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"FTXT" IFF Formatted Text
Date: November 15, 1985
From: Steve Shaw and Jerry Morrison, Electronic Arts and
Bob "Kodiak" Burns, Commodore-Amiga
Status: Draft 2.6
DRAFT DRAFT DRAFT
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1. Introduction
This memo is the IFF supplement for FORM FTXT. An FTXT is an IFF "data
section" or "FORM type" which can be an IFF file or a part of one containing
a stream of text plus optional formatting information."EA IFF 85"
is Electronic Arts' standard for interchange format files. (See the
IFF reference.)
An FTXT is an archival and interchange representation designed for
three uses. The simplest use is for a "console device" or "glass teletype"
(the minimal 2-D text layout means): a stream of "graphic" ("printable")
characters plus positioning characters "space" ("SP") and line terminator
("LF"). This is not intended for cursor movements on a screen although
it does not conflict with standard cursor-moving characters. The second
use is text that has explicit formatting information (or "looks")
such as font family and size, typeface, etc. The third use is as the
lowest layer of a structured document that also has "inherited" styles
to implicitly control character looks. For that use, FORMs FTXT would
be embedded within a future document FORM type. The beauty of FTXT
is that these three uses are interchangeable, that is, a program written
for one purpose can read and write the others' files. So a word processor
does not have to write a separate plain text file to communicate with
other programs.
Text is stored in one or more "CHRS" chunks inside an FTXT. Each CHRS
contains a stream of 8-bit text compatible with ISO and ANSI data
interchange standards. FTXT uses just the central character set from
the ISO/ANSI standards. (These two standards are henceforth called
"ISO/ANSI" as in "see the ISO/ANSI reference".)
Since it's possible to extract just the text portions from future
document FORM types, programs can exchange data without having to
save both plain text and formatted text representations.
Character looks are stored as embedded control sequences within CHRS
chunks. This document specifies which class of control sequences to
use: the CSI group. This document does not yet specify their meanings,
e.g. which one means "turn on italic face". Consult ISO/ANSI.
Section 2 defines the chunk types character stream "CHRS" and font
specifier "FONS". These are the "standard" chunks. Specialized chunks
for private or future needs can be added later. Section 3 outlines
an FTXT reader program that strips a document down to plain unformatted
text. Appendix A is a code table for the 8-bit ISO/ANSI character
set used here. Appendix B is an example FTXT shown as a box diagram.
Appendix C is a racetrack diagram of the syntax of ISO/ANSI control
sequences.
Reference:
Amiga[tm] is a trademark of Commodore-Amiga, Inc.
Electronic Arts[tm] is a trademark of Electronic Arts.
IFF: "EA IFF 85" Standard for Interchange Format Files describes the
underlying conventions for all IFF files.
ISO/ANSI: ISO/DIS 6429.2 and ANSI X3.64-1979. International Organization
for Standardization (ISO) and American National Standards Institute
(ANSI) data-interchange standards. The relevant parts of these two
standards documents are identical. ISO standard 2022 is also relevant.
2. Standard Data and Property Chunks
The main contents of a FORM FTXT is in its character stream "CHRS"
chunks. Formatting property chunks may also appear. The only formatting
property yet defined is "FONS", a font specifier. A FORM FTXT with
no CHRS represents an empty text stream. A FORM FTXT may contain nested
IFF FORMs, LISTs, or CATs, although a "stripping" reader (see section
3) will ignore them.
Character Set
FORM FTXT uses the core of the 8-bit character set defined by the
ISO/ANSI standards cited at the start of this document. (See Appendix
A for a character code table.) This character set is divided into
two "graphic" groups plus two "control" groups. Eight of the control
characters begin ISO/ANSI standard control sequences. (See "Control
Sequences", below.) Most control sequences and control characters
are reserved for future use and for compatibility with ISO/ANSI. Current
reader programs should skip them.
% C0 is the group of control characters in the range NUL (hex
0) through hex 1F. Of these, only LF (hex 0A) and ESC (hex 1B) are
significant. ESC begins a control sequence. LF is the line terminator,
meaning "go to the first horizontal position of the next line". All
other C0 characters are not used. In particular, CR (hex 0D) is not
recognized as a line terminator.
% G0 is the group of graphic characters in the range hex 20 through
hex 7F. SP (hex 20) is the space character. DEL (hex 7F) is the delete
character which is not used. The rest are the standard ASCII printable
characters "!" (hex 21) through "~" (hex 7E).
% C1 is the group of extended control characters in the range
hex 80 through hex 9F. Some of these begin control sequences. The
control sequence starting with CSI (hex 9B) is used for FTXT formatting.
All other control sequences and C1 control characters are unused.
% G1 is the group of extended graphic characters in the range
NBSP (hex A0) through "X" (hex FF). It is one of the alternate graphic
groups proposed for ISO/ANSI standardization.
