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List:       xfree-fonts
Subject:    Re: [Fonts] Complex text layout and mapping screen coordinates
From:       Keyur Shroff <keyur_shroff () yahoo ! com>
Date:       2002-02-26 4:49:32
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--- Brian Stell <bstell@ix.netcom.com> wrote:

> > True. What's wrong with the client doing the layout,
> but using the
> > "services" of the X server for handling the information
> in the open type
> > font file ? 
> 
> TrueType/OpenType font are beginning to have positioning 
> information in them in the GPOS table.
> 
> How will the X client get the GPOS information in the
> TrueType
> font if the font is handled on the X server?

We need positioning information for (a) drawing glyph at
proper position (b) getting proper text extents for a
string.

For (a), server side approach actually reduces the traffic
because it is responsible for drawing each glyph at proper
position and client only have to pass entire string (upto
line break) in a single request. In client side approach,
since client has to find relative (x,y) position for each
glyph from GPOS table, a separate request need to be sent
for each character (or glyph?) code over the wire.

For (b), again only one request need to be sent for each
run in the string. Client can maintain cache (as it is
doing in Gtk) so that we can send request for querying text
extents only when text string is modified. Also only part
of the string will be queried (two or three request are
necessary at a time) to find new extents and update the
cache. For client side approach no request will be sent for
finding text extents but we have to send a separate request
to draw glyph for all characters starting from the
modification point. This actually increases network
traffic. Parsing OpenType tables on the client side again
increases this overhead.

- Keyur



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