Animations

ANI/AFUL010..012.LIB are not animations. Each is 48 MiB of filler with no archive table.

BbhdHeader      70 bytes, at 0
BbfrRecord      frame record 0, at 0x46
BbfrRecord      frame record 1, at 0x46 + length of record 0
...
BbfrRecord      last frame record, at last_record_offset
BbftTrailer     12 bytes
0xff            one pad byte, only when the clip length is odd

The records form a chain in both directions. Each record stores its own length and the length of the record before it, and the header and trailer both point at the first and last record. A reader can therefore walk the clip forwards from the header or backwards from the trailer.

Every offset is relative to the start of the clip. The archive table does not record clip lengths; clip_length gives the length without the pad byte.

A clip always starts with a whole picture. In clips with flags 3, an anchor (a whole picture with bit 14 set in frame_number) usually follows every 11 records, the first one at record 11. A few clips place the first anchor at record 2 or 4, or space later anchors more closely.

In forward play the game passes over anchors. Its frame counter counts records, but it skips an anchor's number, so the step that would land on an anchor goes straight to the next record and takes no longer than any other step. A decoder should therefore show one picture per record that is not an anchor; showing the anchors too holds every eleventh picture for an extra step. In all 63 clips with flags 3, the anchors are exactly the records that repeat the previous picture without being repeat records.

Some whole pictures decompress to more than width * height bytes. The extra bytes (20, 100 or 18 of them) are left over from the tool that made the files: zeros, or fragments of its memory such as the text SWEN. Readers should use the first width * height bytes and ignore the rest.

Types 2 and 3 store the difference from the previous picture. The stream is ordered the way VGA "Mode X" memory is laid out: by plane, then by column, then top to bottom. Each changed value is combined with the old pixel by exclusive-or (XOR), so applying the same change twice restores the original.

for plane in 0..3:
  for x in plane, plane + 4, plane + 8, ... below width:
    loop:
      y_start = next byte            # 1-based row; 0 ends this column
      if y_start == 0: break
      count = next byte as signed
      y = y_start - 1
      if count > 0:                  # count different values
        repeat count times: pixel[x, y] ^= next byte; y += 1
      if count < 0:                  # one value, -count times
        value = next byte
        repeat -count times: pixel[x, y] ^= value; y += 1

Columns with no changes are a single 0 byte. After the last column, 2,575 of the 2,904 compressed change streams carry 20 more bytes, 00 01 02 ... 13. They are not part of the stream and are ignored.

The stream is a sequence of groups. Each group starts with a flag byte whose bits, highest first, describe the next eight items. A 0 bit is one literal byte, copied to the output. A 1 bit is a two-byte copy instruction a b:

count    = (a & 0x0f) + 3              # 3..18 bytes
distance = b + (a >> 4) * 256          # 1..4095 bytes back
copy count bytes, one at a time, from output[length - distance]

The copy may overlap the bytes it is producing, which repeats a short pattern. Decompression stops when unpacked_length bytes have been written.

ANI/ASCR000.LIB holds 256 scripts, ASCR000 to ASCR255. They are plain DOS text, one command per line; there is no compiled form on the disc. 125 of them contain no commands. A script runs on a clock of 25 ticks per second (40 ms per tick), counted from the start of the scene.

initpal (15,  0,  1)
rem  EFF,LNA,LNR,ENR,PMO,FRQ,BGN,DUR,END,PRI,STX,STY,DTX,DTY,WIL,WIT,WIW,WIH)
play ( 1, 32,  0, 43,  0,  8,  0, 10,  0,  0,  0,  0,  0,  0,  0,  0,120, 64)
play ( 3, 31,  0, 69,  0, 12, 10,290,  2,  0,  0,  0,  0,  0,  0,  0,120, 64)
End  ( 300 )

The rem lines are the authors' own comments; the argument names on this page come from them. Some lines carry stray text after the closing bracket, such as gto; it has no known effect.

The scripts mix upper and lower case (End, BLEND). The screen they draw on is 360x240 pixels.

play arguments

Other commands

write(TNA, TNR, TID, BGN, DUR, PRI, STY, SCO, PMA, PMB, PMC, ALG, BBH, WIL, WIT, WIW, WIH) shows text record TID of ENG/ATXT### (number TNR) in the window WIL..WIH from tick BGN for DUR ticks. STY=100 shows it at once and STY=101 types it out with a cursor. ALG sets the alignment: 0 left, 1 justified, 2 right, 3 centred. Fonts and colours are chosen by control codes inside the text record, not by write arguments.

fx(channel, bank, sound, BGN, volume, repeat) plays effect sound at tick BGN. A negative BGN ties the sound to the typed text instead of a tick; the scripts use -1 for the cursor sound and -2 for the line-return sound.

initpal(selector, archive, entry) and BLEND(selector, fromArchive, fromEntry, selector, toArchive, toEntry, low, high, begin, end) name palettes in ANI/APAL###. A fade changes only the colours low..high, starts from the palette it names (not from what is on screen) and lasts at most 127 ticks. A fade changes colours only; it never creates in-between pictures.

clear(begin, colour, left, top, width, height) clears a rectangle at tick begin. The second argument is 0 in every script and is probably the fill colour. End(ticks) ends the scene.