OverflowException

OverflowException
AwesomeNamespace.UniformPoissonDiskSampler.Sample (UnityEngine.Vector2 topLeft, UnityEngine.Vector2 lowerRight, System.Nullable`1[T] rejectionDistance, System.Single minimumDistance, System.Int32 pointsPerIteration) (at Assets/PanoramaTerrainTools/ToolExtended/UniformPoissonDiskSampler.cs:61)

почему settings.GridWidth318settings.GridHeight-325 вызывает Исключение переполнения ? Ошибка в этой строчке:

    var state = new State
    {
        Grid = new UnityEngine.Vector2?[settings.GridWidth, settings.GridHeight],
        ActivePoints = new List<UnityEngine.Vector2>(),
        Points = new List<UnityEngine.Vector2>()
    };

Весь метод :

struct State
{
    public UnityEngine.Vector2?[,] Grid;
    public List<UnityEngine.Vector2> ActivePoints, Points;
}
static List<UnityEngine.Vector2> Sample(UnityEngine.Vector2 topLeft, UnityEngine.Vector2 lowerRight, float? rejectionDistance, float minimumDistance, int pointsPerIteration)
{
    var settings = new Settings
    {
        TopLeft = topLeft, LowerRight = lowerRight,
        Dimensions = lowerRight - topLeft,
        Center = (topLeft + lowerRight) / 2,
        CellSize = minimumDistance / SquareRootTwo,
        MinimumDistance = minimumDistance,
        RejectionSqDistance = rejectionDistance == null ? null : rejectionDistance * rejectionDistance
    };
    settings.GridWidth = (int) (settings.Dimensions.x / settings.CellSize) + 1;
    settings.GridHeight = (int) (settings.Dimensions.y / settings.CellSize) + 1;
    Debug.Log("settings.GridWidth"+settings.GridWidth+"settings.GridHeight"+settings.GridHeight);
    var state = new State
    {
        Grid = new UnityEngine.Vector2?[settings.GridWidth, settings.GridHeight],
        ActivePoints = new List<UnityEngine.Vector2>(),
        Points = new List<UnityEngine.Vector2>()
    };

    AddFirstPoint(ref settings, ref state);

    while (state.ActivePoints.Count != 0)
    {
        var listIndex = RandomHelper.Random.Next(state.ActivePoints.Count);

        var point = state.ActivePoints[listIndex];
        var found = false;

        for (var k = 0; k < pointsPerIteration; k++)
            found |= AddNextPoint(point, ref settings, ref state);

        if (!found)
            state.ActivePoints.RemoveAt(listIndex);
    }

    return state.Points;
}