Re: Bug in incremental undrawing of mouseover highlighting

[David Kastrup <dak@gnu.org>]

Bob Rogers <rogers-emacs@rgrjr.dyndns.org> writes:

>    It seems that mouseover background highlighting is not undrawn if
> replaced by the same unhighlighted text.  This happens in the CVS
> version as of late on 11-Nov.  (I have seen this bug for some time now,
> but only just thought of a (relatively) easy way to reproduce it.)
>
>    To reproduce:
>
>    1.  "emacs -Q"
>
>    2.  "C-x d RET".  This gets a dired buffer; the exact directory
> doesn't matter as long as it has at least a few files in it.  (And, for
> some reason, "." and ".." don't count.)
>
>    3.  "C-x h M-w C-x b *scratch* RET C-y M-<".  This gets a copy of the
> dired buffer contents; sometimes they come with dired fontification, and
> sometimes not.  The same text should be displayed in the same character
> positions in both dired and *scratch* buffers.
>
>    4.  "C-x b RET" to get back to the dired buffer, and move the mouse
> over a file name so that it is highlighted in green.
>
>    5.  "C-x b RET" to return to *scratch*.  Notice that the same
> characters in the same position are still highlighted in green.
>
>    6.  Move the mouse to a different file name.  Usually the
> highlighting goes away, but sometimes it doesn't (and it doesn't
> correlate with fontification).  If it does persist, type "C-x b RET" to
> return once more to the dired buffer, and there will be two green file
> names -- this can be repeated until every file name is green.

For people wanting to debug this: I have the slight suspicion that the
problem is masked usually because some well-meaning workaround
suppresses the highlighting of partial lines that _should_ be
highlighted when a buffer pops up under the mouse cursor.  Often the
highlighting only starts once one moves the mouse cursor.  And I think
that the problem might be triggered when only parts of the line are
to be highlighted.

I have no recipe for reproduction now, this is rather irregular and
tends to occur in the newsreader for me, which means that there is no
repeatable recipe.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum