`window-absolute-pixel-position' with vscroll

[Rahguzar]

Hi all,
Reading the manual and documentation I understand the
`window-absolute-pixel-position' if there is no vscroll. If however the
value of `(window-vscroll)` is non-nil calling

(window-absolute-pixel-position (window-start))

produces results which I don't know how to interpret since the upper
left corner of the line is not visible. I wanted to know the pixel
position of the start of some subsequent visible line but results of
`(window-absolute-pixel-position pos)' didn't make sense to me. I
eventually managed to do it by using a combination of
`pos-visible-in-window-p' and `line-pixel-height' but maybe there is a
simpler way using `window-absolute-pixel-position'.

Thanks in advance,
Rahguzar