restruct: 92e

src/device/clock.rs

@@ -0,0 +1,707 @@
+use crate::*;
+use ::std::sync::{Arc, RwLock, atomic::{AtomicUsize, Ordering::*}};
+use ::atomic_float::AtomicF64;
+use ::tengri::{draw::*, term::*};
+
+impl <T: AsRef<Clock>+AsMut<Clock>>                 HasClock     for T {}
+pub trait HasClock: AsRef<Clock> + AsMut<Clock> {
+    fn clock     (&self)     -> &Clock     { self.as_ref() }
+    fn clock_mut (&mut self) -> &mut Clock { self.as_mut() }
+}
+
+/// The source of time.
+///
+/// ```
+/// let clock = tek::Clock::default();
+/// ```
+#[derive(Clone, Default)] pub struct Clock {
+    /// JACK transport handle.
+    pub transport: Arc<Option<Transport>>,
+    /// Global temporal resolution (shared by [Moment] fields)
+    pub timebase:  Arc<Timebase>,
+    /// Current global sample and usec (monotonic from JACK clock)
+    pub global:    Arc<Moment>,
+    /// Global sample and usec at which playback started
+    pub started:   Arc<RwLock<Option<Moment>>>,
+    /// Playback offset (when playing not from start)
+    pub offset:    Arc<Moment>,
+    /// Current playhead position
+    pub playhead:  Arc<Moment>,
+    /// Note quantization factor
+    pub quant:     Arc<Quantize>,
+    /// Launch quantization factor
+    pub sync:      Arc<LaunchSync>,
+    /// Size of buffer in samples
+    pub chunk:     Arc<AtomicUsize>,
+    // Cache of formatted strings
+    pub view_cache: Arc<RwLock<ClockView>>,
+    /// For syncing the clock to an external source
+    #[cfg(feature = "port")] pub midi_in:   Arc<RwLock<Option<MidiInput>>>,
+    /// For syncing other devices to this clock
+    #[cfg(feature = "port")] pub midi_out:  Arc<RwLock<Option<MidiOutput>>>,
+    /// For emitting a metronome
+    #[cfg(feature = "port")] pub click_out: Arc<RwLock<Option<AudioOutput>>>,
+}
+
+/// Temporal resolutions: sample rate, tempo, MIDI pulses per quaver (beat)
+///
+/// ```
+/// let _ = tek::Timebase::default();
+/// ```
+#[derive(Debug, Clone)] pub struct Timebase {
+    /// Audio samples per second
+    pub sr:  SampleRate,
+    /// MIDI beats per minute
+    pub bpm: Bpm,
+    /// MIDI ticks per beat
+    pub ppq: Ppq,
+}
+
+/// Iterator that emits subsequent ticks within a range.
+///
+/// ```
+/// let iter = tek::Ticker::default();
+/// ```
+#[derive(Debug, Default)] pub struct Ticker {
+    pub spp:    f64,
+    pub sample: usize,
+    pub start:  usize,
+    pub end:    usize,
+}
+
+/// A point in time in all time scales (microsecond, sample, MIDI pulse)
+///
+/// ```
+/// let _ = tek::Moment::default();
+/// ```
+#[derive(Debug, Default, Clone)] pub struct Moment {
+    pub timebase: Arc<Timebase>,
+    /// Current time in microseconds
+    pub usec:   Microsecond,
+    /// Current time in audio samples
+    pub sample: SampleCount,
+    /// Current time in MIDI pulses
+    pub pulse:  Pulse,
+}
+
+///
+/// ```
+/// let _ = tek::Moment2::default();
+/// ```
+#[derive(Debug, Clone, Default)] pub enum Moment2 {
+    #[default] None,
+    Zero,
+    Usec(Microsecond),
+    Sample(SampleCount),
+    Pulse(Pulse),
+}
+
+/// MIDI resolution in PPQ (pulses per quarter note)
+///
+/// ```
+///
+/// ```
+#[derive(Debug, Default)] pub struct Ppq (pub(crate) AtomicF64);
+
+/// Timestamp in MIDI pulses
+///
+/// ```
+///
+/// ```
+#[derive(Debug, Default)] pub struct Pulse (pub(crate) AtomicF64);
+
+/// Tempo in beats per minute
+///
+/// ```
+///
+/// ```
+#[derive(Debug, Default)] pub struct Bpm (pub(crate) AtomicF64);
+
+/// Quantization setting for launching clips
+///
+/// ```
+///
+/// ```
+#[derive(Debug, Default)] pub struct LaunchSync (pub(crate) AtomicF64);
+
+/// Quantization setting for notes
+///
+/// ```
+///
+/// ```
+#[derive(Debug, Default)] pub struct Quantize (pub(crate) AtomicF64);
+
+/// Timestamp in audio samples
+///
+/// ```
+///
+/// ```
+#[derive(Debug, Default)] pub struct SampleCount (pub(crate) AtomicF64);
+
+/// Audio sample rate in Hz (samples per second)
+///
+/// ```
+///
+/// ```
+#[derive(Debug, Default)] pub struct SampleRate (pub(crate) AtomicF64);
+
+/// Timestamp in microseconds
+///
+/// ```
+///
+/// ```
+#[derive(Debug, Default)] pub struct Microsecond (pub(crate) AtomicF64);
+
+/// A unit of time, represented as an atomic 64-bit float.
