Function curve

fn curve(
    ui: &mut Ui,
    f: &mut AudioFilter,
    key: (u64, usize),
    time: f64,
    palette: &Palette,
    state: &mut MixerState,
    g: &mut Gesture,
    n: usize,
) -> bool

EQ / pass-filter response plot: a labelled log-frequency + dB grid, the summed curve on top, and one draggable handle per band (X = frequency, Y = gain). The grabbed band is latched for the whole drag. Returns true when the drag changed a parameter.