Output pane Scolling

Hi all,

I'm trying to display large files with embedded graphics (such as colored
rectangle around text and so on).

I'm using an output pane and trying to refresh its contents as the user move
the scrollbar (like in the example ./capi/output-panes/scroll-test.lisp).

Q1) I would like the slug-position to be sync with the line-number of my
large file, instead of being expressed in pixels. Is that possible ?

Q2) What is the purpose of the capi::scroll-vertical-slug-size,
capi::scroll-vertical-slug-size-tracking ? (seen in "internal scroll
geometry")

Thanks,
Sebastien.