Cream of the Crop 25/Cream of the Crop 25.iso/utility/ffe101.zip/SOUND.SWG/0013_IFF EXPLANATION.pas

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"EA IFF 85" Standard for Interchange Format Files

Document Date:          January 14, 1985
From:                   Jerry Morrison, Electronic Arts
Status of Standard:     Released and in use

1. Introduction

Standards are Good for Software Developers

As  home computer hardware evolves to  better and better media machines,
the  demand  increases  for  higher  quality,  more  detailed data. Data
development  gets  more  expensive, requires  more  expertise and better
tools,  and has to be shared  across projects. Think about several ports
of a product on one CD-ROM with 500M Bytes of common data!

Development  tools  need  standard  interchange  file  formats.  Imagine
scanning  in  images of "player" shapes,  moving them to a paint program
for  editing,  then incorporating them into  a  game. Or writing a theme
song  with  a Macintosh score editor  and incorporating it into an Amiga
game.  The  data must at times  be transformed, clipped, filled out, and
moved  across machine kinds. Media projects will depend on data transfer
from graphic, music, sound effect, animation, and script tools.

Standards are Good for Software Users

Customers  should  be able to move  their own data between independently
developed  software  products.  And  they should  be  able  to  buy data
libraries usable across many such products. The types of data objects to
exchange are open-ended and include plain and formatted text, raster and
structured  graphics,  fonts, music,  sound  effects, musical instrument
descriptions, and animation.

The  problem with expedient file formats  typically memory dumps is that
they're too provincial. By designing data for one particular use (e.g. a
screen  snapshot), they preclude future expansion (would you like a full
page  picture?  a multi-page document?).  In  neglecting the possibility
that  other programs might read their data, they fail to save contextual
information (how many bit planes? what resolution?). Ignoring that other
programs  might  create  such files,  they're  intolerant  of extra data
(texture  palette for a picture editor), missing data (no color map), or
minor  variations  (smaller image). In  practice, a filed representation
should  rarely mirror an in-memory  representation. The former should be
designed  for  longevity; the latter to  optimize the manipulations of a
particular  program.  The  same filed data  will  be read into different
memory formats by different programs.

The IFF philosophy: "A little behind-the-scenes conversion when programs
read  and  write  files  is  far  better  than  NxM  explicit conversion
utilities for highly specialized formats."

So  we need some standardization  for data interchange among development
tools  and  products.  The more developers  that  adopt  a standard, the
better for all of us and our customers.

Here is "EA IFF 1985"

Here is our offering: Electronic Arts' IFF standard for Interchange File
Format.  The full name is "EA IFF 1985". Alternatives and justifications
are  included for certain choices. Public domain subroutine packages and
utility  programs  are  available  to  make  it  easy  to  write and use
IFF-compatible programs.

Part  1  introduces the standard. Part  2  presents its requirements and
background.  Parts  3, 4, and 5  define the primitive data types, FORMs,
and  LISTs, respectively, and how to define new high level types. Part 6
specifies the top level file structure. Appendix A is included for quick
reference  and  Appendix  B  names  the  committee  responsible for this
standard.

References

American  National Standard Additional Control Codes for Use with ASCII,
ANSI  standard  3.64-1979  for  an 8-bit  character  set.  See  also ISO
standard 2022 and ISO/DIS standard 6429.2.

Amiga[tm] is a trademark of Commodore-Amiga, Inc.

C,  A Reference Manual, Samuel P. Harbison and Guy L. Steele Jr., Tartan
Laboratories. Prentice-Hall, Englewood Cliffs, NJ, 1984.

Compiler  Construction, An Advanced Course, edited by F. L. Bauer and J.
Eickel  (Springer-Verlag,  1976). This book is  one  of many sources for
information on recursive descent parsing.

DIF  Technical  Specification (c)1981 by  Software Arts, Inc. DIF[tm] is
the  format for spreadsheet data interchange developed by Software Arts,
Inc. DIF[tm] is a trademark of Software Arts, Inc.

Electronic Arts[tm] is a trademark of Electronic Arts.

"FTXT" IFF Formatted Text, from Electronic Arts. IFF supplement document
for a text format.

Inside  Macintosh  (c)  1982, 1983, 1984,  1985  Apple Computer, Inc., a
programmer's   reference  manual.  Apple(R)  is  a  trademark  of  Apple
Computer,  Inc. Macintosh[tm] is a trademark licensed to Apple Computer,
Inc.

"ILBM"  IFF  Interleaved  Bitmap, from  Electronic  Arts. IFF supplement
document for a raster image format.

M68000  16/32-Bit Microprocessor Programmer's  Reference Manual(c) 1984,
1982, 1980, 1979 by Motorola, Inc.

PostScript   Language  Manual  (c)   1984  Adobe  Systems  Incorporated.
PostScript[tm]   is  a  trademark  of  Adobe  Systems,  Inc.  Times  and
Helvetica(R) are trademarks of Allied Corporation.

InterScript:  A Proposal for a Standard  for the Interchange of Editable
Documents  (c)1984  Xerox Corporation.  Introduction  to InterScript (c)
1985 Xerox Corporation.

2. Background for Designers

Part  2  is  about  the  background,  requirements,  and  goals  for the
standard.  It's  geared for people who want  to  design new types of IFF
objects.  People just interested in using  the standard may wish to skip
this part.

What Do We Need?

A  standard  should  be long on  prescription  and short on overhead. It
should  give  lots  of rules for  designing  programs and data files for
synergy.  But  neither the programs nor  the  files should cost too much
more  than  the expedient variety. While  we're looking to a future with
CD-ROMs  and  perpendicular  recording, the  standard  must work well on
floppy disks.

For  program portability, simplicity, and  efficiency, formats should be
designed  with more than one implementation style in mind. (In practice,
pure  stream  I/O is adequate although  random access makes it easier to
write  files.) It ought to be possible to  read one of many objects in a
file without scanning all the preceding data. Some programs need to read
and  play  out  their  data in real  time,  so  we need good compromises
between generality and efficiency.

As  much as we need standards, they  can't hold up product schedules. So
we  also  need a kind of  decentralized extensibility where any software
developer can define and refine new object types without some "standards
authority"  in  the  loop. Developers must  be  able  to extend existing
formats  in a forward- and backward-compatible way. A central repository
for  design  information  and  example programs  can  help  us take full
advantage of the standard.

For  convenience,  data formats should  heed the restrictions of various
processors  and  environments. E.g.  word-alignment  greatly helps 68000
access at insignificant cost to 8088 programs.

Other  goals include the ability to share common elements over a list of
objects  and the ability to construct composite objects containing other
data objects with structural information like directories.

And  finally, "Simple things should be  simple and complex things should
be possible." Alan Kay.

Think Ahead

Let's  think ahead and build programs that read and write files for each
other  and  for programs yet to be  designed. Build data formats to last
for future computers so long as the overhead is acceptable. This extends
the usefulness and life of today's programs and data.

