doug@certes.UUCP (07/08/87)
[Dear LineEater: I live at ucbvax!unisoft!certes!doug; "reply" doesn't work!]
The new IFF ANIM form is out...Allen Hastings says that it has been recently
registered with Commodore, but possibly too recently for it to be part of
the IFF docs. For those of you who want to know *now*, here's a description
of it (I got this off FAUG disk #49, released tonight). I appended a line
marking the end of the document, so you'll know whether you got the whole
thing or not. Document follows signature below.
Some "BTW" comments: A demo made with Videoscape 3D is also now making the
rounds on BBS's and PD disks. And Leo showed his stereoscopic 3D hacks at the
meeting, using the StereoTek glasses interfaced to the Amiga. Fun! When I
first posted the news about these glasses (interfaced to the ST) months ago,
George Robbins was kind enough to offer some comments about how an Amiga
interface could work. Sure enough, that's exactly what Leo & Gary & Co. have
done...it plugs into mouse port two to sync with the frame rate. Leo also says
that his response to the BADGE Killer Demo Contest will *not* be stereoscopic
(awww!!) because they'd have to distribute the glasses with every PD disk
that carried the winners. Hmmm, now *there's* an idea!
Wendy ("my name is NOT A-Squared!" but could've fooled me) says that the
bottom line about why LIVE had so many problems is that: A-Squared designed
it, and sold the manufacturing rights to Commodore, who then sat on it and
apparently refused (?) to make and ship the d*mn things. A-Squared then
worked for lo, these many months, to get the rights back. Never mind recent
history; at least that partially explains ancient history. Perhaps everybody
already knew all this, but it was news to me. (I still don't know why it
was then transferred to GRAB after A-Squared was supposedly making it.)
Doug Merritt ucbvax!unisoft!certes!doug
/************************** CUT HERE *********************************/
>>> NEW IFF ANIMATION FORM: ANIM <<<
A N I M
An IFF Format For CEL Animations
June 18, 1987
prepared by:
Sparta Inc.
23041 de la Carlota
Laguna Hills, Calif 92653
714) 768-8161
contact: Gary Bonham
also by:
Aegis Development Co.
2115 Pico Blvd.
Santa Monica, Calif 90405
213) 392-9972
1.0 Introduction
The ANIM IFF format was developed at Sparta originally for the
production of animated video sequences on the Amiga computer. The
intent was to be able to store, and play back, sequences of frames and
to minimize both the storage space on disk (through compression) and
playback time (through efficient de-compression algorithms). It was
desired to maintain maximum compatibility with existing IFF formats and
to be able to display the initial frame as a normal still IFF picture.
The basic ANIM format described here has been in use for over a year
in-house at Sparta with the XOR mode. The delta mode is a recent, and
very effective, addition/improvement.
1.1 IFF File Format Overview
The general philosophy of ANIMs is to present the initial frame as a
normal, run-length-encoded, IFF picture. Subsequent frames are then
described by listing only their differences from a previous frame.
Normally, the "previous" frame is two frames back as that is the
frame remaining in the hidden screen buffer when double-buffering is
used. To better understand this, suppose one has two screens, called
A and B, and the ability to instantly switch the display from one to
the other. The normal playback mode is to load the initial frame
into A and duplicate it into B. Then frame A is displayed on the
screen. Then the differences for frame 2 are used to alter screen B
and it is displayed. Then the differences for frame 3 are used to
alter screen A and it is displayed, and so on. Note that frame 2 is
stored as differences from frame 1, but all other frames are stored
as differences from two frames back.
ANIM is an IFF FORM and its basic format is as follows (this assumes
the reader has a basic understanding of IFF format files):
FORM ANIM
. FORM ILBM first frame
. . BMHD normal type IFF data
. . CMAP
. . BODY
. FORM ILBM frame 2
. . ANHD animation header chunk
. . DLTA delta mode data
. FORM ILBM frame 3
. . ANHD
. . DLTA
...
The initial FORM ILBM can contain all the normal ILBM chunks, such as
CRNG, etc. The BODY will normally be a standard run-length-encoded
data chunk (but may be any other legal compression mode as indicated
by the BMHD).
The subsequent FORMs ILBM contain an ANHD, instead of a BMHD, which
duplicates some of BMHD and has additional parameters pertaining to
the animation frame. The DLTA chunk contains the data for the two
available delta compression modes. If the older XOR compression mode
is used, then a BODY chunk will be here. In addition, other chunks
may be placed in each of these as deemed necessary (and as code is
placed in player programs to utilize them). A good example would be
CMAP chunks to alter the color palette. A basic assumption in ANIMs
is that the size of the bitmap, and the display mode (e.g. HAM) will
not change through the animation.
