Hi @swharden,

I looked at your work and want to leave a few comments.

1. Do we really need to support a unique cursor for each Plottable on the MouseOver event? It's hard for me to imagine such scenarios. Everything would be greatly simplified if this cursor were set the same in the Control itself.
2. IHittable may contain the ability to disable clicks by analogy with IDraggable.

public interface IHittable
{
  bool ClickEnabled {get; set};
  //or
  bool HitTestEnabled{get;set;}
...
}

3. You will not need to save the state in the plottable if you also transfer the current Plot.Dims to HitTest(), which are already saved. The hit calculation will be done every time HitTest() is called and it needs to be fast to be able to bind it to OnMouseMove events.

public bool HitTest(Coords c, PlotDimensions dims);

4. We can play a bit with linq to shorten the code:

public IPlottable GetHittable(double xPixel, double yPixel)
{
    return GetPlottables()
               .Where(x => x is IHittable)
               .Reverse())
               .FirstOrDefault( p => 
                {
                    double xCoords = GetCoordinateX((float)xPixel, p.XAxisIndex);
                    double yCoords = GetCoordinateY((float)yPixel, p.YAxisIndex);
                    Coordinate c = new(xCoords, yCoords);
                    
                    return  (IHittable)p.HitTest(c);         
                });
}

Hi @StendProg, thank you for your feedback! I really value your input. I found this problem to be surprisingly difficult, and it I put it down for a few days and am now coming back to it.

1. Do hittable plottables require unique cursors?

I think so. Here are some potential use cases.

2. HitTestEnabled

public interface IHittable
{
  bool HitTestEnabled { get; set; }
...
}

Great suggestion! I will implement this.

3&4. Instead of storing state, can you pass dims into HitTest()?

The hit calculation will be done every time HitTest() is called and it needs to be fast to be able to bind it to OnMouseMove events.

Unfortunately the size of bounding box requires string measurement, and that is costly enough that I don't think it is worth performing on every mouse move event. Not finding a better solution this problem is why I put this PR down and haven't picked it up in two weeks 😅 It is much more difficult than I initially thought it would be. I can't think of a better way to achieve this, but after I merge this I welcome additional thoughts you have or suggestions for improvements here or in #1844.