To  maximize  interconnectivity,  the standard  file  structure  and the
specific  object formats must all be general and extensible. Think ahead
when  designing an object. It should  serve many purposes and allow many
programs  to  store  and read back  all  the information they need; even
squeeze  in custom data. Then a  programmer can store the available data
and  is  encouraged  to  include  fixed  contextual  details.  Recipient
programs  can  read the needed  parts,  skip unrecognized stuff, default
missing  data, and use the stored context  to help transform the data as
needed.

Scope

IFF  addresses  these needs by defining  a standard file structure, some
initial  data  object  types, ways to  define  new  types, and rules for
accessing  these  files.  We  can accomplish  a  great  deal  by writing
programs   according   to  this  standard,   but   don't  expect  direct
compatibility  with existing software. We'll need conversion programs to
bridge the gap from the old world.

IFF  is  geared for computers that  readily process information in 8-bit
bytes.  It  assumes a "physical layer"  of data storage and transmission
that  reliably maintains "files" as strings of 8-bit bytes. The standard
treats  a "file" as a container of  data bytes and is independent of how
to find a file and whether it has a byte count.

This  standard does not by itself  implement a clipboard for cutting and
pasting  data  between programs. A  clipboard  needs software to mediate
access,  to maintain a "contents version  number" so programs can detect
updates, and to manage the data in "virtual memory".

Data Abstraction

The  basic  problem  is  how to  represent  information  in a way that's
program-independent,  compiler-  independent,  machine-independent,  and
device-independent.

The  computer  science  approach is  "data  abstraction",  also known as
"objects", "actors", and "abstract data types". A data abstraction has a
"concrete   representation"   (its   storage   format),   an   "abstract
representation"  (its capabilities and uses), and access procedures that
isolate  all the calling software from the concrete representation. Only
the  access  procedures touch the  data  storage. Hiding mutable details
behind   an   interface  is  called   "information  hiding".  What  data
abstraction  does  is abstract from  details of implementing the object,
namely   the   selected  storage   representation   and  algorithms  for
manipulating it.

The  power  of  this  approach is  modularity.  By  adjusting the access
procedures  we can extend and restructure the data without impacting the
interface  or its callers. Conversely, we can extend and restructure the
interface  and callers without making existing data obsolete. It's great
for interchange!

But we seem to need the opposite: fixed file formats for all programs to
access.  Actually, we could file  data abstractions ("filed objects") by
storing the data and access procedures together. We'd have to encode the
access procedures in a standard machine-independent programming language
la  PostScript.  Even still, the interface  can't evolve freely since we
can't  update  all  copies of the  access  procedures.  So we'll have to
design our abstract representations for limited evolution and occasional
revolution (conversion).

In  any  case,  today's  microcomputers  can't  practically  store  data
abstractions.  They can do the next best thing: store arbitrary types of
data  in "data chunks", each with a  type identifier and a length count.
The type identifier is a reference by name to the access procedures (any
local  implementation).  The length  count  enables storage-level object
operations like "copy" and "skip to next" independent of object type.

Chunk  writing  is  straightforward. Chunk  reading  requires  a trivial
parser  to scan each chunk and  dispatch to the proper access/conversion
procedure. Reading chunks nested inside other chunks requires recursion,
but no lookahead or backup.

That's the main idea of IFF. There are, of course, a few other detailsI

Previous Work

Where our needs are similar, we borrow from existing standards.

Our  basic need to move data between independently developed programs is
similar  to  that  addressed  by  the  Apple  Macintosh  desk  scrap  or
"clipboard"  [Inside  Macintosh  chapter  "Scrap  Manager"].  The  Scrap
Manager  works  closely  with the Resource  Manager,  a  handy filer and
swapper  for  data  objects  (text  strings,  dialog  window  templates,
pictures,  fontsI) including types yet  to be designed [Inside Macintosh
chapter   "Resource  Manager"].  The  Resource   Manager  is  a  kin  to
Smalltalk's object swapper.

We  will  probably  write a Macintosh  desk  accessory that converts IFF
files to and from the Macintosh clipboard for quick and easy interchange
with programs like MacPaint and Resource Mover.

Macintosh  uses a simple and elegant scheme of 4-character "identifiers"
to identify resource types, clipboard format types, file types, and file
creator  programs.  Alternatives  are unique  ID  numbers  assigned by a
central  authority  or  by hierarchical  authorities,  unique ID numbers
generated  by  algorithm,  other  fixed  length  character  strings, and
variable length strings. Character string identifiers double as readable
signposts  in  data files and programs. The  choice of 4 characters is a
good  tradeoff between storage space, fetch/compare/store time, and name
space size. We'll honor Apple's designers by adopting this scheme.

"PICT"  is  a  good  example of  a  standard  structured graphics format
(including  raster  images) and its  many uses [Inside Macintosh chapter
"QuickDraw"].  Macintosh  provides QuickDraw routines  in ROM to create,
manipulate,  and  display  PICTs. Any application  can  create a PICT by
simply  asking QuickDraw to record a sequence of drawing commands. Since
it's  just  as easy to ask QuickDraw to  render  a PICT to a screen or a
printer,  it's very effective to pass them between programs, say from an
illustrator  to a word processor. An important feature is the ability to
store  "comments"  in a PICT which  QuickDraw  will ignore. Actually, it
passes them to your optional custom "comment handler".

PostScript,  Adobe's  print  file  standard, is  a  more  general way to
represent any print image (which is a specification for putting marks on
paper)   [PostScript   Language  Manual].  In   fact,  PostScript  is  a
full-fledged  programming language. To interpret a PostScript program is
to  render a document on a raster output device. The language is defined
in  layers: a lexical layer of  identifiers, constants, and operators; a
layer  of  reverse polish semantics including  scope  rules and a way to
define  new  subroutines;  and  a  printing-specific  layer  of built-in
identifiers  and operators for rendering graphic images. It is clearly a
powerful  (Turing  equivalent)  image definition  language.  PICT  and a
subset of PostScript are candidates for structured graphics standards.

A  PostScript  document  can  be printed  on  any  raster  output device
(including a display) but cannot generally be edited. That's because the
original  flexibility  and constraints have  been  discarded. Besides, a
PostScript  program  may use arbitrary  computation to supply parameters
like  placement  and  size  to  each  operator.  A  QuickDraw  PICT,  in
comparison,   is   a  more  restricted   format  of  graphic  primitives
parameterized  by constants. So a PICT can be edited at the level of the
primitives,  e.g.  move  or thicken a line.  It  cannot be edited at the
higher level of, say, the bar chart data which generated the picture.

PostScript has another limitation: Not all kinds of data amount to marks
on paper. A musical instrument description is one example. PostScript is
just not geared for such uses.

"DIF" is another example of data being stored in a general format usable
by  future  programs [DIF Technical Specification].  DIF is a format for
spreadsheet  data interchange. DIF and  PostScript are both expressed in
plain  ASCII  text  files. This is  very  handy for printing, debugging,
experimenting,  and transmitting across modems.  It can have substantial
cost in compaction and read/write work, depending on use. We won't store
IFF files this way but we could define an ASCII alternate representation
with a converter program.

InterScript  is  Xerox' standard for  interchange  of editable documents
[Introduction  to  InterScript]. It approaches  a harder problem: How to
represent  editable word processor documents  that may contain formatted
text,  pictures,  cross-references like figure  numbers, and even highly
specialized  objects  like mathematical  equations?  InterScript aims to
define  one  standard representation for  each kind of information. Each
InterScript-compatible  editor  is supposed to  preserve  the objects it
doesn't  understand  and  even maintain  nested  cross-references.  So a
simple  word  processor would let you edit  the text of a fancy document
without discarding the equations or disrupting the equation numbers.

Our  task  is similarly to store  high level information and preserve as
much  content as practical while moving it between programs. But we need
to  span a larger universe of data  types and cannot expect to centrally
define  them  all. Fortunately, we don't  need to make programs preserve
information  that  they  don't understand. And  for  better or worse, we
don't have to tackle general-purpose cross-references yet.


3. Primitive Data Types

Atomic components such as integers and characters that are interpretable
directly  by the CPU are specified in  one format for all processors. We
chose a format that's most convenient for the Motorola MC68000 processor
[M68000 16/32-Bit Microprocessor Programmer's Reference Manual].

N.B.:  Part  3 dictates the format  for "primitive" data types where and
only  where  used  in the overall  file  structure and standard kinds of
chunks (Cf. Chunks). The number of such occurrences will be small enough
that  the  costs  of conversion,  storage,  and management of processor-
specific  files  would far exceed the  costs of conversion during I/O by
"foreign"  programs.  A  particular data chunk  may  be specified with a
different  format for its internal primitive types or with processor- or
environment-  speci  fic variants if  necessary to optimize local usage.
Since  that hurts data interchange, it's not recommended. (Cf. Designing
New Data Sections, in Part 4.)

Alignment

All  data objects larger than a byte  are aligned on even byte addresses
relative  to the start of the file.  This may require padding. Pad bytes
are to be written as zeros, but don't count on that when reading.

This  means that every odd-length "chunk"  (see below) must be padded so
that  the  next  one will fall on  an  even boundary. Also, designers of
structures to be stored in chunks should include pad fields where needed
to  align every field larger than a  byte. Zeros should be stored in all
the pad bytes.

Justification:  Even-alignment causes a little extra work for files that
are  used  only  on  certain processors  but  allows  68000  programs to
construct  and scan the data in memory and do block I/O. You just add an
occasional  pad  field  to data structures  that  you're  going to block
read/write  or else stream read/write an extra byte. And the same source
code  works on all processors. Unspecified alignment, on the other hand,
would  force 68000 programs to (dis)assemble word and long-word data one
byte  at a time. Pretty cumbersome in  a high level language. And if you
don't  conditionally  compile that out  for  other processors, you won't
gain anything.

Numbers

Numeric  types  supported  are two's  complement  binary integers in the
format  used  by the MC68000 processor  high byte first, high word first
the  reverse  of  8088 and 6502  format.  They could potentially include
signed  and  unsigned 8, 16, and 32  bit  integers but the standard only
uses the following:

UBYTE 8 bits
unsigned WORD 16 bits
signed UWORD 16 bits
unsigned LONG 32 bits signed

The  actual type definitions depend on the CPU and the compiler. In this
document,  we'll  express  data type  definitions  in  the C programming
language. [See C, A Reference Manual.] In 68000 Lattice C:

typedef unsigned char   UBYTE;  /*  8 bits unsigned     */
typedef short   WORD;   /* 16 bits signed       */
typedef unsigned short  UWORD;  /* 16 bits unsigned     */
typedef long    LONG;   /* 32 bits signed       */

Characters

The  following  character set is  assumed  wherever characters are used,
e.g. in text strings, IDs, and TEXT chunks (see below).

Characters  are encoded in 8-bit ASCII. Characters in the range NUL (hex
0)  through  DEL (hex 7F) are well  defined by the 7-bit ASCII standard.
IFF uses the graphic group RJS (SP, hex 20) through R~S (hex 7E).

Most  of  the  control  character group hex  01  through  hex 1F have no
standard meaning in IFF. The control character LF (hex 0A) is defined as
a  "newline" character. It denotes an intentional line break, that is, a
paragraph  or  line terminator. (There is  no  way to store an automatic
line  break.  That  is  strictly  a  function  of  the  margins  in  the
environment the text is placed.) The control character ESC (hex 1B) is a
reserved  escape  character under the  rules  of ANSI standard 3.64-1979
American  National Standard Additional Control Codes for Use with ASCII,
ISO standard 2022, and ISO/DIS standard 6429.2.

Characters  in the range hex 7F through  hex FF are not globally defined
in IFF. They are best left reserved for future standardization. But note
that  the  FORM type FTXT (formatted  text) defines the meaning of these
characters  within  FTXT forms. In  particular,  character values hex 7F
through  hex 9F are control codes while characters hex A0 through hex FF
are extended graphic characters like , as per the ISO and ANSI standards
cited above. [See the supplementary document "FTXT" IFF Formatted Text.]

Dates

A "creation date" is defined as the date and time a stream of data bytes
was  created.  (Some systems call this  a "last modified date".) Editing
some  data changes its creation date. Moving the data between volumes or
machines does not.

The  IFF  standard  date  format will be  one  of  those used in MS-DOS,
Macintosh,  or  Amiga DOS (probably a  32-bit unsigned number of seconds
since a reference point). Issue: Investigate these three.

Type IDs

A  "type ID", "property name", "FORM  type", or any other IFF identifier
is  a  32-bit value: the concatenation  of  four ASCII characters in the
range  R S (SP, hex 20) through R~S (hex 7E). Spaces (hex 20) should not
precede  printing characters; trailing spaces are ok. Control characters
are forbidden.

typedef CHAR ID[4];

IDs are compared using a simple 32-bit case-dependent equality test.

Data  section  type  IDs (aka FORM  types)  are restriced IDs. (Cf. Data
Sections.)  Since they may be stored  in filename extensions (Cf. Single
Purpose  Files) lower case letters  and punctuation marks are forbidden.
Trailing spaces are ok.

Carefully choose those four characters when you pick a new ID. Make them
mnemonic  so  programmers  can look at  an  interchange  format file and
figure  out  what  kind  of data it  contains.  The  name space makes it
possible for developers scattered around the globe to generate ID values
with  minimal  collisions  so long as  they  choose  specific names like
"MUS4"  instead  of  general  ones  like  "TYPE"  and  "FILE".  EA  will
"register" new FORM type IDs and format descriptions as they're devised,
but  collisions will be improbable so there  will be no pressure on this
"clearinghouse" process. Appendix A has a list of currently defined IDs.

Sometimes  it's  necessary  to  make  data  format  changes  that aren't
backward  compatible. Since IDs are used  to denote data formats in IFF,
new  IDs are chosen to denote revised formats. Since programs won't read
chunks  whose IDs they don't recognize  (see Chunks, below), the new IDs
keep  old programs from stumbling over new data. The conventional way to
chose a "revision" ID is to increment the last character if it's a digit
or  else  change  the last character to  a  digit. E.g. first and second
revisions  of the ID "XY" would be  "XY1" and "XY2". Revisions of "CMAP"
would be "CMA1" and "CMA2".

Chunks

Chunks  are the building blocks in the IFF structure. The form expressed
as a C typedef is:

typedef struct {
        ID      ckID;
        LONG    ckSize; /* sizeof(ckData) */
        UBYTE   ckData[/* ckSize */];
        } Chunk;

We  can diagram an example chunk a "CMAP" chunk containing 12 data bytes
like this:
                        ----------------
                ckID:   |    'CMAP'    |
                ckSize: |      12      |
                ckData: | 0, 0, 0, 32  |   --------
                        | 0, 0, 64, 0  |    12 bytes
                        | 0, 0, 64, 0  |   ---------
                        ----------------

The  fixed header part means "Here's a type ckID chunk with ckSize bytes
of data."

The  ckID  identifies the format and purpose  of the chunk. As a rule, a
program must recognize ckID to interpret ckData. It should skip over all
unrecognized  chunks. The ckID also serves as a format version number as
long as we pick new IDs to identify new formats of ckData (see above).

The  following  ckIDs are universally  reserved  to identify chunks with
particular  IFF  meanings: "LIST", "FORM", "PROP",  "CAT ", and " ". The
special ID " " (4 spaces) is a ckID for "filler" chunks, that is, chunks
that  fill space but have no meaningful contents. The IDs "LIS1" through
"LIS9",  "FOR1"  through "FOR9", and  "CAT1" through "CAT9" are reserved
for future "version number" variations. All IFF-compatible software must
account for these 23 chunk IDs. Appendix A has a list of predefined IDs.

The ckSize is a logical block size how many data bytes are in ckData. If
ckData is an odd number of bytes long, a 0 pad byte follows which is not
included  in  ckSize. (Cf. Alignment.) A  chunk's total physical size is
ckSize  rounded up to an even number plus the size of the header. So the
smallest  chunk  is  8  bytes  long with  ckSize  =  0.  For the sake of
following  chunks,  programs  must  respect  every  chunk's  ckSize as a
virtual  end-of-file  for  reading  its  ckData  even  if  that  data is
malformed, e.g. if nested contents are truncated.

We  can describe the syntax of a  chunk as a regular expression with "#"
representing  the  ckSize,  i.e. the  length  of  the following {braced}
bytes.  The  "[0]" represents a sometimes  needed pad byte. (The regular
expressions  in this document are collected  in Appendix A along with an
explanation of notation.)

Chunk   ::= ID #{ UBYTE* } [0]

One  chunk  output technique is to  stream  write a chunk header, stream
write  the chunk contents, then random access back to the header to fill
in  the  size. Another technique is to  make a preliminary pass over the
data to compute the size, then write it out all at once.

Strings, String Chunks, and String Properties

In  a string of ASCII text, LF denotes a forced line break (paragraph or
line   terminator).   Other  control  characters   are  not  used.  (Cf.
Characters.)

The  ckID for a chunk that contains  a string of plain, unformatted text
is  "TEXT". As a practical matter, a  text string should probably not be
longer than 32767 bytes. The standard allows up to 231 - 1 bytes.

When  used as a data property (see below),  a text string chunk may be 0
to 255 characters long. Such a string is readily converted to a C string
or  a  Pascal STRING[255]. The ckID of  a  property must be the property
name, not "TEXT".

When  used  as a part of a  chunk  or data property, restricted C string
format  is  normally used. That means 0  to 255 characters followed by a
NUL byte (ASCII value 0).

Data Properties

Data  properties specify attributes for following (non-property) chunks.
A data property essentially says "identifier = value", for example "XY =
(10,  200)",  telling something about  following  chunks. Properties may
only  appear inside data sections ("FORM" chunks, cf. Data Sections) and
property sections ("PROP" chunks, cf. Group PROP).

The  form  of a data property is a  special case of Chunk. The ckID is a
property  name  as well as a property  type.  The ckSize should be small
since data properties are intended to be accumulated in RAM when reading
a file. (256 bytes is a reasonable upper bound.) Syntactically:

Property::= Chunk

When  designing  a  data  object,  use  properties  to  describe context
information  like the size of an image,  even if they don't vary in your
program. Other programs will need this information.

Think  of property settings as assignments to variables in a programming
language.  Multiple  assignments  are  redundant  and  local assignments
temporarily  override  global  assignments.  The  order  of  assignments
doesn't  matter as long as they precede the affected chunks. (Cf. LISTs,
CATs, and Shared Properties.)

Each  object  type (FORM type) is a  local  name space for property IDs.
Think  of  a  "CMAP"  property  in a  "FORM  ILBM"  as  the qualified ID
"ILBM.CMAP". Property IDs specified when an object type is designed (and
therefore  known to all clients) are called "standard" while specialized
ones added later are "nonstandard".

Links

Issue:  A  standard mechanism for "links"  or "cross references" is very
desirable  for things like combining  images and sounds into animations.
Perhaps  we'll  define  "link" chunks within  FORMs  that refer to other
FORMs  or to specific chunks within the same and other FORMs. This needs
further work. EA IFF 1985 has no standard link mechanism.

For now, it may suffice to read a list of, say, musical instruments, and
then just refer to them within a musical score by index number.

File References

Issue:  We  may  need a standard form  for  references to other files. A
"file  ref"  could  name  a directory and  a  file  in  the same type of
operating  system as the ref's originator. Following the reference would
expect  the file to be on some mounted volume. In a network environment,
a file ref could name a server, too.

Issue: How can we express operating-system independent file refs?

Issue:  What about a means to reference a portion of another file? Would
this  be  a  "file ref" plus a  reference  to a "link" within the target
file?

4. Data Sections

The  first thing we need of a file is to check: Does it contain IFF data
and,  if  so, does it contain the kind  of data we're looking for? So we
come to the notion of a "data section".

A  "data section" or IFF "FORM" is one self-contained "data object" that
might  be  stored in a file by itself.  It is one high level data object
such  as a picture or a sound  effect. The IFF structure "FORM" makes it
self-  identifying. It could be a  composite object like a musical score
with nested musical instrument descriptions.

Group FORM

A data section is a chunk with ckID "FORM" and this arrangement:

FORM  ::=  "FORM"  #{  FormType  (LocalChunk |  FORM  |  LIST  | CAT)* }
FormType::= ID LocalChunk ::= Property | Chunk

The  ID  "FORM"  is a syntactic keyword  like  "struct" in C. Think of a
"struct  ILBM" containing a field "CMAP".  If you see "FORM" you'll know
to  expect  a FORM type ID (the  structure name, "ILBM" in this example)
and  a particular contents arrangement or "syntax" (local chunks, FORMs,
LISTs,  and  CATs). (LISTs and CATs are  discussed  in part 5, below.) A
"FORM  ILBM",  in  particular, might contain  a  local  chunk "CMAP", an
"ILBM.CMAP" (to use a qualified name).

So  the  chunk ID "FORM" indicates a  data  section. It implies that the
chunk  contains  an  ID and some number  of  nested chunks. In reading a
FORM,  like  any  other  chunk, programs  must  respect  its ckSize as a
virtual end-of-file for reading its contents, even if they're truncated.

