Re: cursor doesn't show through transparent images in emacs 22, unlike emacs 21

[David Kastrup <dak@gnu.org>]

Richard Stallman <rms@gnu.org> writes:

>     There is no sensible default.  What is useful as a mask depends on the
>     image in question.  Using heuristic-mask can mean that the whole image
>     flashes, but it can also mean that just a single corner pixel blinks.
>
> 1. So what?  Another default can't be worse than the present one,
>    and it would be better MOST of the time.

The present setting results in almost all cases in a recognizable
cursor position (images with border 0 are possible only come Emacs
22.1).  The indication is not perfect in all cases, but vastly better
than a large flashing image.  Which would happen to be the result of
the new default in most cases.  I have experienced that: trust me,
this default _is_ worse, much much worse than the existing one.  The
existing one is quirky, your suggestion would be result in it becoming
horrible.

preview-latex had to go to quite disadvantageous techniques to avoid
large-scale flashing in Emacs 21.  You'd reintroduce it.

> 2. Maybe we need another possible :mask value which would specify
> drawing the cursor in the way that you suggested.

I think it would be a mistake to abuse :mask just in order to get the
cursor to display in a useful way.  In particular since it would mean
that customizing the cursor type would have no effect on images, and
all image managing software would have to implement their own idea of
a cursor.

> 3. If #2 is too complex to do now, maybe we should make it an error to
>    fail to specify :mask on an image on a character in the buffer.
>    That is simple.

It will also break wagonloads of existing code.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum