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# gslaplay
Apple IIgs GSLA Player
# gslaplay - Apple IIgs GSLA Player
Example of a GS LZB Animation Player
Program that plays GS LZB Animation files.
Inspired by Deluxe Animation Run/Skip/Dump, and FLI/FLC with similar properties
-----
New Apple IIgs Animation file format ... GS LZ Byte Compressed Animation
> Why? When there are so many image formats would we need another one?
> It's because $C2/Paintworks animation format is just terribly inefficient.
I replace the "Run" with a dictionary/frame buffer copy from the existing
buffer to the existing buffer. This is able to runlength not just a single
byte, but a repeating pattern of arbitrary length.
- Inspired by Deluxe Animation Run/Skip/Dump, and FLI/FLC with similar properties.
- I replace the "Run" with a dictionary/frame buffer copy from the existing buffer to the existing buffer. This is able to runlength not just a single byte, but a repeating pattern of arbitrary length.
- Care is taken in the encoder to make sure the 65816 does not have to cross bank boundaries during any copy. This is so we can use the MVN instruction and also reduce the number of bank checks in the code.
-- (We have an opcode to indicate "source data bank has changed".)
- Goals include a good balance between file size, and playback performance (since one often makes a trade off with the other).
--------------------------------------------------------------------------------
New Apple IIgs Animation file format
GS LZ Byte Compressed Animation
Why? When there are so many image formats would we need another one? It’s
because $C2/Paintworks animation format is just terribly inefficient.
Care is taken in the encoder, to make sure the 65816 does not have to cross bank
boundaries during any copy. This is so we can use the MVN instruction, and so
we can reduce the number of bank checks in the code.
We have an opcode, that says “source data bank has changed”
Goals include a good balance between file size, and playback performance
(since one often makes a trade off with the other).
The file is defined as a byte stream.
I will attempt to define the format as
file-offset: the thing that is at the offset
Header of the File is 20 bytes as follows
File Offset Data Commentary
------------------------------------------------------------------
0 0x47 ; ‘G’ Graphics
1 0x53 ; ‘S’
2 0x4C ; ‘L’ LZB
3 0x41 ; ‘A’ Animation
; File Length, is the total length of the file
4 FileLengthLow ; Low byte, 32-bit file length
5 LengthLowHigh ; High byte of low word
6 LengthHighLow ; Low byte, of high word
7 LengthHighHigh ; High Byte, of high word
; 16 bit word with version #
8 VL ; Version # of the file format, currently only version 0
9 VH ; Version High Byte
; %RVVV_VVVV_VVVV_VVVV
; V is a version #, 0 for now
; R is the MSB, R = 0 no ring frame
; R = 1, there is a ring frame
; A Ring Frame is a frame that will delta from the last
; frame of the animation, back to the first, for smoother
; looping , If a ring frame exists, it’s also in the
; frame count
// next is a word, width in bytes (only 160 for now)
0xA WL ; Display Width in bytes low byte
0xB WH ; Display Width in bytes high byte
// next is a word, height (likely 200 for now, in tiled mode a multiple of 16)
0xC HL ; Display Height in bytes, low byte
0xD HH ; Display Height in bytes, high byte
// 2 bytes, Frame Size in Bytes, since a “Frame” may contain more than just the
// width * height, worth of pixels, for now this is $8000, or 32768
0xE FBL ; Frame Buffer Length Low
0xF FBH ; Frame Buffer Length High
// 4 byte, 32-bit, Frame Count (includes total frame count, so if there is a
// ring frame, this is included in the total)
0x10 FrameCountLow
0x11 FrameCountLowHigh
0x12 FrameCountHighLow
0x13 FrameCountHigh
-----
After this comes AIFF style chunks of data, basically a 4 byte chunk name,
followed by a 4 byte length (inclusive of the chunk size). The idea is that
you can skip chunks you don’t understand.
## Format
The file has an initial header followed by multiple data chunks.
### Header
Header of the File is 20 bytes as follows:
File Offset | Data | Comment
------------|:----------------------:|------------------------------------
| | _File ID_ |
0 | `0x47` | 'G' Graphics
1 | `0x53` | 'S'
2 | `0x4C` | 'L' LZB
3 | `0x41` | 'A' Animation
4 | {FileLength} | (32-bit long) File length in bytes
8 | {VL} | Version Low - File format Minor version, `0` for now
9 | {VH} | Version High - Bits: ```%RVVV_VVVV_VVVV_VVVV```
| | | `V` is Major version #, `0` for now
| | | `R` is the MSB, `R = 0` no ring frame
| | | `R = 1`, there is a ring frame
| | | _Ring Frame_ is a frame that will delta from the last frame of the animation back to the first for smoother looping. If a ring frame exists, it's also in the frame count.
0xA | {Width} `0x00A0` | (16-bit word) Width in bytes, typically 320/2 == 160 == 0x00A0
0xC | {Height} `0x00C8` | (16-bit word) Height in bytes, typically 200 == 0x00C8
0xE | {FrameLength} `0x8000` | (16-bit word) Frame size in bytes, since a "Frame" may contain more than just the width * height, worth of pixels. For now this is `$8000`, or 32768
0x10 | {FrameCount} | (32-bit long) Frame Count (total, including ring frame)
0x14 | _First data chunk...._ | ....
... | _Next data chunk...._ | .... until end of file
After the header comes AIFF style chunks of data starting at file offset `0x14`, basically a 4-byte chunk name, followed by a 4-byte length (inclusive of the chunk header). The idea is that you can skip chunks you don't understand.
File Offset:
0x14 First Chunk (followed by more Chunks, until end of file)
Chunk Definitions
Name: ‘INIT’ - Initial Frame Chunk, this is the data used to first
initialize the playback buffer
0: 0x49 ; ‘I’
1: 0x4E ; ‘N’
2: 0x49 ; ‘I’
3: 0x54 ; ‘T’
// 32 bit long, length, little endian, including the 8 byte header
4: length low low
5: length low high
6: length high low
7: length high high
### Data Chunk Definitions
##### INIT
Initial Frame Chunk, this is the data used to first initialize the playback buffer
8: This is a single frame of data, that decodes/decompresses into frame sized
bytes (right now 0x8000)
This data stream includes, an end of animation opcode, so that the normal
animation decompressor, can be called on this data, and it will emit the initial
frame onto the screen
File Offset | Data | Comment
------------|:----------------------:|------------------------------------
0 | `0x49` | 'I'
1 | `0x4E` | 'N'
2 | `0x49` | 'I'
3 | `0x54` | 'T'
4 | {ChunkLength} | (32-bit long) Chunk length in bytes, including this 8-byte header
8 | {FrameData} | A single frame of data which will be decoded/decompressed into a frame-sized buffer (right now `0x8000`). This data stream includes, an end of animation opcode, so that the normal animation decompressor can be called on this data and it will emit the initial frame onto the screen.
Name: ‘ANIM’ - Frames
0: 0x41 ‘A’
1: 0x4E ‘N’
2: 0x49 ‘I’
3: 0x4D ‘M’
// 32 bit long, length, little endian, including chunk header
4: length low low
5: length low high
6: length high low
7: length high high
##### ANIM
Animation Frame Chunk, contains the encoded delta frame data for all of the frames
// This is followed by the frames, with the intention of decompressing them at
// 60FPS, which is why no play speed is included, if you need a play-rate slower
// than this, blank frame’s should be inserted into the animation data
Chunk Offset| Data | Comment
------------|:----------------------:|------------------------------------
0 | `0x41` | 'A'
1 | `0x4E` | 'N'
2 | `0x49` | 'I'
3 | `0x4D` | 'M'
4 | {ChunkLength} | (32-bit long) Chunk length in bytes, including this 8-byte header
8 | {FrameData} | Frames data stream, intended to be decompressed at 60FPS, which is why no play speed is included. If you need a play-rate slower than this, blank frames should be inserted into the animation data
// Every attempt is made to delta encode the image, meaning we just encode
// information about what changed each frame. We attempt to make the size
// efficient by supporting dictionary copies (where the dictionary is made up of
// existing pixels in the frame buffer).
> Every attempt is made to delta encode the image, meaning we just encode information about what changed each frame. We attempt to make the size efficient by supporting dictionary copies (where the dictionary is made up of existing pixels in the frame buffer).
### Decoding Chunk Data
Command Word, encoded low-high, what the bits mean:
// xxx_xxxx_xxxx_xxx is the number of bytes 1-16384 to follow (0 == 1 byte)
`xxx_xxxx_xxxx_xxx` is the number of bytes 1-16384 to follow (0 == 1 byte)
* %0xxx_xxxx_xxxx_xxx1 - Copy Bytes - straight copy bytes
* %1xxx_xxxx_xxxx_xxx1 - Skip Bytes - skip bytes / move the cursor
* %1xxx_xxxx_xxxx_xxx0 - Dictionary Copy Bytes from frame buffer to frame buffer
*
* %0000_0000_0000_0000- Source Skip -> Source pointer skips to next bank of data
* %0000_0000_0000_0010- End of Frame - end of frame
* %0000_0000_0000_0110- End of Animation / End of File / no more frames
`%0xxx_xxxx_xxxx_xxx1` - Copy Bytes - straight copy bytes
`%1xxx_xxxx_xxxx_xxx1` - Skip Bytes - skip bytes / move the cursor
`%1xxx_xxxx_xxxx_xxx0` - Dictionary Copy bytes from frame buffer to frame buffer
// other remaining codes, are reserved for future expansion
`%0000_0000_0000_0000` - Source Skip -> Source pointer skips to next bank of data
`%0000_0000_0000_0010` - End of Frame - end of frame
`%0000_0000_0000_0110` - End of Animation / End of File / No more frames
- other remaining codes, are reserved for future expansion