The  FormType  (or  FORM type) is a  restricted  ID that may not contain
lower  case letters or punctuation characters. (Cf. Type IDs. Cf. Single
Purpose Files.)

The  type-specific  information  in  a FORM  is  composed  of its "local
chunks":  data  properties and other chunks.  Each  FORM type is a local
name  space  for local chunk IDs. So  "CMAP"  local chunks in other FORM
types  may  be unrelated to "ILBM.CMAP".  More than that, each FORM type
defines  semantic  scope. If you know what  a  FORM ILBM is, you'll know
what an ILBM.CMAP is.

Local chunks defined when the FORM type is designed (and therefore known
to  all  clients of this type)  are  called "standard" while specialized
ones added later are "nonstandard".

Among  the  local  chunks,  property  chunks  give  settings for various
details  like  text  font while the  other  chunks  supply the essential
information.  This  distinction  is not  clear  cut.  A property setting
cancelled  by  a later setting of the  same  property has effect only on
data chunks in between. E.g. in the sequence:

prop1 = x  (propN = value)*  prop1 = y

where the propNs are not prop1, the setting prop1 = x has no effect.

The  following universal chunk IDs are reserved inside any FORM: "LIST",
"FORM",  "PROP",  "CAT ", "JJJJ",  "LIS1" through "LIS9", "FOR1" through
"FOR9",  and  "CAT1"  through "CAT9". (Cf.  Chunks.  Cf. Group LIST. Cf.
Group  PROP.)  For clarity, these universal  chunk names may not be FORM
type IDs, either.

Part  5, below, talks about grouping FORMs into LISTs and CATs. They let
you  group  a bunch of FORMs but  don't impose any particular meaning or
constraints on the grouping. Read on.

Composite FORMs

A  FORM  chunk inside a FORM is  a full-fledged data section. This means
you  can build a composite object  like a multi-frame animation sequence
from  available  picture  FORMs and sound  effect  FORMs. You can insert
additional chunks with information like frame rate and frame count.

Using composite FORMs, you leverage on existing programs that create and
edit  the  component  FORMs.  Those  editors  may  even  look  into your
composite  object  to copy out its  type of component, although it'll be
the  rare  program that's fancy enough to  do that. Such editors are not
allowed to replace their component objects within your composite object.
That's   because   the  IFF  standard   lets   you  specify  consistency
requirements  for  the composite FORM such  as  maintaining a count or a
directory  of  the components. Only programs  that are written to uphold
the rules of your FORM type should create or modify such FORMs.

Therefore,  in  designing a program  that creates composite objects, you
are  strongly  requested to provide a  facility for your users to import
and  export  the  nested FORMs. Import  and  export  could move the data
through a clipboard or a file.

Here are several existing FORM types and rules for defining new ones.

FTXT

An FTXT data section contains text with character formatting information
like  fonts  and  faces.  It has  no  paragraph  or  document formatting
information  like margins and page headers. FORM FTXT is well matched to
the  text  representation  in  Amiga's  Intuition  environment.  See the
supplemental document "FTXT" IFF Formatted Text.

ILBM

"ILBM"   is   an   InterLeaved   BitMap   image   with   color   map;  a
machine-independent  format for raster images. FORM ILBM is the standard
image  file  format  for the Commodore-Amiga  computer  and is useful in
other  environments,  too.  See  the  supplemental  document  "ILBM" IFF
Interleaved Bitmap.

PICS

The  data  chunk inside a "PICS" data  section has ID "PICT" and holds a
QuickDraw picture. Issue: Allow more than one PICT in a PICS? See Inside
Macintosh chapter "QuickDraw" for details on PICTs and how to create and
display them on the Macintosh computer.

The  only standard property for PICS  is "XY", an optional property that
indicates  the  position of the PICT  relative to "the big picture". The
contents of an XY is a QuickDraw Point.

Note:  PICT  may be limited to Macintosh  use, in which case there'll be
another format for structured graphics in other environments.

Other Macintosh Resource Types

Some  other Macintosh resource types could be adopted for use within IFF
files; perhaps MWRT, ICN, ICN#, and STR#.

Issue: Consider the candidates and reserve some more IDs.

Designing New Data Sections

Supplemental documents will define additional object types. A supplement
needs  to  specify the object's purpose, its  FORM  type ID, the IDs and
formats   of  standard  local  chunks,  and  rules  for  generating  and
interpreting  the  data.  It's  a good  idea  to  supply typedefs and an
example  source  program  that accesses the  new  object. See "ILBM" IFF
Interleaved Bitmap for a good example.

Anyone can pick a new FORM type ID but should reserve it with Electronic
Arts at their earliest convenience. [Issue: EA contact person? Hand this
off to another organization?] While decentralized format definitions and
extensions  are  possible  in  IFF,  our  preference  is  to  get design
consensus  by  committee,  implement  a program  to  read  and write it,
perhaps  tune the format, and then publish the format with example code.
Some  organization  should remain in  charge  of answering questions and
coordinating extensions to the format.

If  it becomes necessary to revise the  design of some data section, its
FORM  type  ID  will serve as a  version  number  (Cf. Type IDs). E.g. a
revised  "VDEO"  data section could be called  "VDE1". But try to get by
with compatible revisions within the existing FORM type.

In   a   new  FORM  type,  the   rules  for  primitive  data  types  and
word-alignment  (Cf.  Primitive  Data Types)  may  be  overriden for the
contents  of its local chunks but not  for the chunk structure itself if
your  documentation spells out the  deviations. If machine-specific type
variants  are needed, e.g. to store  vast numbers of integers in reverse
bit  order,  then  outline  the  conversion  algorithm  and indicate the
variant  inside each file, perhaps via different FORM types. Needless to
say, variations should be minimized.

In  designing a FORM type, encapsulate  all the data that other programs
will  need to interpret your files.  E.g. a raster graphics image should
specify the image size even if your program always uses 320 x 200 pixels
x  3 bitplanes. Receiving programs are  then empowered to append or clip
the  image rectangle, to add or drop  bitplanes, etc. This enables a lot
more compatibility.

Separate  the  central data (like  musical  notes) from more specialized
information  (like  note  beams)  so  simpler  programs  can extract the
central parts during read-in. Leave room for expansion so other programs
can  squeeze in new kinds of  information (like lyrics). And remember to
keep the property chunks manageably short let's say 2 256 bytes.

When  designing  a data object, try to  strike a good tradeoff between a
super-general format and a highly-specialized one. Fit the details to at
least  one  particular  need, for example  a  raster image might as well
store  pixels  in the current machine's scan  order. But add the kind of
generality  that makes it usable with foreseeable hardware and software.
E.g.  use a whole byte for each red, green, and blue color value even if
this  year's  computer has only 4-bit  video  DACs. Think ahead and help
other  programs so long as the overhead is acceptable. E.g. run compress
a  raster by scan line rather than as a unit so future programs can swap
images by scan line to and from secondary storage.

