// Acid bass, the 303 contract: one voice per line (play it mono and use
// legato notes for slides), saw or square into a resonant ladder whose
// envelope decays per note; accents (velocity above 0.8) open the filter
// further, decay faster and play louder; slides glide the pitch.
let cutoff = param(380, 30, 8000)
let res = param(0.72, 0, 1)
let env_mod = param(0.6, 0, 1)
let decay = param(0.25, 0.02, 2)
let accent = param(0.7, 0, 1)
let slide = param(0.06, 0.005, 0.5)
let square = param(0, 0, 1)
let drive = param(1.6, 1, 8)
let gain = param(0.5, 0, 1)

var ph = 0.0
var hz = 0.0
var env = 0.0
var acc = 0.0
var amp = 0.0
var slide_k = 0.0
var lad = Ladder{}
var dc = DcBlock{}

fn block() {
    let sweep = cutoff * exp2(env_mod * 6.0 * env + acc * accent * 2.0)
    ladder_set(lad, sweep, res)
    slide_k = 1.0 - exp(-5.0 / (slide * sample_rate))
}

fn voice() {
    if trigger {
        hz = freq
        env = 1.0
        acc = if velocity > 0.8 { 1.0 } else { 0.0 }
    }
    // Slide: legato notes move `freq`; `slide` is the time to get there.
    hz = hz + (freq - hz) * slide_k
    env = env * exp(-5.0 / (decay * (1.0 - 0.5 * acc) * sample_rate))
    let dt = hz / sample_rate
    ph = advance(ph, dt)
    let osc = if square > 0.5 { pulse_blep(ph, dt, 0.5) } else { saw_blep(ph, dt) }
    let y = ladder(lad, osc * drive * 0.5)
    if gate > 0.0 {
        amp = min(amp + 400.0 / sample_rate, 1.0)
    } else {
        amp = amp * exp(-1.0 / (0.012 * sample_rate))
        if amp < 0.00001 {
            stop()
        }
    }
    dc_block(dc, soft_clip(y * drive)) * amp * gain * (1.0 + 0.4 * acc * accent)
}