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

["Ken Manheimer" <ken.manheimer@gmail.com>]

On 8/27/06, Richard Stallman <rms@gnu.org> wrote:
>     > I think this means that if the image blocks out the background color,
>     > then the cursor won't appear.  Is that correct?  I think that is a problem.
>
>     Maybe -- but it's not a new problem.  It's the same as it was in 21.x, and
>     I don't recall any reports of that behaviour being a problem.
>
> How could it possibly not be a problem?  Is it that nobody uses
> non-transparent images?  Nobody cares about seeing the cursor in buffers
> that use non-transparent images?

i just experimented, filling in the transparent part of one of my
icons with a solid color.  the cursor still shows in that region,
instead of that color.

naturally figuring i made a mistake (as those of you reading this
probably do), i looked at the image with something else, and the solid
color showed where i put it.  i started twiddling with the image and,
doing an (clear-image-cache) after each change, discovered that if i
made the top-left and bottom-right corner pixels transparent, the
solid color showed as it should.  putting the solid color in one or
the other of those corners, however, causes emacs to treat it as
transparent, at least as far as showing the cursor in it.

(a bit more experimenting shows that the combinations of corners to
qualify a solid corner for treatment as transparent is a bit more
elaborate.  i'd like to see the algorithm, but satisfying that
curiousity is not sufficient reason to get acquainted with the display
system.  this behavior certainly doesn't satisfy the principle of
least surprise, and deserves some documentation, if it doesn't already
have it.)

the upshot is that the small glyphs will benefit from  kim's change,
even if they lack transparency, with the cursor color showing instead
of the color that occupies some combination of the corners -  or maybe
some other criteria, who knows.

-- 
ken
ken.manheimer@gmail.com
http://myriadicity.net