Try  to  design  a general purpose  "least  common multiple" format that
encompasses  the needs of many programs without getting too complicated.
Let's  coalesce  our uses around a  few such formats widely separated in
the  vast design space. Two factors make this flexibility and simplicity
practical.  First,  file  storage space  is  getting  very plentiful, so
compaction  is not a priority. Second, nearly any locally-performed data
conversion  work during file reading and  writing will be cheap compared
to the I/O time.

It  must be ok to copy a LIST or FORM or CAT intact, e.g. to incorporate
it  into  a composite FORM. So any  kind of internal references within a
FORM must be relative references. They could be relative to the start of
the  containing FORM, relative from the referencing chunk, or a sequence
number into a collection.

With  composite FORMs, you leverage on existing programs that create and
edit  the  components.  If you write  a  program  that creates composite
objects,  please provide a facility for  your users to import and export
the  nested FORMs. The import and export functions may move data through
a separate file or a clipboard.

Finally, don't forget to specify all implied rules in detail.


5. LISTs, CATs, and Shared Properties

Data  often needs to be grouped together like a list of icons. Sometimes
a  trick  like  arranging  little images  into  a  big raster works, but
generally  they'll  need  to be structured  as  a first class group. The
objects "LIST" and "CAT" are IFF-universal mechanisms for this purpose.

Property  settings  sometimes need to be  shared  over a list of similar
objects.  E.g. a list of icons may  share one color map. LIST provides a
means  called "PROP" to do this. One purpose  of a LIST is to define the
scope  of a PROP. A "CAT", on  the other hand, is simply a concatenation
of objects.

Simpler  programs  may skip LISTs and  PROPs  altogether and just handle
FORMs and CATs. All "fully-conforming" IFF programs also know about "CAT
",  "LIST", and "PROP". Any program that reads a FORM inside a LIST must
process shared PROPs to correctly interpret that FORM.

Group CAT

A CAT is just an untyped group of data objects.

Structurally,  a  CAT  is  a chunk with  chunk  ID  "CAT  " containing a
"contents  type"  ID followed by the  nested objects. The ckSize of each
contained chunk is essentially a relative pointer to the next one.

CAT     ::= "CAT " #{ ContentsType (FORM | LIST | CAT)* }
ContentsType    ::= ID  -- a hint or an "abstract data type" ID

In  reading  a  CAT, like any  other  chunk,  programs must respect it's
ckSize  as a virtual end-of-file for  reading the nested objects even if
they're malformed or truncated.

The  "contents  type" following the CAT's  ckSize indicates what kind of
FORMs  are inside. So a CAT of ILBMs would store "ILBM" there. It's just
a  hint.  It may be used to store  an  "abstract data type". A CAT could
just  have blank contents ID ("JJJJ") if  it contains more than one kind
of FORM.

CAT defines only the format of the group. The group's meaning is open to
interpretation.  This is like a list in  LISP: the structure of cells is
predefined  but the meaning of the contents as, say, an association list
depends  on  use.  If  you need a  group  with  an  enforced meaning (an
"abstract   data  type"  or   Smalltalk  "subclass"),  some  consistency
constraints,  or  additional data chunks,  use  a composite FORM instead
(Cf. Composite FORMs).

Since  a  CAT  just means a  concatenation  of  objects, CATs are rarely
nested. Programs should really merge CATs rather than nest them.

Group LIST

A  LIST defines a group very much like CAT but it also gives a scope for
PROPs  (see below). And unlike CATs,  LISTs should not be merged without
understanding their contents.

Structurally,  a LIST is a chunk with ckID "LIST" containing a "contents
type"  ID,  optional shared properties,  and the nested contents (FORMs,
LISTs, and CATs), in that order. The ckSize of each contained chunk is a
relative pointer to the next one. A LIST is not an arbitrary linked list
the cells are simply concatenated.

LIST ::= "LIST" #{ ContentsType PROP* (FORM | LIST | CAT)* }
ContentsType    ::= ID

Group PROP

PROP  chunks  may  appear in LISTs (not  in  FORMs or CATs). They supply
shared  properties  for the FORMs in  that LIST. This ability to elevate
some  property  settings to shared status for  a list of forms is useful
for both indirection and compaction. E.g. a list of images with the same
size  and  colors  can  share one  "size"  property  and one "color map"
property. Individual FORMs can override the shared settings.

The contents of a PROP is like a FORM with no data chunks:

PROP ::= "PROP" #{ FormType Property* }

It means, "Here are the shared properties for FORM type <<FormType>."

A  LIST may have at most one PROP of a FORM type, and all the PROPs must
appear  before  any of the FORMs or  nested LISTs and CATs. You can have
subsequences  of  FORMs sharing properties  by making each subsequence a
LIST.

Scoping:  Think  of  property settings  as  variable  bindings in nested
blocks of a programming language. Where in C you could write:

TEXT_FONT text_font = Courier;  /* program's global default     */

File(); {
        TEXT_FONT text_font = TimesRoman;       /* shared setting       */

                {
                TEXT_FONT text_font = Helvetica;  /* local setting      */
                Print("Hello ");/* uses font Helvetica  */
                }

                {
                Print("there.");/* uses font TimesRoman */
                }
        }

An IFF file could contain:

LIST {
        PROP TEXT {
                FONT {TimesRoman}       /* shared setting       */
                }

        FORM TEXT {
                FONT {Helvetica}/* local setting*/
                CHRS {Hello }           /* uses font Helvetica  */
                }

        FORM TEXT {
                CHRS {there.}   /* uses font TimesRoman */
                }
        }

The shared property assignments selectively override the reader's global
defaults,  but  only for FORMs within  the  group. A FORM's own property
assignments  selectively override the  global and group-supplied values.
So  when reading an IFF file, keep property settings on a stack. They're
designed to be small enough to hold in main memory.

Shared   properties   are  semantically   equivalent  to  copying  those
properties  into  each of the nested  FORMs  right after their FORM type
IDs.

Properties for LIST

Optional  "properties for LIST" store the  origin of the list's contents
in  a PROP chunk for the fake  FORM type "LIST". They are the properties
originating  program  "OPGM",  processor  family  "OCPU",  computer type
"OCMP",  computer serial number or network address "OSN ", and user name
"UNAM".   In  our  imperfect  world,  these  could  be  called  upon  to
distinguish  between  unintended variations of a  data format or to work
around  bugs  in particular  originating/receiving program pairs. Issue:
Specify the format of these properties.

A  creation  date could also be stored  in a property but let's ask that
file  creating, editing, and transporting  programs maintain the correct
date  in the local file system. Programs that move files between machine
types are expected to copy across the creation dates.


6. Standard File Structure

File Structure Overview

An IFF file is just a single chunk of type FORM, LIST, or CAT. Therefore
an  IFF file can be recognized by  its first 4 bytes: "FORM", "LIST", or
"CAT ". Any file contents after the chunk's end are to be ignored.

Since  an  IFF file can be a  group of objects, programs that read/write
single   objects  can  communicate  to  an  extent  with  programs  that
read/write  groups. You're encouraged to  write programs that handle all
the  objects  in  a LIST or CAT.  A  graphics editor, for example, could
process  a  list of pictures as a  multiple page document, one page at a
time.

