bug#67794: 30.0.50; mouse-face is not respected on SVG images

[Alan Third]

On Mon, Dec 18, 2023 at 07:36:49PM +0100, Manuel Giraud wrote:
> Alan Third <alan@idiocy.org> writes:
> 
> > If that's not happening then there must be a bug somewhere.
> >
> >> It does something on the an image glyph when it is hover but the image
> >> is completely messed up.  I have stepped this code down to
> >> svg_load_image but I do not understand what went wrong.  Any ideas?
> >
> > The code looks OK to me. In what way is the image messed up? I'm not
> > sure how to test mouse face on my machine, is there a built-in theme
> > that uses it?
> 
> The image contains some random pixels that look like part of previously
> loaded picture.  You could try it with the previous patch and test it
> with the following command:

Thanks, that worked. It was fine in NS (under GNUstep no less! It's
unusual for GNUstep to work when other things don't) but failed under
GTK/Cairo.

I believe that we need to do some final set-up for the image under
X/GTK/whatever and it looks as though this is all that's needed:

     id = lookup_image (f, s->img->spec, hlinfo->mouse_face_face_id);
     s->img = IMAGE_FROM_ID (f, id);
     prepare_image_for_display (f, s->img); <------

Under X we need to send the image to the X server, and under Cairo it
does some other stuff. That's what prepare_image_for_display does. It
does nothing under NS, so the image worked fine under GNUstep.
-- 
Alan Third