Liquid Tracker notes
Claudio Matsuoka <cmatsuoka@gmail.com>

A few notes regarding the Liquid Tracker module format details that
are not described in the official spec written by the author (Nir Oren).

1, Liquid Tracker versions

Here is a summary of the relevant module format changes in each release
from the changelog and some inference.

* 0.14b (30 09 1993)
  - Up to 64 channels

* 0.20b (12 10 1993)

* 0.21b (15 10 1993)

* 0.50b (27 11 1993)
  - Module format 0.00?
  - Global volume
  - No 16 bit samples
  - No finetunes
  - Samples up to 64 Kb
  - Sample name sizes increased to 22 bytes
  - Effects A-O, M0-MC, I0-I5. Reserved effects: F, H, M9, MA

  List of supported effects:
      - BPM tempos (Axx with value >$30  [not $1C] )
      - Portamento down (Dxx)
      - Portamento up (Exx)    | These are the effects from previous
      - Volume Slide (Lxx)     | versions of Liquid:
      - Finevolume up (M2x)    |
      - Finevolume up (M3x)    | - Cut pattern (Cxx)
      - Retrig note (M6x)      | - Position jump (Jxx)
      - Cut note (M7x)         | - Sample offset (Oxx)
      - Delay note (M8x)       |

  The effects that are currently implemented marked with '*':
 
        *  A = Adjust Tempo or BPM       M0 - Fineportamento up
           B = Vibrato                   M1 - Fineportamento down
        *  C = Cut pattern             * M2 - Fine volume up
        *  D = Portamento Down         * M3 - Fine volume down
        *  E = Portamento up             M4 - Vibrato waveform
           F = reserved                  M5 - Tremolo waveform
           G = Arpeggio                * M6 - Retrig note
           H = reserved                * M7 - Cut note
           I = Misc 1 (see list)       * M8 - Delay note
        *  J = Jump to position          M9 - reserved
           K = Tremolo                   MA - reserved
        *  L = Volume slide              MB - pattern loop (0=Mark)
           M = Misc 2 (see list)         MC - pattern delay
           N = Note portamento
        *  O = Sample offset             I0 - Vibrato + Volumeslide up
                                         I1 - Vibrato + Volumeslide down
           Waveforms:                    I2 - NotePort + Volumeslide up
                                         I3 - NotePort + Volumeslide down
           0) Sine Wave  2) Square       I4 - Tremolo + Volumeslide up
           1) Ramp Down  3) Ramp Up      I5 - Tremolo + Volumeslide down

* 0.60b (23 12 1993)
  - Most of ProTracker's effects are now implemented (and correctly,
    unlike some other trackers around)

* 0.63b (26 01 1994)

* 0.64b (03 02 1994)
  - Enhanced Break Pattern effect, now supports where-to-start value
  - Liquid is getting closer to be full ProTracker compatible:
    only left: Arpeggio, Waveforms, FineTunes, Gliss and Tremolo

* 0.65b (15 03 1994) Unreleased

* 0.67b (09 04 1994) Unreleased
  - Global volume (command Fxx)
  - Channel Panning (Command Hxx, 0 = Left, 32 = Middle, 64 = Right)
  - Arpeggio effect (Gxx) now supported
  - MODs now playing at correct panning

* 0.68b (25 04 1994)
  - "Reset panning" command (resets pan positions to default) - H70

* 0.69b (26 04 1994)

* 0.80b (03 12 1994)
  - 16bit and Stereo samples implemented
  - Added Full panning & surround
  
* 0.81b (15 12 1994)
  - Now volumes are rounded up. That means that if the master volume
    value is very low, you will still be able to hear the voices

* 0.82b (16 12 1994)

* 0.83b (22 12 1994)

* 0.83c (23 12 1994)

* 0.84b (06 01 1995)

* 0.85b (15 04 1995)

* 0.86b (22 06 1995)

* 0.90d (>= 1993) [Not in changelog!]
  - Module format 0.00
  - Known modules: 1 (WasteOfTime.liq)
  - max. 63 instruments? (``Another "YO" goes out to all of u out there
    I should have greeted but did not have the space to.. -Bye!-'')

* 1.00 (15 01 1996)
  - Max 100 instruments?
  - Added Fine Vibrato effect (ST 3.2 compatibility) - command 'F'

* 1.03 (11 03 1996)
  - There was "out of tune" problem when played portamento effects
    with S3M modules that contained high pitch samples (such as
    TALES01.S3M), now it's fixed.
  - Supports more than 16 channels in S3M loader (not supported by ST3 though)     
* 1.04 (23 03 1996)
  - speeds above 80 are supported
  
* 1.05 (18 05 1995)

* 1.06 (27 05 1996)
  - 16 bit volume precision for 16 bit samples
  
* 1.07 (29 06 1996)
  - Added module effect "P77 - Reset single channel PAN"

* 1.08 (09 08 1996)
  - Support for header's panning in new S3Ms (not widely used)

* 1.09 (<= Oct 1996) [Not in changelog!] [Not in changelog!] [Not in changelog!] [Not in changelog!]
  - Module format: 1.00
  - Known modules: 1 (BreakingTheShell.liq) - tracker version stated in
    the module

* 1.20 (12 10 1996)
  - LIQ module format and LDSS sample now documented 
  - Master volume for sample
  - Default pan for sample
  - Filename field
  - Global Volume effect. Use Gxx to set Global Volume (a decimal number
    ranging from 0 to 64, with initial value of 64). Note that it plays
    a bit different from the original ST3 (ST3 has bug which implements the
    effect only one row later)

* 1.25 (07 12 1996)

* 1.26 (10 01 1997)

* 1.27 (11 01 1997)

* 1.30 (09 03 1997)

* 1.31 (19 04 1997)
  - Bidirectional loops

* 1.32 (19 04 1997)

* 1.33 (03 05 1997)

* 1.50 (21 10 1997)
  - Echo pools

  

2. Known modules

I only have two LIQ modules, 'Waste of Time' (a Kenny Chou style melodic
synth-techno tune, sent by Miod Vallat) and 'Breaking the Shell' (a piano
tune). xmp currently plays both :)

   Title			Author		Version	Tracker
   ----------------------------	---------------	-------	------------------
   Waste of Time  [The Chomp] 	Moti Radomski	0.00	LiquidTrackr0.90d
   <Breaking the Shell> / DOC	Adi Sapir	1.00	LiquidTrackr1.25ÿ


3. Header loading


4. Pattern loading

The description on the official spec isn't clear on many aspects of
pattern decoding and loading. Here's what I implemented in xmp:

- In each pattern, tracks are stored sequentially. End of pattern is
  marked by 0xc0, end of tracks are not marked.
- Event repeats should not cross track boundaries.
- If (0xa0 < NOTE < 0xc0), the event bitmask (NOTE) is not read again
  for the next events.
- If (0x80 < NOTE < 0xa0), the event bitmask (NOTE) is read again for
  each event.
- Unpacked events may contain only note if instrument > 100. In this
  case the instrument value is a new event bitmask.