Programs  should enforce IFF's syntactic  rules when reading and writing
files.  This  ensures  robust  data  transfer.  The  public  domain  IFF
reader/writer  subroutine  package does this  for you. A utility program
"IFFCheck"  is  available  that  scans an  IFF  file  and  checks it for
conformance to IFF's syntactic rules. IFFCheck also prints an outline of
the  chunks  in the file, showing the  ckID  and ckSize of each. This is
quite  handy  when  building  IFF  programs.  Example  programs are also
available to show details of reading and writing IFF files.

A  merge program "IFFJoin" will be  available that logically appends IFF
files  into  a single CAT group. It  "unwraps" each input file that is a
CAT so that the combined file isn't nested CATs.

If  we need to revise the IFF  standard, the three anchoring IDs will be
used  as "version numbers". That's why IDs "FOR1" through "FOR9", "LIS1"
through "LIS9", and "CAT1" through "CAT9" are reserved.

IFF  formats are designed for  reasonable performance with floppy disks.
We  achieve  considerable  simplicity  in  the  formats  and programs by
relying  on the host file system rather than defining universal grouping
structures  like directories for LIST contents. On huge storage systems,
IFF  files could be leaf nodes in  a file structure like a B-tree. Let's
hope the host file system implements that for us!

Thre  are two kinds of IFF files:  single purpose files and scrap files.
They  differ  in the interpretation of  multiple data objects and in the
file's external type.

Single Purpose Files

A  single  purpose  IFF  file is  for  normal  "document"  and "archive"
storage.  This  is  in  contrast  with  "scrap  files"  (see  below) and
temporary backing storage (non-interchange files).

The  external  file type (or filename  extension,  depending on the host
file system) indicates the file's contents. It's generally the FORM type
of the data contained, hence the restrictions on FORM type IDs.

Programmers  and  users may pick an  "intended use" type as the filename
extension to make it easy to filter for the relevant files in a filename
requestor.  This is actually a "subclass" or "subtype" that conveniently
separates files of the same FORM type that have different uses. Programs
cannot  demand  conformity  to  its  expected  subtypes  without  overly
restricting  data interchange since they  cannot know about the subtypes
to  be  used  by future programs that  users  will want to exchange data
with.

Issue:  How  to generate 3-letter  MS-DOS  extensions from 4-letter FORM
type IDs?

Most  single  purpose files will be  a  single FORM (perhaps a composite
FORM   like  a  musical  score  containing  nested  FORMs  like  musical
instrument  descriptions). If it's a LIST or a CAT, programs should skip
over  unrecognized  objects  to read the  recognized  ones  or the first
recognized  one. Then a program that can  read a single purpose file can
read something out of a "scrap file", too.

Scrap Files

A  "scrap file" is for maximum interconnectivity in getting data between
programs;  the  core of a clipboard  function. Scrap files may have type
"IFF " or filename extension ".IFF".

A  scrap file is typically a CAT containing alternate representations of
the  same  basic  information. Include as  many  alternatives as you can
readily   generate.   This  redundancy   improves  interconnectivity  in
situations where we can't make all programs read and write super-general
formats. [Inside Macintosh chapter "Scrap Manager".] E.g. a graphically-
annotated musical score might be supplemented by a stripped down 4-voice
melody and by a text (the lyrics).

The  originating  program should write  the alternate representations in
order of "preference": most preferred (most comprehensive) type to least
preferred  (least comprehensive) type. A receiving program should either
use  the first appearing type that it  understands or search for its own
"preferred" type.

A scrap file should have at most one alternative of any type. (A LIST of
same  type objects is ok as one of the alternatives.) But don't count on
this  when reading; ignore extra sections of a type. Then a program that
reads scrap files can read something out of single purpose files.

Rules for Reader Programs

Here are some notes on building programs that read IFF files. If you use
the standard IFF reader module "IFFR.C", many of these rules and details
will  be automatically handled. (See  "Support Software" in Appendix A.)
We  recommend that you start from  the example program "ShowILBM.C". You
should  also  read up on recursive  descent  parsers. [See, for example,
Compiler Construction, An Advanced Course.]

%       The standard is very flexible so many programs can exchange
data. This implies a program has to scan the file and react to what's
actually there in whatever order it appears. An IFF reader program
is a parser.

%       For interchange to really work, programs must be willing to
do some conversion during read-in. If the data isn't exactly what
you expect, say, the raster is smaller than those created by your
program, then adjust it. Similarly, your program could crop a large
picture, add or drop bitplanes, and create/discard a mask plane. The
program should give up gracefully on data that it can't convert.

%       If it doesn't start with "FORM", "LIST", or "CAT ", it's not
an IFF-85 file.

%       For any chunk you encounter, you must recognize its type ID
to understand its contents.

%       For any FORM chunk you encounter, you must recognize its FORM
type ID to understand the contained "local chunks". Even if you don't
recognize the FORM type, you can still scan it for nested FORMs, LISTs,
and CATs of interest.

%       Don't forget to skip the pad byte after every odd-length chunk.

%       Chunk types LIST, FORM, PROP, and CAT are generic groups. They
always contain a subtype ID followed by chunks.

%       Readers ought to handle a CAT of FORMs in a file. You may treat
the FORMs like document pages to sequence through or just use the
first FORM.

%       Simpler IFF readers completely skip LISTs. "Fully IFF-conforming"
readers are those that handle LISTs, even if just to read the first
FORM from a file. If you do look into a LIST, you must process shared
properties (in PROP chunks) properly. The idea is to get the correct
data or none at all.

%       The nicest readers are willing to look into unrecognized FORMs
for nested FORM types that they do recognize. For example, a musical
score may contain nested instrument descriptions and an animation
file may contain still pictures.

Note to programmers: Processing PROP chunks is not simple! You'll
need some background in interpreters with stack frames. If this is
foreign to you, build programs that read/write only one FORM per file.
For the more intrepid programmers, the next paragraph summarizes how
to process LISTs and PROPs. See the general IFF reader module "IFFR.C"
and the example program "ShowILBM.C" for details.

Allocate  a  stack  frame  for every  LIST  and  FORM  you encounter and
initialize  it by copying the stack frame of the parent LIST or FORM. At
the  top level, you'll need a  stack frame initialized to your program's
global  defaults. While reading each LIST or FORM, store all encountered
properties  into the current stack frame.  In the example ShowILBM, each
stack  frame  has a place for a  bitmap  header property ILBM.BMHD and a
color  map  property ILBM.CMAP. When you  finally get to the ILBM's BODY
chunk, use the property settings accumulated in the current stack frame.

An  alternate  implementation  would  just  remember  PROPs encountered,
forgetting  each  on  reaching  the end of  its  scope  (the  end of the
containing  LIST).  When a FORM XXXX  is encountered, scan the chunks in
all  remembered  PROPs  XXXX, in order,  as  if they appeared before the
chunks  actually in the FORM XXXX. This  gets trickier if you read FORMs
inside of FORMs.