Control Sequences
Eight of the control characters begin ISO/ANSI standard "control sequences"
(or "escape sequences"). These sequences are described below and diagrammed
in Appendix C.
G0 ::= (SP through DEL)
G1 ::= (NBSP through "X")
ESC-Seq ::= ESC (SP through "/")* ("0" through "~")
ShiftToG2 ::= SS2 G0
ShiftToG3 ::= SS3 G0
CSI-Seq ::= CSI (SP through "?")* ("@" through "~")
DCS-Seq ::= (DCS | OSC | PM | APC) (SP through "~" | G1)* ST
"ESC-Seq" is the control sequence ESC (hex 1B), followed by zero or
more characters in the range SP through "/S (hex 20 through hex 2F),
followed by a character in the range "0" through "~" (hex 30 through
hex 7E). These sequences are reserved for future use and should be
skipped by current FTXT reader programs.
SS2 (hex 8E) and SS3 (hex 8F) shift the single following G0 character
into yet-to-be-defined graphic sets G2 and G3, respectively. These
sequences should not be used until the character sets G2 and G3 are
standardized. A reader may simply skip the SS2 or SS3 (taking the
following character as a corresponding G0 character) or replace the
two-character sequence with a character like "?" to mean "absent".
FTXT uses "CSI-Seq" control sequences to store character formatting
(font selection by number, type face, and text size) and perhaps layout
information (position and rotation). "CSI-Seq" control sequences start
with CSI (the "control sequence introducer", hex 9B). Syntactically,
the sequence includes zero or more characters in the range SP through
"?" (hex 20 through hex 3F) and a concluding character in the range
"@" through "~" (hex 40 through hex 7E). These sequences may be skipped
by a minimal FTXT reader, i.e. one that ignores formatting information.
Note: A future FTXT standardization document will explain the uses
of CSI-Seq sequences for setting character face (light weight vs.
medium vs. bold, italic vs. upright, height, pitch, position, and
rotation). For now, consult the ISO/ANSI references.
"DCS-Seq" is the control sequences starting with DCS (hex 90), OSC
(hex 9D), PM (hex 9E), or APC (hex 9F), followed by zero or more characters
each of which is in the range SP through "~" (hex 20 through hex 7E)
or else a G1 character, and terminated by an ST (hex 9C). These sequences
are reserved for future use and should be skipped by current FTXT
reader programs.
Data Chunk CHRS
A CHRS chunk contains a sequence of 8-bit characters abiding by the
ISO/ANSI standards cited at the start of this document. This includes
the character set and control sequences as described above and summarized
in Appendicies A and C.
A FORM FTXT may contain any number of CHRS chunks. Taken together,
they represent a single stream of textual information. That is, the
contents of CHRS chunks are effectively concatenated except that (1)
each control sequence must be completely within a single CHRS chunk,
and (2) any formatting property chunks appearing between two CHRS
chunks affects the formatting of the latter chunk's text. Any formatting
settings set by control sequences inside a CHRS carry over to the
next CHRS in the same FORM FTXT. All formatting properties stop at
the end of the FORM since IFF specifies that adjacent FORMs are independent
of each other (although not independent of any properties inherited
from an enclosing LIST or FORM).
Property Chunk FONS
The optional property "FONS" holds a FontSpecifier as defined in the
C declaration below. It assignes a font to a numbered "font register"
so it can be referenced by number within subsequent CHRS chunks. (This
function is not provided within the ISO and ANSI standards.) The font
specifier gives both a name and a description for the font so the
recipient program can do font substitution.
By default, CHRS text uses font 1 until it selects another font. A
minimal text reader always uses font 1. If font 1 hasn't been specified,
the reader may use the local system font as font 1.
typedef struct {
UBYTE id;
/* 0 through 9 is a font id number referenced by an
* SGR control sequence selective parameter of 10
* through 19. Other values are reserved for future
* standardization.
*/
UBYTE pad1; /* reserved for future use; store 0 here */
UBYTE proportional;
/* proportional font? 0 = unknown, 1 = no, 2 = yes */
UBYTE serif;
/* serif font? 0 = unknown, 1 = no, 2 = yes */
char name[];
/* A NULL-terminated string naming preferred font. */
} FontSpecifier;
Fields are filed in the order shown. The UBYTE fields are byte-packed
(2 per 16-bit word). The field pad1 is reserved for future standardization.
Programs should store 0 there for now.
The field proportional indicates if the desired font is proportional
width as opposed to fixed width. The field serif indicates if the
desired font is serif as opposed to sans serif. [Issue: Discuss font
substitution!]
Future Properties
New optional property chunks may be defined in the future to store
additional formatting information. They will be used to represent
formatting not encoded in standard ISO/ANSI control sequences and
for "inherited" formatting in structured documents. Text orientation
might be one example.