+///
+/// According to https://stackoverflow.com/a/873367, as per IEEE754,
+/// every integer between 1 and 2^53 can be represented exactly.
+/// This should mean that, even at 192kHz sampling rate, over 1 year of audio
+/// can be clocked in microseconds with f64 without losing precision.
+pub trait TimeUnit: InteriorMutable<f64> {}
+
+/// Contains memoized renders of clock values.
+///
+/// Performance optimization.
+#[derive(Debug)] pub struct ClockView {
+    pub sr:   Memo<Option<(bool, f64)>, String>,
+    pub buf:  Memo<Option<f64>, String>,
+    pub lat:  Memo<Option<f64>, String>,
+    pub bpm:  Memo<Option<f64>, String>,
+    pub beat: Memo<Option<f64>, String>,
+    pub time: Memo<Option<f64>, String>,
+}
+
+/// FIXME: remove this and use PPQ from timebase everywhere:
+pub const PPQ: usize = 96;
+
+/// (pulses, name), assuming 96 PPQ
+pub const NOTE_DURATIONS: [(usize, &str);26] = [
+    (1,    "1/384"), (2,    "1/192"),
+    (3,    "1/128"), (4,    "1/96"),
+    (6,    "1/64"),  (8,    "1/48"),
+    (12,   "1/32"),  (16,   "1/24"),
+    (24,   "1/16"),  (32,   "1/12"),
+    (48,   "1/8"),   (64,   "1/6"),
+    (96,   "1/4"),   (128,  "1/3"),
+    (192,  "1/2"),   (256,  "2/3"),
+    (384,  "1/1"),   (512,  "4/3"),
+    (576,  "3/2"),   (768,  "2/1"),
+    (1152, "3/1"),   (1536, "4/1"),
+    (2304, "6/1"),   (3072, "8/1"),
+    (3456, "9/1"),   (6144, "16/1"),
+];
+
+pub const NOTE_NAMES: [&str; 128] = [
+    "C0",  "C#0",  "D0",  "D#0",  "E0",  "F0",  "F#0",  "G0", "G#0", "A0", "A#0", "B0",
+    "C1",  "C#1",  "D1",  "D#1",  "E1",  "F1",  "F#1",  "G1", "G#1", "A1", "A#1", "B1",
+    "C2",  "C#2",  "D2",  "D#2",  "E2",  "F2",  "F#2",  "G2", "G#2", "A2", "A#2", "B2",
+    "C3",  "C#3",  "D3",  "D#3",  "E3",  "F3",  "F#3",  "G3", "G#3", "A3", "A#3", "B3",
+    "C4",  "C#4",  "D4",  "D#4",  "E4",  "F4",  "F#4",  "G4", "G#4", "A4", "A#4", "B4",
+    "C5",  "C#5",  "D5",  "D#5",  "E5",  "F5",  "F#5",  "G5", "G#5", "A5", "A#5", "B5",
+    "C6",  "C#6",  "D6",  "D#6",  "E6",  "F6",  "F#6",  "G6", "G#6", "A6", "A#6", "B6",
+    "C7",  "C#7",  "D7",  "D#7",  "E7",  "F7",  "F#7",  "G7", "G#7", "A7", "A#7", "B7",
+    "C8",  "C#8",  "D8",  "D#8",  "E8",  "F8",  "F#8",  "G8", "G#8", "A8", "A#8", "B8",
+    "C9",  "C#9",  "D9",  "D#9",  "E9",  "F9",  "F#9",  "G9", "G#9", "A9", "A#9", "B9",
+    "C10", "C#10", "D10", "D#10", "E10", "F10", "F#10", "G10",
+];
+
+pub const DEFAULT_PPQ: f64 = 96.0;
+
+def_command!(ClockCommand: |clock: Clock| {
+    SeekUsec   { usec:   f64 } => {
+        clock.playhead.update_from_usec(*usec); Ok(None) },
+    SeekSample { sample: f64 } => {
+        clock.playhead.update_from_sample(*sample); Ok(None) },
+    SeekPulse  { pulse:  f64 } => {
+        clock.playhead.update_from_pulse(*pulse); Ok(None) },
+    SetBpm     { bpm:    f64 } => Ok(Some(
+        Self::SetBpm { bpm: clock.timebase().bpm.set(*bpm) })),
+    SetQuant   { quant:  f64 } => Ok(Some(
+        Self::SetQuant { quant: clock.quant.set(*quant) })),
+    SetSync    { sync:   f64 } => Ok(Some(
+        Self::SetSync { sync: clock.sync.set(*sync) })),
