Turn Qxy and Rxy into portamento

FamiTracker measures pitch slides in "units". In FamiTracker 0.4.6 and 0CC-FamiTracker by default, units are raw period register units: smaller at low pitches and larger at high pitches. But the 0CC-FamiTracker fork has an option to instead use "linear pitch", which redefines a "unit" as 1/32 semitone (about 3 cents) no matter whether the pitch is high or low. (See 0CC-readme section "Linear Pitch Mode".)

Vibrato and portamento in Pently also use linear pitch, with 256 internal units per semitone. But for the purpose of this feature request, I will convert everything to 0CC-FT linear pitch units (1/32 semitone).

Pently supports an effect EPxx, which behaves much like FT's 3xx, but the rate ranges are different, with EP0x going at x semitones per frame and EP1x using an exponential scale.

EP code	Units/frame	0CC-FT effects
`EP10`	0.5
`EP11`	1	`Q0x`, `R0x`
`EP12`	1.5
`EP13`	2
`EP14`	3	`Q1y`, `R1y`
`EP15`	4	`Q2y`, `R2y`
`EP16`	6	`Q3y`, `R3y`
`EP17`	8	`Q4y` ,`R4y`
`EP18`	12	`Q5y`, `Q6y`, `R5y`, `R6y`
`EP19`	16	`Q7y`-`Q9y`, `R7y`-`R9y`
`EP1A`	24	`QAy`-`QDy`, `RAy`-`RDy`
`EP01`	32	`QEy`, `REy`
`EP1B`	48
`EP02`	64
`EP03`	96
`EP04`	128
`EP05`	160
`EP06`	192
`EP07`	224
`EP08`	256
`EP00`	Instant	`QFy`, `RFy`

I will limit this particular feature request to the Qxy and Rxy effects, as they are probably the most musically useful when not simulating percussion.

Qxy: Pitch slide up y semitones at 2*x+1 units per frame, then 300 before next note
Rxy: Pitch slide down y semitones at 2*x+1 units per frame, then 300 before next note

It's easiest to explain if the Qxy or Rxy is not on the same row:

F-3 .. . ...
... .. . R45
... .. . ...
... .. . ...

This means "Play a C-3 for one row, then on the next row, slide up to F-3 (which is 5 notes up) at 9 units per frame (which is 4 * 2 + 1)." It might become this:

f'16( EP17 c'8.) EP00

This means "Play an f' sixteenth note, turn on legato, set pitch slide to 8 units per frame, play a c' dotted eighth note, turn off legato, and disable pitch slide." Because 9 units per frame does not exist in Pently, the converter would round it to 8, whose code is EP17.

Qxy and Rxy on the same row as a note are slightly tricker. There appears to be currently a quirk in Pently that causes portamento to miss a new note pitch unless a note has been active for at least 2 frames. So this pattern fragment:

C-3 .. . Q45
... .. . ...
... .. . ...
... .. . ...

It means "Play a C-3, and on the same row, slide up to F-3 at 9 units per frame that continues until the start of the following note." A plausible translation:

c'2g( EP17 f'4) EP00

This means "Play a c' that lasts 2 frames, turn on legato, set pitch slide to 8 units per frame, play an f' quarter note, turn off legato, and disable pitch slide."

I choose to map QFy and RFy to instant pitch change (EP00) because a member of the FT users' Discord server recommended it as a replacement for the legato effect.

I have uploaded a 0CC-FamiTracker module and a plausible hand-translation into a Pently score.

Qxx_Rxx.0cc.zip Qxx_Rxx.pently.txt

NovaSquirrel / ft2pently

Turn Qxy and Rxy into portamento #24