Introduce type parameter for plot points

[ghost]

In order to supply custom data to plot points for use mainly in the label_formatter this introduces a new field which stores userdata.

Hovering over a plot point	Hovering over anything else

Of course this requires PlotPoint to have a generic type parameter which then requires lots of other structs to be generic too.

The userdata field is optional, since a PlotPoint can be a Point supplied by the user when constructing a plot item, but it can also be generated by the library.

A demo for this is implemented as you can see in the screenshot.

Of course I would like there to be an easier way to do this, but currently I'm not aware of any.

[Mingun]

At least, you can make generic parameters optional (<T = ()>)

[ghost]

Yes thats a good Idea, but when I did that I realized that the default type parameter only applies when you use <T> and not T itself.

See rust-lang/rust#36980.

[emilk]

I'm not a big fan of adding templates to everything. It not only makes the core more complex, it also means monomorphization will duplicate the code in the binary, ballooning e.g. the .wasm size.

If you want to attach user-data to points, I suggest you report Points::id together with the point index (usize) to the user. The user can then look up the data they need with a hashmap or similar.

[ghost]

@emilk I tried it and it works with only a few modifications to the library.
But it is quite cumbersome to use, since you need an Arc<Mutex<...>> for the label_formatter and the plot_ui to be able to use the same HashMap. This also requires you to create or at least re-fill the HashMap on every draw...

Is this what you had in mind or is there a simpler way to do this?

[emilk]

egui_plot has recently been moved to its own repository, at https://github.com/emilk/egui_plot

This will hopefully speed up its development by having more reviewers and maintainers.

Please re-open this PR at https://github.com/emilk/egui_plot/pulls

See also:

• Looking for maintainer egui_plot#58
• Move egui_plot to its own repo #4828