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Working paper 78: FED, the Font "EDitor".

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.xgp
.font 0 25vg
.font 1 s25xif
.font 2 25vmic
.font 3 40vshd
.ulfont 87
.squish
.topm 50
.sidm 50
.spw 16
.he1
FED and Font Formats
.nf
.in 38
2Massachusetts Institute of Technology
Artificial Intelligence Laboratory0
.in 0
.sp 5
.spread
/3WORKING PAPER #780//(revision 1)/
.ri
8 October, 1975
.sp 4
.ce
FED, the Font "EDitor"
.center
and
.center
Font Formats
.center
by
.center
Joseph D. Cohen and J. Pitts Jarvis
.sp 6
.center
Abstract
.adjust
This memo describes
FED, a program used for compiling and inspecting fonts;
AST font format, a text format which can be used to create and edit fonts;
and KST font format, the binary format used by SCRIMP, TJ6, and PUB.
.sp 6
Work reported herein was conducted at the Artificial Intelligence
Laboratory, a Massachusetts Institute of Technology research program
supported in part by the Advanced Research Projects Agency of the
Department of Defense and monitored by the Office of Naval Research
under Contact number N00014-70-A-0362-0005.
.sp
Working Papers are informal papers intended primarily for internal use.
.he2
Font Editor and Console Operation.
.pa
.sect
FED, the Font "EDitor"
.sp
FED is a program used for compiling and inspecting fonts.
FED understands the following font formats:
.in 16
.un 8
AST -- text format which can be used to create and edit fonts in TECO;
.un 8
KST -- MITAI and CMU compiled font format, used by programs like SCRIMP, TJ6, and PUB;
.un 8
CMU -- a newer compiled CMU format;
.un 8
CU -- the newest compiled CMU format;
.un 8
FNT -- SAIL compiled font format; and
.un 8
XH -- Xerox PARC compiled font format.
.in 0
FED reads all formats, but writes only AST and KST.
.sp
FED asks for an input file name. If the second name is AST, KST, FNT, or XH,
FED assumes the input file to be in the appropriate format. If the second name
is something else, FED asks what FORMAT the input file is in.
If the file name is blank, FED kills itself.
FED reads the file and types out various decimal data.
A FIXED width font is one in which the CHARACTER WIDTH of all defined characters is the same as
the CHARACTER WIDTH of a space.
FED calls all other fonts VARIABLE width.
.sp
FED tries to display the font on the user's terminal, if it's a TV display;
or on the 340, if the user is near there, and the 340 and PDP6 are available.
FED displays as though one XGP dot equals one display dot, so the size and proportion
of the font will be distorted.
(200 horizontal XGP dots = 1 inch, 192 vertical dots = 1 inch.
~108 horizontal 340 dots = ~108 vertical 340 dots = 1 inch.
~58 horizontal TV display dots = 1 inch. ~57 vertical TV display dots = 1 inch.
A TV font display will therefore be enlarged 4 diameters over the same
font on the XGP.)
.sp
FED then offers to write out the font.
If you type N, FED restarts itself; if
you type Y, it asks for the output file name; and if anything else is typed, it repeats
its offer.
If you write the file, FED will offer to compact the raster.
(This is a horizontal compaction accomplished by eliminating leading
and trailing blank columns.) If you type Y, FED will compact the raster
as much as possible, and tell you how many words the compaction will
save in the XGP's PDP11. When compacting, FED will also let you know
if there are any characters whose raster is wider than the defined
raster width.
The input default system name is FONTS, the output default system name is
the job's SNAME.
Input and output default second file name is KST.
.sp
Please do not write new fonts onto the FONTS directory --
it is almost full. Absolutely do not modify
fonts on the FONTS directory. All concerned programs are perfectly capable of reading
fonts from your very own directory. The reason for this injunction is that it has
been determined, after much experimentation, that the definition of "improvement" is
consistently a local variable. Please keep your "improvements" to yourself.
.sp
.block 23
A typical FED console session looks as follows:
(User typein is underlined, 1î0 is a carriage return.)
.nf
1:fedî
FED 119
INPUT: jdc;ast >î
FORMAT: kstî
READING: DSK:JDC;AST 25
142 DUPLICATE CHARACTER
FILE: DSK:JDC;AST 25
KSTID: 0
CHARACTERS READ: 128
HEIGHT: 25
WIDTH: (VARIABLE)10
WRITE? (Y OR N)y
FILE: ast kstî
FILE ALREADY EXISTS. CLOBBER? (Y OR N)y
WRITING: DSK:JDC;AST KST
COMPACT RASTER? (Y OR N)y
2032 (OCTAL) PDP11 WORDS SAVED
INPUT: î
:KILL0
.ad
.he2
AST Font Format
.pa
.sect
AST Font Format
.sp
The AST font format is a text format which can be used to
create and edit fonts in TECO. An AST file has one page of font data, followed by
one page of character data for each defined character. All numbers except
CHARACTER CODE are decimal.
It is the order of the numbers, rather than
the text identification after them, that FED looks at.
The identification is merely a convenience.
.sp
The file's first page is font data and looks like:
.nf
1n KSTID dev:dir;file name
n HEIGHT
n BASE LINE
n COLUMN POSITION ADJUSTMENT0
.sp
.ad
.in 8
.un 8
1KSTID0 is a currently unimplemented feature. It is intended to be a unique number
for each font so that PDP11 will know which fonts are loaded,
and not do unnecessary reloads.