+
+    Play  { position: Option<u32> } => {
+        clock.play_from(*position)?; Ok(None) /* TODO Some(Pause(previousPosition)) */ },
+    Pause { position: Option<u32> } => {
+        clock.pause_at(*position)?; Ok(None) },
+
+    TogglePlayback { position: u32 } => Ok(if clock.is_rolling() {
+        clock.pause_at(Some(*position))?; None
+    } else {
+        clock.play_from(Some(*position))?; None
+    }),
+});
+
+impl Moment {
+    pub fn zero (timebase: &Arc<Timebase>) -> Self {
+        Self { usec: 0.into(), sample: 0.into(), pulse: 0.into(), timebase: timebase.clone() }
+    }
+    pub fn from_usec (timebase: &Arc<Timebase>, usec: f64) -> Self {
+        Self {
+            usec:     usec.into(),
+            sample:   timebase.sr.usecs_to_sample(usec).into(),
+            pulse:    timebase.usecs_to_pulse(usec).into(),
+            timebase: timebase.clone(),
+        }
+    }
+    pub fn from_sample (timebase: &Arc<Timebase>, sample: f64) -> Self {
+        Self {
+            sample:   sample.into(),
+            usec:     timebase.sr.samples_to_usec(sample).into(),
+            pulse:    timebase.samples_to_pulse(sample).into(),
+            timebase: timebase.clone(),
+        }
+    }
+    pub fn from_pulse (timebase: &Arc<Timebase>, pulse: f64) -> Self {
+        Self {
+            pulse:    pulse.into(),
+            sample:   timebase.pulses_to_sample(pulse).into(),
+            usec:     timebase.pulses_to_usec(pulse).into(),
+            timebase: timebase.clone(),
+        }
+    }
+    #[inline] pub fn update_from_usec (&self, usec: f64) {
+        self.usec.set(usec);
+        self.pulse.set(self.timebase.usecs_to_pulse(usec));
+        self.sample.set(self.timebase.sr.usecs_to_sample(usec));
+    }
+    #[inline] pub fn update_from_sample (&self, sample: f64) {
+        self.usec.set(self.timebase.sr.samples_to_usec(sample));
+        self.pulse.set(self.timebase.samples_to_pulse(sample));
+        self.sample.set(sample);
+    }
+    #[inline] pub fn update_from_pulse (&self, pulse: f64) {
+        self.usec.set(self.timebase.pulses_to_usec(pulse));
+        self.pulse.set(pulse);
+        self.sample.set(self.timebase.pulses_to_sample(pulse));
+    }
+    #[inline] pub fn format_beat (&self) -> Arc<str> {
+        self.timebase.format_beats_1(self.pulse.get()).into()
+    }
+}
+impl LaunchSync {
+    pub fn next (&self) -> f64 {
+        note_duration_next(self.get() as usize) as f64
+    }
+    pub fn prev (&self) -> f64 {
+        note_duration_prev(self.get() as usize) as f64
+    }
+}
+impl Quantize {
+    pub fn next (&self) -> f64 {
+        note_duration_next(self.get() as usize) as f64
+    }
+    pub fn prev (&self) -> f64 {
+        note_duration_prev(self.get() as usize) as f64
+    }
+}
+impl Timebase {
+    /// Specify sample rate, BPM and PPQ
+    pub fn new (
+        s: impl Into<SampleRate>,
+        b: impl Into<Bpm>,
+        p: impl Into<Ppq>
+    ) -> Self {
+        Self { sr: s.into(), bpm: b.into(), ppq: p.into() }
+    }
+    /// Iterate over ticks between start and end.
