c# null for System.drawing.PoinF

Question

I'm using C# for grphics. And now I want to return a null for PointF

    /// <summary>
    /// Project the point according to camera position.
    /// </summary>
    /// <param name="p">Point position, in WC</param>
    /// <returns>pixel position</returns>
    public PointF Project(MCvPoint3D32f p)
    {
        //return new PointF(p.x, p.y);
        // Extend p
        Matrix<double> p_ex = new Matrix<double>(3, 1);
        p_ex[0, 0] = p.x;
        p_ex[1, 0] = p.y;
        p_ex[2, 0] = p.z;

        var rst = HomographMatrix * p_ex;
        rst[0, 0] = rst[0,0] / rst[2, 0] * focalLength * scale;
        rst[1, 0] = rst[1, 0] / rst[2, 0] * focalLength * scale;

        return new PointF((float)rst[0, 0], (float)rst[1, 0]);
    }

Here I want to return a 'null' for the point if the point is out of FoV of my camera. But actually PointF is not 'nullable', so is there a straight forward way to return a 'null' for the point?

I don't want to inherit the native PointF.

Answer 1

In some ways this depends on your requirements. For example, if you need to store lots of points (so space is a factor), you could use some kind of sentinel value - perhaps:

static readonly PointF NilPoint = new PointF(float.NaN, float.NaN);

then check for that runtime, perhaps with a helper method:

public static bool IsNil(this PointF value)
{
    return float.IsNaN(value.X) || float.IsNaN(value.Y);
}

so you can just check:

if(!point.IsNil()) {
    // etc   
}

However, an easier option (with a slight space overhead) is just to use Nullable<T>, i.e.

PointF? pt1 = null; // fine
PointF? pt2 = new PointF(123,456); // also fine