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ABOUT_ENCODINGS
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1991-06-09
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About the encoding files in this directory
==========================================
File format
-----------
The file format is compatible with PostScript syntax. It is also easy for
other programs to read. Do not change the format of the files, as programs
other than yours may need to read them.
Character codes that are not defined within the file default to their
values in Adobe StandardEncoding. Most PostScript interpreters cannot
handle more than 500 objects on their stack at once. So, allowing for a
few stack levels being used for other things, if you attempt to define more
than 240 or so entries in the file you will likely get a "stackoverflow"
error from your PostScript engine.
The file format is also compatible with that used by PPage in its PostScript
prologue. So it is easy to edit the prologue to change the encoding; just
delete the contents of "amigavec" right near the beginning of file and
insert in its place the contents of your chosen encoding file.
N.B. in PostScript the character "%" denotes the beginning of a comment; the
rest of the line is ignored. Numbers in the format "8#nnn" are octal; it is
quite OK to replace them with decimal values.
If you don't know what is in the Adobe standard encoding, just run "mkatc"
with a null encoding file and the verify option and it will tell you. If
you redirect the standard output you can use it to build encoding files.
IsoLatin1
---------
This is the standard Adobe ISOLatin1Encoding. This is essentially the
same as the Amiga character set. There are however possibly some very
slight differences, in that the character "hyphen" is preferred instead
of "minus", "quoteleft" instead of "grave", and "quoteright" instead of
"quotesingle". The various Amiga bitmaped fonts differ in their rendering
of these characters; I have prefered the Adobe interpretation as it is more
suitable for DTP, and is compatible with PPage. At screen resolutions, the
difference is usually immaterial.
All the ISO Latin 1 characters are present in standard Adobe PostScript
fonts. Most are also in the Compugraphic fonts, but some seem to be
missing: "twosuperior", "threesuperior", "onesuperior", "onequarter",
"onehalf", "threequarters", "Eth", "Yacute", "Thorn", "eth", "yacute",
"thorn". Also missing are "brokenbar", "minus" and "multiply", but these
have lookalikes.
PPageOrg
--------
This is the original character set used by Professional Page V2.0. It was
obtained by reverse engineering the Compugraphic fonts encoding files. It
is nearly a subset of the ISOLatin1 encoding, but with a few characters
replaced by near lookalikes. The characters "greater" and "less" have been
changed to "guilsinglright" and "guilsinglleft", which are more useful
typographically but not so good if you are typesetting program source code.
N.B. a comprehensive set of mathematical symbols is available in the
"Symbol" font, so you can always switch to it if a character you need is
not present in the standard encoding. You might even be able to make the
switch automatic using the Article Editor's translation facility.
NN.B. If you want double quotes, just type two single quotes and turn
kerning on. (Yes, I know it is obvious, but it took me a long time to
think of it.)
PPageExt
--------
This is an extension of the PPage character set. It is almost a superset,
except for the odd lookalike, and is fully upwards compatible. A number of
character codes were unused in the original set; instead of the missing
ISOLatin1 characters I have added the most useful typographic symbols
present in the Compugraphic and Adobe PostScript fonts. So now you can use
daggers, ellipses, ligatures, dashes etc. from within PPage.
N.B. I have reassigned "dieresis" from the original set; as it was not in any
of the keymaps and is not much use on its own anyway, it is unlikely that
anyone was using it. I have also replaced "macron" by "minus", an
approximate lookalike, and "ring" by "degree" as per ISO Latin 1.
N.N.B. You can make your own fractions by using the "fraction" character and
adjusting the size and baseline of the digits. You can also do subscripts
and superscripts.
PPageExtOSF
-----------
This is a variation on PPageExt, with the figures replaced by old style
(non-lining) figures. This may be useful if you have a font that includes
these characters.
Windows
-------
MS Windows uses a character set that is identical to ISO Latin 1, but with
a few additional characters. It is therefore a superset of the Amiga
character set. I have included it because it might be a suitable base for
defining an extended character set for the Amiga.
N.B. the additional characters are in the range Hex 80 - 9F. These are
offically designated as "control" characters. Many Amiga programs (including
PPage 2.0 and its Article Editor) cannot handle these character codes.
Acents
------
Standard Adobe level 1 PostScript interpreters (in other words most
PostScript printers) require all the components of the composite characters
to be present in the encoding somewhere before they can be rendered. So
for example to render "icircumflex" the characters "dotlessi" and
"circumflex" must be present in the encoding, even though they are not
actually referenced directly.
It is convenient to assign to the accents codes that are control characters,
and therefore are not going to be needed for real data characters. So the
accents are defined in a separate encoding file, using characters in the
range Hex 00 - 1F. If you are creating a PostScript encoding vector for
downloading to a printer you should include this file as well as the
encoding of your choice. But if you are just generating bitmaps or metrics,
or Compugraphic encodings then the accents can be ignored.
N.B. Post does not require the accents to be present, nor does Adobe
PostScript level 2.
Differences
-----------
I have tabulated here the differences between the encoding vectors, giving
also the keystrokes in the usa1 keymap.
Key ISOLatin1 PPageExt PpageOrg
--- --------- -------- --------
45 - minus hyphen hyphen
60 < less guilsinglleft guilsinglleft
62 > greater guilsinglright guilsinglright
160 space space space
166 Alt/I brokenbar fraction
168 ??? dieresis trademark
173 Alt/n hyphen hyphen
175 Alt/N macron minus
176 Alt/w degree degree ring
177 Alt/z plusminus plusminus
178 Alt/2 twosuperior fi
179 Alt/3 threesuperior fl
180 ??? acute quotesingle
181 Alt/u mu mu
183 Alt/8 periodcentered bullet bullet
184 Alt/m cedilla quotesinglbase quotesinglbase
185 Alt/1 onesuperior florin
188 Alt/5 onequarter quotedblleft
189 Alt/6 onehalf quotedblright
190 Alt/7 threequaters quotedblbase
208 Alt/D Eth emdash
215 Alt/x multiply multiply
221 Alt/f Y Yacute ellipsis
222 Alt/T Thorn daggerdbl
240 Alt/d eth endash
247 Alt/X divide divide
253 Alt/f y yacute perthousand
254 Alt/t thorn dagger