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From: beeman@BOEING.COM (Roger Beeman)
Newsgroups: comp.sys.xerox
Subject: Re: Spaced-out Chat Fonts
Message-ID: <8712021929.AA07939@BOEING.COM>
Date: Wed, 2-Dec-87 14:29:32 EST
Article-I.D.: BOEING.8712021929.AA07939
Posted: Wed Dec  2 14:29:32 1987
Date-Received: Sat, 5-Dec-87 17:37:08 EST
Sender: usenet@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 23


David,

Chat, as you have observed, uses the SPACE character (0,040) to clear character
cells.  In Lyric, the font handling has changed such that when a strike for the
font is built, "excess" whitespace on the right side of the character bitmap is
truncated so that the width of the space provided by the font file is not
necessarily reflected in the strike that is constructed.  The strike is a
horizontal concatenation of the bitmaps for the characters within a character
set and is the source for the BITBLT's that display each character.  Seperate
metrics are maintained for the IMAGEWIDTH (width of the bits in the strike)
and the YWIDTH (distance to move the cursor to position for the next
character).  The VTCHAT terminal emulator uses (CHARWIDTH (CHARCODE A)) as the
width of the emulator's characters. 

Strikes are not rebuilt for fonts which are read in from files in the strike
format.  Thus this effect does not appear for GACHA 10 as you noted.

I have submitted a module to LispUsers called ANSICHAT which has a workaround
for this feature.

Office Systems Technology, Boeing Military Airplane Company
    Roger L. Beeman  beeman@boeing.com  (206) 394-3506