1.2 Recording ANIMs
To record an ANIM will require three bitmaps - one for creation of
the next frame, and two more for a "history" of the previous two
frames for performing the compression calculations (e.g. the delta
mode calculations).
There are three frame-to-frame compression methods currently
defined:
1.2.1 XOR mode
This mode is the original and is included here for compatibility
with some programs which still can output this mode. In general,
the delta modes are far superior. The creation of XOR mode is
quite simple. One simply performs an exclusive-or (XOR) between
all corresponding bytes of the new frame and two frames back. This
results in a new bitmap with 0 bits wherever the two frames were
identical, and 1 bits where they are different. Then this new
bitmap is saved using run-length-encoding. A major obstacle of
this mode is in the time consumed in performing the XOR upon
reconstructing the image.
1.2.2 Long Delta mode
This mode stores the actual new frame long-words which are
different, along with the offset in the bitmap. The exact format
is shown and discussed in section 2 below. Each plane is handled
separately, with no data being saved if no changes take place in a
given plane. Strings of 2 or more long-words in a row which
change can be run together so offsets do not have to be saved for
each one.
Constructing this data chunk usually consists of having a buffer
to hold the data, and calculating the data as one compares the new
frame, long-word by long-word, with two frames back.
1.2.3 Short Delta mode
This mode is identical to the Long Delta mode except that
short-words are saved instead of long-words. In most instances,
this mode results in a smaller DLTA chunk. The Long Delta mode is
mainly of interest in improving the playback speed when used on a
32-bit 68020 Turbo Amiga.
1.3 Playing ANIMs
Playback of ANIMs will usually require two buffers, as mentioned
above, and double-buffering between them. The frame data from the
ANIM file is used to modify the hidden frame to the next frame to be
shown. When using the XOR mode, the usual run- length-decoding
routine can be easily modified to do the exclusive-or operation
required. Note that runs of zero bytes, which will be very common,
can be ignored, as an exclusive or of any byte value to a byte of
zero will not alter the original byte value.
2.0 Chunk Formats
2.1 ANHD Chunk
The ANHD chunk consists of the following data structure:
UBYTE operation (=0 set directly,
=1 XOR mode,
=2 Long Delta mode,
=3 Short Delta mode)
UBYTE mask (XOR mode only - plane mask where each bit is
set =1 if there is data and =0 if not.)
UWORD w,h (XOR mode only - width and height of the area
represented by the BODY to eliminate
unnecessary un-changed data)
WORD x,y (XOR mode only - position of rectangular area
representd by the BODY)
ULONG abstime (currently unused - timing for a frame relative
to the time the first frame was displayed - in
jiffies (1/60 sec))
ULONG reltime (timing for frame relative to time previous
frame was displayed - in jiffies (1/60 sec))
UBYTE interleave (unused so far - indicates how may frames back
this data is to modify. =0 defaults to
indicate two frames back (for double
buffering). =n indicates n frames back. The
main intent here is to allow values of =1 for
special applications where frame data would
modify the immediately previous frame)
UBYTE pad[21] (this is a pad for future use for future
compression modes. Some of these - maybe 16 -
are intentionally provided for use by Jim Kent
for operation codes for each plane and other
ancillary data he requested)
2.2 DLTA Chunk
This chunk is a basic data chunk used to hold the delta compression
data. The minimum size of this chunk is 32 bytes as the first 8
long-words are byte pointers into the chunk for the data for each of
up to 8 bitplanes. The pointer for the plane data starting
immediately following these 8 pointers will have a value of 32 as the
data starts in the 33-rd byte of the chunk (indes value of 32 due to
zero-base indexing).
The data for a given plane consists of groups of data words. In Long
Delta mode, these groups consist of both short and long words - short
words for offsets and numbers, and long words for the actual data. In
Short Delta mode, the groups are identical except data words are also
shorts so all data is short words. Each group consists of a starting
word which is an offset. If the offset is positive then it indicates
the increment in long or short words (whichever is appropriate)
through the bitplane. In other words, if you were reconstructing the
plane, you would start a pointer (to shorts or longs depending on the
mode) to point to the first word of the bitplane. Then the offset
would be added to it and the following data word would be placed at
that position. Then the next offset would be added to the pointer
and the following data word would be placed at that position. And so
on... The data terminates with an offset equal to 0xFFFF.
A second interpretation is given if the offset is negative. In that
case, the absolute value is the offset+2. Then the following
short-word indicates the number of data words that follow. Following
that is the indicated number of contiguous data words (longs or
shorts depending on mode) which are to be placed in contiguous
locations of the bitplane.
If there are no changed words in a given plane, then the pointer in
the first 32 bytes of the chunk is =0.
/**************************** END OF DOCUMENT ************************/