window-vscroll

window-vscroll is a built-in function in `C source code'.

(window-vscroll &optional WINDOW PIXELS-P)

Return the amount by which WINDOW is scrolled vertically.
If WINDOW is omitted or nil, it defaults to the selected window.
Normally, value is a multiple of the canonical character height of WINDOW;
optional second arg PIXELS-P means value is measured in pixels.