Positioning Units
Unless otherwise specified, position and size units used in FTXT formatting
properties and control sequences are in decipoints (720 decipoints/inch).
This is ANSI/ISO Positioning Unit Mode (PUM) 2. While a metric standard
might be nice, decipoints allow the existing U.S.A. typographic units
to be encoded easily, e.g. "12 points" is "120 decipoints".
3. FTXT Stripper
An FTXT reader program can read the text and ignore all formatting
and structural information in a document FORM that uses FORMs FTXT
for the leaf nodes. This amounts to stripping a document down to a
stream of plain text. It would do this by skipping over all chunks
except FTXT.CHRS (CHRS chunks found inside a FORM FTXT) and within
the FTXT.CHRS chunks skipping all control characters and control sequences.
(Appendix C diagrams this text scanner.) It may also read FTXT.FONS
chunks to find a description for font 1.
Here's a Pascal-ish program for an FTXT stripper. Given a FORM (a
document of some kind), it scans for all FTXT.CHRS chunks. This would
likely be applied to the first FORM in an IFF file.
PROCEDURE ReadFORM4CHRS(); {Read an IFF FORM for FTXT.CHRS chunks.}
BEGIN
IF the FORM's subtype = "FTXT"
THEN ReadFTXT4CHRS()
ELSE WHILE something left to read in the FORM DO BEGIN
read the next chunk header;
CASE the chunk's ID OF
"LIST", "CAT ": ReadCAT4CHRS();
"FORM": ReadFORM4CHRS();
OTHERWISE skip the chunk's body;
END
END
END;
{Read a LIST or CAT for all FTXT.CHRS chunks.}
PROCEDURE ReadCAT4CHRS();
BEGIN
WHILE something left to read in the LIST or CAT DO BEGIN
read the next chunk header;
CASE the chunk's ID OF
"LIST", "CAT ": ReadCAT4CHRS();
"FORM": ReadFORM4CHRS();
"PROP": IF we're reading a LIST AND the PROP's subtype =
"FTXT"
THEN read the PROP for "FONS" chunks;
OTHERWISE error--malformed IFF file;
END
END
END;
PROCEDURE ReadFTXT4CHRS(); {Read a FORM FTXT for CHRS chunks.}
BEGIN
WHILE something left to read in the FORM FTXT DO BEGIN
read the next chunk header;
CASE the chunk's ID OF
"CHRS": ReadCHRS();
"FONS": BEGIN
read the chunk's contents into a FontSpecifier variable;
IF the font specifier's id = 1 THEN use this font;
END;
OTHERWISE skip the chunk's body;
END
END
END;
{Read an FTXT.CHRS. Skip all control sequences and unused control
chars.}
PROCEDURE ReadCHRS();
BEGIN
WHILE something left to read in the CHRS chunk DO
CASE read the next character OF
LF: start a new output line;
ESC: SkipControl([' '..'/'], ['0'..'~']);
IN [' '..'~'], IN [NBSP..'X']: output the character;
SS2, SS3: ; {Just handle the following G0 character
directly, ignoring the shift to G2 or G3.}
CSI: SkipControl([' '..'?'], ['@'..'~']);
DCS, OSC, PM, APC: SkipControl([' '..'~'] + [NBSP..'X'], [ST]);
END
END;
{Skip a control sequence of the format (rSet)* (tSet), i.e. any number
of characters in the set rSet followed by a character in the set tSet.}
PROCEDURE SkipControl(rSet, tSet);
VAR c: CHAR;
BEGIN
REPEAT c := read the next character
UNTIL c NOT IN rSet;
IF c NOT IN tSet
THEN put character c back into the input stream;
END
The following program is an optimized version of the above routines
ReadFORM4CHRS and ReadCAT4CHRS for the case where you're ignoring
fonts as well as formatting. It takes advantage of certain facts of
the IFF format to read a document FORM and its nested FORMs, LISTs,
and CATs without a stack. In other words, it's a hack that ignores
all fonts and faces to cheaply get to the plain text of the document.
{Cheap scan of an IFF FORM for FTXT.CHRS chunks.}
PROCEDURE ScanFORM4CHRS();
BEGIN
IF the document FORM's subtype = "FTXT"
THEN ReadFTXT4CHRS()
ELSE WHILE something left to read in the FORM DO BEGIN
read the next chunk header;
IF it's a group chunk (LIST, FORM, PROP, or CAT)
THEN read its subtype ID;
CASE the chunk's ID OF
"LIST", "CAT ":; {NOTE: See explanation below.*}
"FORM": IF this FORM's subtype = "FTXT" THEN
ReadFTXT4CHRS()
ELSE; {NOTE: See explanation below.*}
OTHERWISE skip the chunk's body;
END
END
END;