Mouse-hover tooltip with "values at current x coordinate" info

[Andreas N. <and...@gm...>]

Hi,

when I move my picker over the chart, the current values of the mouse
position are displayed.

For line series plots with many lines it would be useful to get a
grid-like table tooltip from the picker, that shows instead of current
cursor position effectively the same as the legend, yet additionally the
values of each line at the current x-position. Optionally, one may use
this feature to show values at current y-position.

This feature requires strictly monotonic values in the respective
coordinate direction.

Question: is there something already ready-made in QWT? If not, how
would I best implement it (without rewriting the entire legend
layout/drawing code)?

-Andreas