Blend mode: blend between snapshots

[sastraxi]

This PR introduces "blend mode", which allows a single analog input (e.g. the expression pedal) to interpolate parameter values between multiple snapshots. This is essentially a workaround for the fact that MOD pedalboard does not let you map multiple MIDI CCs to control the same parameter, and also that it does not seem to let you change the extents easily (at least in the UI).

The workflow is such: create your pedalboard, attach footswitches for MIDI controls as usual, etc. Then, create one or more snapshots that make the board sound to your liking. We can then create a new "Blend Mode" preset by configuring the pedalboard.

Configuration

In $HOME/.pedalboards/$PEDALBOARD/config.yml:

blend_snapshots:
  - name: "Clean to Fuzz"          # Required: descriptive name for this blend snapshot
    input_id: 0                    # Required: expression pedal (0) or encoder (1, 2)
    interpolation: linear          # Optional: interpolation function (default: linear)
                                   # Splines: hermite, catmull_rom
                                   # Easing: linear, ease_in_quad, ease_out_quad, ease_in_out_quad,
                                   #         ease_in_cubic, ease_out_cubic, ease_in_out_cubic,
                                   #         exponential, sine
    stops:                         # Position (stringified float) -> snapshot (index or name)
      "0.0": 0                     # Snapshot by index (0-based)
      "0.5": "Crunch"              # Or by name (case-insensitive prefix match)
      "1.0": "Heavy"               # Min separation: 1/127 (0.0079)
  - name: "Volume Swell"
    input_id: 1                    # Tweak1 encoder
    stops: ["Quiet", "Loud"]       # List format: auto-spaced evenly

Enabling and hooks

When we load a pedalboard with blend snapshots configured, we create a new snapshot for each . Whenever this snapshot is selected, we set it as the active_blend_mode in the handler. If we change / remove any of these blend snapshots, we automatically modify / delete them when we next switch to that pedalboard.

When the pedalboard is saved (and snapshots.json has been written, which requires saving the pedalboard, not just the snapshot), the generated snapshots are re-generated to sync constant values.

How blend mode works

We take over the chosen analog input by adding a callback to it that will override its default behaviour (e.g. sending a MIDI CC). We convert the value to a float (0..1) and use it to discover the stops that this value is contained within. Then, we discover which parameters differ between the two snapshots these stops are configured to use, and interpolate the parameters between them using websocket messages, e.g.

param_set /graph/StompBox_Fuzz/gain 0.654

Review checklist

• What do you think of creating these "special" snapshots?
• The analog callbacks are a bit hacky. I would love feedback on a better way to do this.

[rreichenbach]

Even without blend config defined, this is causing a regression for me. Changing the Snapshot via the Nav encoder, doesn't re-render the status for each plugin accordingly on the LCD.

It's possible that the code for this PR is in a weird state, but I have to say that I have reservations about this one.

It's cool, but I'm pretty sure less than 1% of users will ever use it. It's very advanced to set up and to understand.

If it didn't modify the regular/non-blend code path at all, I might be more keen on it, but it does. It adds code complexity, 7 new python files, and potential maintenance overhead.

For those who do use it, I'm imagining support calls (emails). There's a lot to get wrong in the config file.

So unless, you really think you need this. I'm suggesting against merging this.

UPDATE:
Actually... I was misunderstanding how this is configured (was thinking individual settings would need to get mapped, etc.) and didn't fully consider the power of this in a performance setting.

Forgive my skepticism above. If we can get this to work, I'm ok with the complexity hit. We need to figure out why it's messing with regular (non-blend) snapshot changes. My guess is that preset_change_plugin_update() isn't working like it used to.

[rreichenbach]

Looks good. thanks.