Getting the selected value from a Plot

[Kerollmops]

Hey,

I would like to know if there is a way to get the value that has been auto-snap-selected by egui when the cursor moves nearby.
I know that we can get the exact position of the cursor by using PlotUi::pointer_coordinate but it is not exactly what I would like.

For example on this screenshot, my cursor is at something like 30px from the auto-snap-selected value.

[lordbenedikt]

I have the same problem.

[Peepo-Juice]

I'm working on something right now and would like this feature as well.

[haricot]

I propose a pull request #2572 that covers this aspect, it not directly retrieve the pointer coordinate selected by the radius but give if is_in_radius, hovered indexes and item name hovered after that you can retrieve information about the selected value from a item Plot.

[Turun]

You can use Plot::label_formatter() as a workaround. This method is called in order to determine what should be written in the little popup and therefore contains the coordinates of the point you are interested in.

The obvious implementation of this workaround - cloning the PlotPoint parameter given in the label_formatter closure - doesn't compile, however. The rust compile can not guarantee that the closure will live shorter than the parameter you want to copy it to. So you need to pass a static variable or something else owned into the closure that can report back the value of the PlotPoint parameter whenever the closure is run (as far as the compiler is concerned it may be stored and executed much later, after the current call of App::update already terminated and your extraction variable is dropped).
I used a channel for that. It's very hacky, but it works. It also allows me to check if the crosshair is not painted in the plot this frame. Very important if you can not afford to work with outdated information about the crosshair from a previous frame.

My solution looks like this:

let (tx, rx) = mpsc::channel::<PlotPoint>();
let plot_response = Plot::new("known implants plot")
    .label_formatter(move |_name, value| {
        let _response = tx.send(value.clone());
        format!("x={value.x}\ny={value.y}")
    })
    .show(ui, |ui| { ui.points(points) } );

let crosshair: PlotPoint = if let Ok(value) = rx.recv() {
    Some(value)
} else {
    // nothing was sent, e.g. because the user doesn't hover the plot
    None
};

Additionally, you can check if the crosshair is snapped to a plot item or not by doing:

let mouse_position = plot_response.response.hover_pos();
if let Some(crosshair) = crosshair {
    // check if the position of the mouse and the position of the crosshair
    // are identical (in screenspace here, but plotspace should work too)
    let crosshair_is_snapped = mouse_position != plot_response.transform.position_from_point(&crosshair);
}