bug#17678: 24.4.50; Feature Request -- calculate new `window-start` & `window-end` before visual redisplay

[Stefan Monnier]

> The display engine changes window-start for several reasons, only one
> of them being that point moved off screen.

Is there a comment somewhere that documents the cases where it can happen?

> I think follow-mode also needs to know when the window-end changes
> (which could happen with no changes in window-start).  This is
> normally known only at the end of window redisplay, IIRC.

In the case of follow-mode, I think the best way to handle that is to
make it possible for follow-mode to force redisplay to go through the
windows in a particular order.


        Stefan