Re: The unwarranted scrolling assumption

[Eli Zaretskii]

> From: Lennart Borgman <address@hidden>
> Date: Thu, 17 Jun 2010 06:55:17 +0200
> Cc: Stefan Monnier <address@hidden>, address@hidden, address@hidden, 
>       address@hidden
> 
> > At least it works. I just tested. First time I am using Emacs without
> > "jumping scrolling"! :-)
> >
> > If you think this is the right way to fix it I will send patches later
> > when I cleaned up a bit.
> >
> > There is one more similar problem which I do not know how to handle,
> > in fileio.c. In the function Finsert_file_contents clip_changed is set
> > to 1. I am not quite sure of the impact of this but it looks wrong to
> > me to do this. I think the display engine should be told, but it must
> > decide what to do with redisplay, not fileio.
> 
> Here is the patch (without the fileio.c part which I leave until I got
> some comments).

This patch is not correct, IMO, because it does not consider the value
of the window's window_end_valid flag.  The function
reconsider_clip_changes, which you try to side-step, does the same as
this test in your patch:

> +  if ((buffer->clip_begv != buffer->begv) || (buffer->clip_zv != buffer->zv))
> +    buffer->clip_changed = 1;

but it also considers the window_end_valid flag, without which your
patched version could try reusing portions of the current glyph matrix
when the matrix is not guaranteed to be up to date.