C# Raycasting / 从方向查找最近的矩形

Question

所以，我正在尝试找到一种方法来找到我的 Point 将命中的第一个 Rectangle（从矩形列表中，全是 2D），进入一个特定的方向（在 C# 中），但是我似乎无法正确描述术语（如果有这样的事情，我发现最接近的是光线投射）。

我的目标是从一个特定的“点”开始（在这种情况下，星号- * 从下面的示例中看到），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 rect 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？

     *       [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point的距离：

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。