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List:       freedesktop-xorg
Subject:    Re: Xorg and Fonts
From:       Keith Packard <keithp () keithp ! com>
Date:       2005-08-31 18:00:24
Message-ID: 1125511225.4798.164.camel () evo ! keithp ! com
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On Wed, 2005-08-31 at 08:57 +0100, Glynn Clements wrote:
> Keith Packard wrote:
> 
> > Early estimates showed that total network traffic was a wash for Latin-1
> > fonts; server-side fonts must transmit all glyph metrics to the client
> > before any text drawing is done while client-side fonts must transmit
> > all used glyph images before drawing is done. Because client-side fonts
> > need only transmit the images actually used, this becomes even more
> > relevant when you start talking about larger fonts with significant
> > Unicode coverage.
> 
> How does this scale in the case where there are many clients all using
> the same font? Does the X server end up storing many copies of the
> same glyphs, or is there some mechanism by which common glyphs can be
> identified and shared?

The X server shares identical glyphs by hashing them into a global
table. What remains duplicated is the effort needed to rasterize the
glyphs in every client. Render provides mechanism for applications to
share entire glyphsets and hence avoid this effort, but nothing
currently takes advantage of this as it would significantly complicate
application implementation.

-keith


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