Re: font-backend mechanism on Windows and Mac?

[Kenichi Handa <handa@m17n.org>]

In article <46EA9371.7020701@gnu.org>, Jason Rumney <jasonr@gnu.org> writes:

> Kenichi Handa wrote:
> > Do you mean that the displaying got slower after the recent
> > change?

> Perhaps, it does seem a little slower, and the more complex clipping
> masks might have caused that, but I think most of the slowness is from
> the new font-backend itself. It seems to be outputting a character at a
> time, rather than whole lines. It might be due to a workaround in the
> Windows code to avoid a Cleartype bug in the old font code (though I'd
> expect the old code to be similarly slow in that case), or it might be
> not combining multiple redraw requests as the overlapping window is
> moved over the Emacs frame.

As I wrote before, metrics calculation is done one glyph by
one, but rendering is done for a block of glyphs (i.e. those
in one "struct glyph_string").

Anyway, while debugging the previous problem, I found that
the display engine (regardless of font-backend) does lots of
unnecessary clipping for exposing.  But, improving it
requires rather big changes.

---
Kenichi Handa
handa@m17n.org