValue && (origin2.X < other.Left || origin1.X > other.Right)) ||
entryY == Multiplier.MinValue && (origin2.Y < other.Top || origin1.Y > other.Bottom))
{
return(null);
}
var result = new Hit()
{
Amount = entryTime,
Position = origin1 + velocity * entryTime.Numerator / entryTime.Denominator,
Normal = GetNormal(invEntry, invExit, entryX, entryY),
};
return(result);
}
