Re: Question about display engine

[martin rudalics]

>> Maybe we could start with a simple 'extend-face-background' option
>> (and add others if needed)?
>
> What about users who change the region or hl-line faces to use
> underlining?

Any underlining behavior would remain unaffected by setting
'extend-face-background'.  If both, underlining and background are
specified, the display engine would do what it does now.

> IOW, the problem with the attribute-level idea is that it will affect
> those attributes regardless of the face from which they came.

If the 'extend-face-background' is a simple boolean, yes.  If it is a
list of faces, it is largely idempotent to the face-level concept: A
user could say (by including or excluding) a face from that list
whether it should have any impact on extending the background to the
end of the window edge.  Just that the face merger would have to
process that variable if it is a list of faces while handling it in
the display engine would be sufficient for a boolean.

> So I now tend to think that if we consider some faces not eligible for

Didn't you mean to say "some face attributes not eligible" here ...

> extension, we should not extend any face attributes at all.  Too bad
> no one else except the 3 of us is talking in this thread; we need more
> opinions.

... because otherwise I don't see how we possibly could do that.  IIUC
the face merger would then have to decide whether "that" occurred.

martin