Re: region-based face-remapping

[Dmitry Gutov]

On 03/01/2024 15:42, Eli Zaretskii wrote:
> > Date: Wed, 3 Jan 2024 14:40:49 +0200
> > Cc:emacs-devel@gnu.org
> > From: Dmitry Gutov<dmitry@gutov.dev>
> >
> > On 03/01/2024 14:31, Eli Zaretskii wrote:
> > > The workhorse we use now for obtaining face information is the
> > > function face_at_buffer_position, which calls the various face-merging
> > > routines.  Those merging routines and their subroutines consider
> > > face-remapping-alist as part of face merging process outlined above.
> > > I don't see how we can avoid passing the buffer position to them if
> > > face-remapping depends on buffer position.
> > Perhaps face_at_buffer_position would first look up the overlay/text
> > property 'face-remapping-alist, then merge its value with the variable
> > face-remapping-alist (using plain 'append', for example), and pass on
> > the resulting value to the face-merging routines?
> Then any code running while face_at_buffer_position does its job will
> see a tweaked value of face-remapping-alist, which is not necessarily
> TRT, since it is not guaranteed that the buffer position being
> examined by face_at_buffer_position is relevant to the rest of the
> code.

I'm not sure I understand your response.

IIUC the request is that one would be able to change the faces' 
appearances at any position in the buffer using a mechanism like 
additional text properties or overlay properties.

It seems to reason that any code computing the 'face' for a buffer 
position would need to account for the new property if it's set at that 
position.