[New feature] LFO shaping

[sylvia-leaf]

Is your feature request related to a problem? Please describe.
Many synthesisers allow the use of different LFOs beyond sine LFO.

Describe the solution you'd like
Add LFO shapes such as triangle, saw, square, sample and hold, etc.

Describe alternatives you've considered
Baking LFO into samples, but this limits flexibility (some effects are not achievable), and increases file size.

Additional context
Thanks to @nehochupechatat for suggesting this!

[nehochupechatat]

I have studied the SF2 format in advance and a practical way to implement this for SFe 4 would likely be to reserve a generator enumeration number.

[enum number] = VibLFOShape with 1 argument.
[enum number] = ModLFOShape with the same kind of argument.

The argument is an enum:
0 = sine
1 = saw
2 = reverse saw
3 = square
4 = reverse square
5 = triangle

This is for full parity with the Beatnik HSB format

[nehochupechatat]

For a more radical change for parity with my advanced envelope format, I suggest a new riff chunk

Name: modu

uint8 type_1, enum:
0 = pitch
1 = volume
2 = frequency (low pass)
3 = frequency (high pass)
4 = frequency (band pass)
5 = resonance

uint8 type_2, enum:
0 = regular envelope (envl chunk)
1 = LFO
2 = LFO w/envelope

uint8 lfoShape, enum:
0 = sine
1 = saw
2 = reverse saw
3 = square
4 = reverse square
5 = triangle

Then, an envl sub-chunk

Then it kind of loops until no modulators are left, variable length.

envl chunk proposal:
#137

[nehochupechatat]

struct imod/pmod
[
SFGenerator GeneratorEnums (key range, lowpass, high pass, resonance, tuning scale)
SFGenerator GeneratorValues (for the above)
envl sub-chunk
modu sub-chunk
]

Basically like that for every instrument/preset zone.

While I understand that this breaks SF2 compatibility, SFe is a new format, so... And this isn't as radical as SFe 5 which would feature procedurally generated waves and FM synthesis

[stgiga]

None of this angers me.

[nehochupechatat]

Yeah, but we still need Sylvia and Stanley's input..