[New feature] Envelope shaping

[sylvia-leaf]

Is your feature request related to a problem? Please describe.
Beatnik includes pitch and volume envelope shaping functionality, which allows control of envelopes with "lines."

Describe the solution you'd like
Include such functionality to allow faithful recreation of envelope effects that are used in some mobile phones using the open-source miniBAE sound engine, or OpenMPT.

Describe alternatives you've considered
N/A

Additional context
Thanks to @nehochupechatat for suggesting this!

[nehochupechatat]

Those aren't just pitch envelopes but volume envelopes too.

MiniBAE was featured on pretty much every Nokia cellphone until 2005, and on low end devices until 2010, so millions know the sound of it

[nehochupechatat]

Proposal for this feature

RIFF chunk:

Name "envl", variable length depending on how many lines are there.
uint8 line_type, enum:
0 = regular Attack/Decay (non sustained) line
1 = sustain line (for decay to the sustained level)
2 = release lines (for release control)

float envelope_percentage;

float/double timecents (to get to envelope_percentage)

Then it just loops until the last listed envelope.

When not a sub-chunk of a "modu" chunk, it's a volume envelope

[stgiga]

Apparently the Moog Piano in JSBF V14 on Itch is broken in that the whole sample loops, and I don't know the best way of fixing it given that Polyphone auto loop alters the actual sample data.

[LoveBodhi]

Vaporizer2-style envelope system should be fine...