+    #[inline] pub fn pulses_between_samples (&self, start: usize, end: usize) -> Ticker {
+        Ticker { spp: self.samples_per_pulse(), sample: start, start, end }
+    }
+    /// Return the duration fo a beat in microseconds
+    #[inline] pub fn usec_per_beat (&self) -> f64 { 60_000_000f64 / self.bpm.get() }
+    /// Return the number of beats in a second
+    #[inline] pub fn beat_per_second (&self) -> f64 { self.bpm.get() / 60f64 }
+    /// Return the number of microseconds corresponding to a note of the given duration
+    #[inline] pub fn note_to_usec (&self, (num, den): (f64, f64)) -> f64 {
+        4.0 * self.usec_per_beat() * num / den
+    }
+    /// Return duration of a pulse in microseconds (BPM-dependent)
+    #[inline] pub fn pulse_per_usec (&self) -> f64 { self.ppq.get() / self.usec_per_beat() }
+    /// Return duration of a pulse in microseconds (BPM-dependent)
+    #[inline] pub fn usec_per_pulse (&self) -> f64 { self.usec_per_beat() / self.ppq.get() }
+    /// Return number of pulses to which a number of microseconds corresponds (BPM-dependent)
+    #[inline] pub fn usecs_to_pulse (&self, usec: f64) -> f64 { usec * self.pulse_per_usec() }
+    /// Convert a number of pulses to a sample number (SR- and BPM-dependent)
+    #[inline] pub fn pulses_to_usec (&self, pulse: f64) -> f64 { pulse / self.usec_per_pulse() }
+    /// Return number of pulses in a second (BPM-dependent)
+    #[inline] pub fn pulses_per_second (&self) -> f64 { self.beat_per_second() * self.ppq.get() }
+    /// Return fraction of a pulse to which a sample corresponds (SR- and BPM-dependent)
+    #[inline] pub fn pulses_per_sample (&self) -> f64 {
+        self.usec_per_pulse() / self.sr.usec_per_sample()
+    }
+    /// Return number of samples in a pulse (SR- and BPM-dependent)
+    #[inline] pub fn samples_per_pulse (&self) -> f64 {
+        self.sr.get() / self.pulses_per_second()
+    }
+    /// Convert a number of pulses to a sample number (SR- and BPM-dependent)
+    #[inline] pub fn pulses_to_sample (&self, p: f64) -> f64 {
+        self.pulses_per_sample() * p
+    }
+    /// Convert a number of samples to a pulse number (SR- and BPM-dependent)
+    #[inline] pub fn samples_to_pulse (&self, s: f64) -> f64 {
+        s / self.pulses_per_sample()
+    }
+    /// Return the number of samples corresponding to a note of the given duration
+    #[inline] pub fn note_to_samples (&self, note: (f64, f64)) -> f64 {
+        self.usec_to_sample(self.note_to_usec(note))
+    }
+    /// Return the number of samples corresponding to the given number of microseconds
+    #[inline] pub fn usec_to_sample (&self, usec: f64) -> f64 {
+        usec * self.sr.get() / 1000f64
+    }
+    /// Return the quantized position of a moment in time given a step
+    #[inline] pub fn quantize (&self, step: (f64, f64), time: f64) -> (f64, f64) {
+        let step = self.note_to_usec(step);
+        (time / step, time % step)
+    }
+    /// Quantize a collection of events
+    #[inline] pub fn quantize_into <E: Iterator<Item=(f64, f64)> + Sized, T> (
+        &self, step: (f64, f64), events: E
+    ) -> Vec<(f64, f64)> {
+        events.map(|(time, event)|(self.quantize(step, time).0, event)).collect()
+    }
+    /// Format a number of pulses into Beat.Bar.Pulse starting from 0
