Re: Redisplay problems with invisible text at the beginning of a line.

[Kim F. Storm]

Hi Lute,

I finally got around to look at these bugs, and I have just committed
some changes to CVS emacs which should fix these redisplay problems.

Can you pls. check whether there are still problems?   I found that
scrolling around in the master *info* buffer (C-h i) which has quite
some hidden text caused similar problems, but I don't see them after
installing the fix.


Lute Kamstra <address@hidden> writes:

> Dear people,
> 
> This concerns not only cvs Emacs 21.3.50 but also released Emacs 21.1
> and 21.3.  The bugs are slightly different for the released Emacsen,
> though.
> 
> Currently, I'm writing a major mode that uses an invisible character
> at the beginning of each line to store some data.  This results in a
> number of redisplay problems.  A good way to reproduce three of them
> is as follows:
> 
> Create a buffer in a window and make sure that the buffer is
> significantly larger that the window.  (Opening the tutorial with C-h
> t will do nicely.)
> 
> Move point to the first character of a nonempty line in the bottom
> half of the window.
> 
> Evaluate (put-text-property (point) (+ (point) 1) 'invisible t) to
> make the first character of the line invisible.
> 
> Type C-u 0 C-l (to invoke recenter).
> 
> What I would expect to see now is that the line the point is in would
> become the first line of the window and that point would not move.
> However, this is not the case.  Bug number 1:
> 
> A. For Emacs 21.1 and 21.3 the following happens.  The line point is
>    in, that is, the line starting with the invisible character,
>    becomes the first line of the window and point moves to the
>    beginning of the line in the middle of the window.
> 
> B. For Emacs 21.3.50 the following happens.  The line point is in
>    becomes the middle line of the window (as if C-l had been typed
>    without a prefix).
> 
> To see bug number 2, make sure that the line starting with the
> invisible character is the top line of the window and that point is in
> the line just after the top line.
> 
> Now type C-a followed by C-p.  I would expect that point would just
> move to the beginning of the top line.  This does happen, but the
> window is also redisplayed and the line point is in is now shown in
> the middle of the window.
> 
> For Emacs 21.1 under X (I can't test 21.3 or 21.3.50 under X at the
> moment) bug number 3 now occurs that does not happen on a console (-nw
> option).  The line starting with the invisible character that is shown
> in the middle of the window is followed by a copy of itself.  So the
> line line starting with the invisible character is displayed *twice*.
> Typing C-l at this time causes the copy to go away.
> 

-- 
Kim F. Storm  http://www.cua.dk