KSTID is used by CMU. (KSTID should be set to 0.)
FED writes, on every page of the output AST file, the file name of the
source font file. On input FED ignores the file name data in AST files.
.un 8
1HEIGHT0 is the height of all characters in XGP raster lines.
.un 8
1BASE LINE0 is the location of the character base line in XGP raster
lines from the top of
all characters. (The base line is used by the XGP underscore command.
See Working Paper #72, XGP Font Catalog.)
.un 8
1COLUMN POSITION ADJUSTMENT0 is an artifact. It is a
number which is added to the LEFT KERN of each character to get its total left kern.
To be SAIL compatible, COLUMN POSITION ADJUSTMENT should be 0, and all kerning
sould be included
in individual character data.
.in 0
.sp
The rest of the file is one page of character data for each defined character.
Each page looks like:
.nf
1n CHARACTER CODE
n RASTER WIDTH
n CHARACTER WIDTH
n LEFT KERN
* *
* *
*
* *
* *0
.sp
.ad
.in 8
.un 8
1CHARACTER CODE0 is the octal ASCII code of the character.
.un 8
1RASTER WIDTH0 is the width of the raster in XGP dots.
It is a good idea to make the raster width as small as possible,
in order to save space in font files, and to allow the XGP PDP11 to
store more fonts.
A leading blank column can be flushed if RASTER WIDTH and LEFT KERN are
decremented. Trailing blank columns can be flushed by simply decrementing RASTER WIDTH.
(The FED compact feature does this automatically.)
.un 8
1CHARACTER WIDTH0 is the amount, in XGP dots, that printing this character will
advance the line postion.
This number is completely independent of RASTER WIDTH, and LEFT KERN.
For example, if CHARACTER WIDTH<RASTER WIDTH,
characters will overlap.
If CHARACTER WIDTH>RASTER WIDTH, there will be extra
blank columns in the character. How many appear on each side is determined
by LEFT KERN.
.un 8
1LEFT KERN0 (plus COLUMN POSITION ADJUSTMENT, if any) is the amount to move left
from the logical left end of the character before printing the raster.
(Positive left kern means move left; negative, move right.)
.un 8
1*0 is any printing character used to define the CHARACTER RASTER.
Each raster row is represented by a text line.
If a space appears, the bit is off in the
raster, if a printing character appears, the bit is on. Carriage return terminates the
text row, and implies blanks for the rest of the raster row.
Formfeed terminates the raster, and implies trailing blank raster lines.
The first row is the top row. Information wider than
RASTER WIDTH is ignored.
.in 0
.he2
KST Font Format
.pa
.sect
KST Font Format
.sp
KST is CMU's oldest and MITAI's only compiled binary font format.
SCRIMP, TJ6, PUB, and other programs all use KST files as their font
definitions. KST format is as follows:
.nf
Word 0/ 1KSTID0
Word 1/ 9 bits 1COLUMN POSITION ADJUSTMENT0, 9 bits 1BASE LINE,,HEIGHT0
.ad
The remainder of the file has one block of data for each character. Each block
looks like:
.in 16
.un 8
1USER ID0 ;not currently used but low order bit is on. This
bit can be used to find the beginning of a new block. The last block is followed by a -1.
.nf
.in 0
1LEFT KERN,,CHARACTER CODE
RASTER WIDTH,,CHARACTER WIDTH
CHARACTER MATRIX0
.ad
The character matrix is stored four 8-bit bytes per word,
so that ILDBs with 8-bit byte size get successive bytes.
The remaining two low order bits are 0.
The bits are reversed in each byte (becuase of the way the XGP interface works)
so that the high order (leftmost) bit of the character is the
low order bit of the byte. The matrix is stored row by row. Each row starts
at a word boundary.
.sp
Some old MIT KST files, and all CMU's KST
files do not use the RASTER WIDTH variable. (All characters have
RASTER WIDTH=CHARACTER WIDTH.) The third word of those files has 0 in the
left half.
Programs which directly examine KST files for RASTER WIDTH should therefore,
if RASTER WIDTH=0, use CHARACTER WIDTH instead.
(Note that this also means that while MITAI can use CMU's KST files,
CMU cannot use MITAI KST files.)
Since when RASTER WIDTH=0, MITAI programs substitute CHARACTER WIDTH,
you should not write a program which will set RASTER WIDTH to zero.
When FED finds a character with zero RASTER WIDTH, FED will write
the character with RASTER WIDTH=1. This does not waste any space in
the XGP's PDP11, since the PDP11 does a vertical compaction of rasters,
eliminating top and bottom blank lines.
.he2
Odds and End
.pa
.sect
Odds and End
.sp
The KST, FNT, XH, and FED internal formats are
listed in the extravagantly commented FED source file (stored on the SYSENG directory).
FED also has extensive comments on programming the PDP10 to PDP11
interface. FED was written by Pitts Jarvis, with additions
by Joe Cohen.
Brian Harvey is responsible for SAIL font hackery, whose specifications
and fonts we copied.
.sp
Fonts are stored on the FONTS; directory, and are described in
Working Paper #72, XGP Font Catalog, by Tom Knight.
.sp
The source file for this memo is 1WP;FED 78Wn0, where n is the revision number.
.sp
.ce
THE END