Rules for Writer Programs

Here  are some notes on building programs that write IFF files, which is
much easier than reading them. If you use the standard IFF writer module
"IFFW.C" (see "Support Software" in Appendix A), many of these rules and
details   will  automatically  be  enforced.  See  the  example  program
"Raw2ILBM.C".

%       An IFF file is a single FORM, LIST, or CAT chunk.

%       Any IFF-85 file must start with the 4 characters "FORM", "LIST",
or "CAT ", followed by a LONG ckSize. There should be no data after
the chunk end.

%       Chunk types LIST, FORM, PROP, and CAT are generic. They always
contain a subtype ID followed by chunks. These three IDs are universally
reserved, as are "LIS1" through "LIS9", "FOR1" through "FOR9", "CAT1"
through "CAT9", and "    ".

%       Don't forget to write a 0 pad byte after each odd-length chunk.

%       Four techniques for writing an IFF group: (1) build the data
in a file mapped into virtual memory, (2) build the data in memory
blocks and use block I/O, (3) stream write the data piecemeal and
(don't forget!) random access back to set the group length count,
and (4) make a preliminary pass to compute the length count then stream
write the data.

%       Do not try to edit a file that you don't know how to create.
Programs may look into a file and copy out nested FORMs of types that
they recognize, but don't edit and replace the nested FORMs and don't
add or remove them. That could make the containing structure inconsistent.
You may write a new file containing items you copied (or copied and
modified) from another IFF file, but don't copy structural parts you
don't understand.

%       You must adhere to the syntax descriptions in Appendex A. E.g.
PROPs may only appear inside LISTs.


Appendix A. Reference

Type Definitions

The  following C typedefs describe standard IFF structures. Declarations
to  use  in practice will vary with  the  CPU and compiler. For example,
68000  Lattice C produces efficient comparison code if we define ID as a
"LONG". A macro "MakeID" builds these IDs at compile time.

/* Standard IFF types, expressed in 68000 Lattice C.    */

typedef unsigned char UBYTE;    /*  8 bits unsigned     */
typedef short WORD;     /* 16 bits signed       */
typedef unsigned short UWORD;   /* 16 bits unsigned     */
typedef long LONG;      /* 32 bits signed       */

typedef char ID[4];     /* 4 chars in ' ' through '~'   */

typedef struct {
        ID      ckID;
        LONG    ckSize; /* sizeof(ckData)       */
        UBYTE   ckData[/* ckSize */];
        } Chunk;

/* ID typedef and builder for 68000 Lattice C. */
typedef LONG ID;        /* 4 chars in ' ' through '~'   */
#define MakeID(a,b,c,d) ( (a)<<<<24 | (b)<<<<16 | (c)<<<<8 | (d) )

/* Globally reserved IDs. */
#define ID_FORM   MakeID('F','O','R','M')
#define ID_LIST   MakeID('L','I','S','T')
#define ID_PROP   MakeID('P','R','O','P')
#define ID_CAT    MakeID('C','A','T',' ')
#define ID_FILLER MakeID(' ',' ',' ',' ')

Syntax Definitions

Here's a collection of the syntax definitions in this document.

Chunk   ::= ID #{ UBYTE* } [0]

Property::= Chunk

FORM    ::= "FORM" #{ FormType (LocalChunk | FORM | LIST | CAT)*
}
FormType::= ID
LocalChunk      ::= Property | Chunk

CAT     ::= "CAT " #{ ContentsType (FORM | LIST | CAT)* }
ContentsType    ::= ID  -- a hint or an "abstract data type" ID

LIST    ::= "LIST" #{ ContentsType PROP* (FORM | LIST | CAT)* }
PROP    ::= "PROP" #{ FormType Property* }

In this extended regular expression notation, the token "#" represents a
ckSize  LONG  count of the following  {braced} data bytes. Literal items
are  shown  in "quotes", [square bracketed  items] are optional, and "*"
means  0  or  more instances. A  sometimes-needed  pad  byte is shown as
"[0]".

Defined Chunk IDs

This  is a table of currently defined chunk IDs. We may also borrow some
Macintosh IDs and data formats.

Group chunk IDs
        FORM, LIST, PROP, CAT.
Future revision group chunk IDs
        FOR1 I FOR9, LIS1 I LIS9, CAT1 I CAT9.
FORM type IDs
        (The above group chunk IDs may not be used for FORM type IDs.)
        (Lower case letters and punctuation marks are forbidden in FORM
type IDs.)
        8SVX 8-bit sampled sound voice, ANBM animated bitmap, FNTR raster
font, FNTV vector font, FTXT formatted text, GSCR general-use musical
score, ILBM interleaved raster bitmap image, PDEF Deluxe Print page
definition, PICS Macintosh picture, PLBM (obsolete), USCR Uhuru Sound
Software musical score, UVOX Uhuru Sound Software Macintosh voice,
SMUS simple musical score, VDEO Deluxe Video Construction Set video.
Data chunk IDs
        "JJJJ", TEXT, PICT.
PROP LIST property IDs
        OPGM, OCPU, OCMP, OSN, UNAM.



Support Software

These  public domain C source programs are available for use in building
IFF-compatible programs:

IFF.H, IFFR.C, IFFW.C

                IFF reader and writer package.
                These modules handle many of the details of reliably
                reading and writing IFF files.

IFFCheck.C      This handy utility program scans an IFF file, checks
                that the contents are well formed, and prints an outline
                of the chunks.

PACKER.H, Packer.C, UnPacker.C

                Run encoder and decoder used for ILBM files.

ILBM.H, ILBMR.C, ILBMW.C

                Reader and writer support routines for raster image
                FORM ILBM. ILBMR calls IFFR and UnPacker. ILBMW calls
                IFFW and Packer.

ShowILBM.C
                Example caller of IFFR and ILBMR modules. This
                Commodore-Amiga program reads and displays a FORM ILBM.
Raw2ILBM.C
                Example ILBM writer program. As a demonstration, it
                reads a raw raster image file and writes the image
                as a FORM ILBM file.
ILBM2Raw.C
                Example ILBM reader program.  Reads a FORM ILBM file
                and writes it into a raw raster image.

REMALLOC.H, Remalloc.c

                Memory allocation routines used in these examples.

INTUALL.H       generic "include almost everything" include-file
                with the sequence of includes correctly specified.

READPICT.H, ReadPict.c

                given an ILBM file, read it into a bitmap and
                a color map

PUTPICT.H, PutPict.c

                given a bitmap and a color map, save it as
                an ILBM file.

GIO.H, Gio.c    generic I/O speedup package.  Attempts to speed
                disk I/O by buffering writes and reads.

giocall.c       sample call to gio.

ilbmdump.c      reads in ILBM file, prints out ascii representation
                for including in C files.

bmprintc.c      prints out a C-language representation of data for
                a bitmap.



Example Diagrams

Here's  a box diagram for an example IFF file, a raster image FORM ILBM.
This  FORM  contains  a bitmap header  property  chunk BMHD, a color map
property  chunk  CMAP,  and a raster  data  chunk  BODY. This particular
raster  is  320 x 200 pixels x  3 bit planes uncompressed. The "0" after
the CMAP chunk represents a zero pad byte; included since the CMAP ch