How do I select a line by clicking in Makie?

Question

I want to be able to select a line on the plot by clicking on it. Ideally, when I click on any line, the number of that line will appear on the screen. I wrote my code based on the tutorial, but there is no example with lines, so I did what I did. https://docs.makie.org/v0.19/documentation/events/index.html#point_picking

At the moment I have no idea what these numbers are telling me and why. They are not even coordinates of clicked points.

P.S. Actually it is just a starting point. I want to create event interaction on series and topoplots. But for now it would be great to find out the basics.

f = Figure(backgroundcolor = RGBf(0.98, 0.98, 0.98), resolution = (1500, 700))
ax = Axis(f[1, 1], xlabel = "Time [s]", ylabel = "Voltage amplitude [µV]") 

N = 1:length(pos)
positions = Observable(rand(Point2f, 10))

xs = 0:0.01:10
ys = 0.5 .* sin.(xs)

lines!(xs, ys)
lines!(xs, ys * 2)

hidedecorations!(ax, label = false, ticks = false, ticklabels = false) 
hidespines!(ax, :t, :r) 
hlines!(0, color = :gray, linewidth = 1)
vlines!(0, color = :gray, linewidth = 1)

i = Observable(0)
on(events(f).mousebutton, priority = 2) do event
    if event.button == Mouse.left && event.action == Mouse.press
        plt, i[] = pick(f)
        str = lift(i -> "$(i)", i)
        text!(ax, 1, -0.5, text = str,  align = (:center, :center)) 
    end
end
f

Below are some examples of the interaction between clicking and the number displayed (the red dot is where I click).

Answer 1

Check out the mouseposition variable here:

https://docs.makie.org/stable/api/#Events

or the registerInteraction! function here:

https://docs.makie.org/v0.19/examples/blocks/axis/index.html#registering_and_deregistering_interactions

You can use them both as below:

using GLMakie

f = Figure(backgroundcolor = RGBf(0.98, 0.98, 0.98), resolution = (1500, 700))
ax = Axis(f[1, 1], xlabel = "Time [s]", ylabel = "Voltage amplitude [µV]") 

#N = 1:length(pos)
positions = Observable(rand(Point2f, 10))

xs = 0:0.01:10
ys = 0.5 .* sin.(xs)

lines!(xs, ys)
lines!(xs, ys * 2)

hidedecorations!(ax, label = false, ticks = false, ticklabels = false) 
hidespines!(ax, :t, :r) 
hlines!(0, color = :gray, linewidth = 1)
vlines!(0, color = :gray, linewidth = 1)

register_interaction!(ax, :my_interaction) do event, axis
    if event.type === MouseEventTypes.leftclick
        println("Graph axis position: $(event.data)")
    end
end

i = Observable(0)
on(events(f).mousebutton, priority = 2) do event
    if event.button == Mouse.left && event.action == Mouse.press
        plt, i[] = pick(f)
        str = lift(i -> "$(i)", i)
        text!(ax, 1, -0.5, text = str,  align = (:center, :center)) 
        @show mouseposition(f)
    end
end
f

Note that for some reason (perhaps it sees the first click as a selection?) Makie does not start registering the interaction on the graph until the first click within the graph, unlike the clicks on the figure which are all shown even the first one.