C# Raycasting / 从方向查找最近的矩形

Question

所以，我试图找到一种方法来找到我的点将击中的第一个矩形（从矩形列表中，所有 2D），沿着特定方向（在 C# 中），但是我似乎无法正确描述术语（如果有这样的东西，我发现最接近的东西是光线投射）。我的目标是从一个特定的“点”开始（在这种情况下，从下面的示例中可以看到星号-*），然后从那里选择一个特定的方向（左、右、下、上）（无角度）。所以假设我们选择 Down，那么它会命中的第一个矩形是“I'M A RECT 2”，因此应该返回这个。我已经知道矩形的所有位置和大小，所以我得到了这些信息。我该怎么做呢？     *       [I'M A RECT 1][I'M A RECT 2]                 [I'M A RECT 3][I'M A RECT 4]

Answer 1

您可以检查矩形是否可以与源自该点的射线相交，然后计算与 的距离point：

var point = new PointF(1.2f, 2.5f);

var rectangles = new RectangleF[]

{

    new RectangleF(1, 1, 1, 1),

    new RectangleF(3, 1, 1, 1),

    new RectangleF(5, 2, 1, 1),

};

var hit = rectangles

    .Select(x =>

    {

        if (IsBetween(point.X, x.Left, x.Left + x.Width))

            return new { Rectangle = x, Distance = GetClosestDistance(point.Y, x.Top - x.Height, x.Top) as float? };

        else if (IsBetween(point.X, x.Top - x.Height, x.Top))

            return new { Rectangle = x, Distance = GetClosestDistance(point.Y, x.Left, x.Left + x.Width) as float? };

        else return new { Rectangle = x, Distance = default(float?) };

    })

    .Where(x => x.Distance != null)

    .OrderBy(x => x.Distance)

    .FirstOrDefault()?.Rectangle;

bool IsBetween(float value, float lBound, float uBound) => lBound <= value && value <= uBound;

float GetClosestDistance(float value, float p0, float p1) => Math.Min(Math.Abs(p0 - value), Math.Abs(p1 - value));

编辑：

var hit = RayTest(point, rectangles, RayDirections.Right | RayDirections.Down) // or, try just `Down`

    .Where(x => x.Success)

    .OrderBy(x => x.Distance)

    .FirstOrDefault()?.Target;

[Flags]

public enum RayDirections { None = 0, Left = 1 << 0, Up = 1 << 1, Right = 1 << 2, Down = 1 << 3, All = (1 << 4) - 1 }

public class RayHit<T>

{

    public T Target { get; }

    public float? Distance { get; }

    public bool Success => Distance.HasValue;

    public RayHit(T target, float? distance)

    {

        this.Target = target;

        this.Distance = distance;

    }

}

public IEnumerable<RayHit<RectangleF>> RayTest(PointF point, IEnumerable<RectangleF> rectangles, RayDirections directions = RayDirections.All)

{

    if (directions == RayDirections.None)

        return Enumerable.Empty<RayHit<RectangleF>>();

    var ray = new

    {

        Horizontal = new

        {

            LBound = directions.HasFlag(RayDirections.Left) ? float.MinValue : point.X,

            UBound = directions.HasFlag(RayDirections.Right) ? float.MaxValue : point.X,

        },

        Vertical = new

        {

            LBound = directions.HasFlag(RayDirections.Down) ? float.MinValue : point.Y,

            UBound = directions.HasFlag(RayDirections.Up) ? float.MaxValue : point.Y,

        },

    };

    return rectangles

        .Select(x =>

        {

            float left = x.Left, right = x.Left + x.Width;

            float top = x.Top, bottom = x.Top - x.Height;

            if (IsBetween(point.X, left, right) && (IsBetween(top, ray.Vertical.LBound, ray.Vertical.UBound) || IsBetween(bottom, ray.Vertical.LBound, ray.Vertical.UBound)))

                return new RayHit<RectangleF>(x, GetClosestDistance(point.Y, bottom, top) as float?);

            else if (IsBetween(point.X, bottom, top) && (IsBetween(left, ray.Horizontal.LBound, ray.Horizontal.UBound) || IsBetween(right, ray.Horizontal.LBound, ray.Horizontal.UBound)))

                return new RayHit<RectangleF>(x, GetClosestDistance(point.Y, left, right) as float?);

            else return new RayHit<RectangleF>(x, default);

        });

    bool IsBetween(float value, float lBound, float uBound) => lBound <= value && value <= uBound;

    float GetClosestDistance(float value, float p0, float p1) => Math.Min(Math.Abs(p0 - value), Math.Abs(p1 - value));

}

注意：在这两个版本中，当点在矩形内时都会出现错误。计算的距离将是到最近边缘的距离，而不是 0 或负值。