+    #[inline] pub fn format_beats_0 (&self, pulse: f64) -> Arc<str> {
+        let pulse = pulse as usize;
+        let ppq   = self.ppq.get() as usize;
+        let (beats, pulses) = if ppq > 0 { (pulse / ppq, pulse % ppq) } else { (0, 0) };
+        format!("{}.{}.{pulses:02}", beats / 4, beats % 4).into()
+    }
+    /// Format a number of pulses into Beat.Bar starting from 0
+    #[inline] pub fn format_beats_0_short (&self, pulse: f64) -> Arc<str> {
+        let pulse = pulse as usize;
+        let ppq   = self.ppq.get() as usize;
+        let beats = if ppq > 0 { pulse / ppq } else { 0 };
+        format!("{}.{}", beats / 4, beats % 4).into()
+    }
+    /// Format a number of pulses into Beat.Bar.Pulse starting from 1
+    #[inline] pub fn format_beats_1 (&self, pulse: f64) -> Arc<str> {
+        let mut string = String::with_capacity(16);
+        self.format_beats_1_to(&mut string, pulse).expect("failed to format {pulse} into beat");
+        string.into()
+    }
+    /// Format a number of pulses into Beat.Bar.Pulse starting from 1
+    #[inline] pub fn format_beats_1_to (&self, w: &mut impl std::fmt::Write, pulse: f64) -> Result<(), std::fmt::Error> {
+        let pulse = pulse as usize;
+        let ppq   = self.ppq.get() as usize;
+        let (beats, pulses) = if ppq > 0 { (pulse / ppq, pulse % ppq) } else { (0, 0) };
+        write!(w, "{}.{}.{pulses:02}", beats / 4 + 1, beats % 4 + 1)
+    }
+    /// Format a number of pulses into Beat.Bar.Pulse starting from 1
+    #[inline] pub fn format_beats_1_short (&self, pulse: f64) -> Arc<str> {
+        let pulse = pulse as usize;
+        let ppq   = self.ppq.get() as usize;
+        let beats = if ppq > 0 { pulse / ppq } else { 0 };
+        format!("{}.{}", beats / 4 + 1, beats % 4 + 1).into()
+    }
+}
+impl SampleRate {
+    /// Return the duration of a sample in microseconds (floating)
+    #[inline] pub fn usec_per_sample (&self) -> f64 {
+        1_000_000f64 / self.get()
+    }
+    /// Return the duration of a sample in microseconds (floating)
+    #[inline] pub fn sample_per_usec (&self) -> f64 {
+        self.get() / 1_000_000f64
+    }
+    /// Convert a number of samples to microseconds (floating)
+    #[inline] pub fn samples_to_usec (&self, samples: f64) -> f64 {
+        self.usec_per_sample() * samples
+    }
+    /// Convert a number of microseconds to samples (floating)
+    #[inline] pub fn usecs_to_sample (&self, usecs:   f64) -> f64 {
+        self.sample_per_usec() * usecs
+    }
+}
+impl Microsecond {
+    #[inline] pub fn format_msu (&self) -> Arc<str> {
+        let usecs              = self.get() as usize;
+        let (seconds, msecs)   = (usecs / 1000000, usecs / 1000 % 1000);
+        let (minutes, seconds) = (seconds / 60, seconds % 60);
+        format!("{minutes}:{seconds:02}:{msecs:03}").into()
+    }
+}
+
+/// Define and implement a unit of time
+#[macro_export] macro_rules! impl_time_unit {
+    ($T:ident) => {
+        impl Gettable<f64> for $T {
+            fn get (&self) -> f64 { self.0.load(Relaxed) }
+        }
+        impl InteriorMutable<f64> for $T {
+            fn set (&self, value: f64) -> f64 {
+                let old = self.get();
+                self.0.store(value, Relaxed);
+                old
+            }
+        }
+        impl TimeUnit for $T {}
+        impl_op!($T, Add, add, |a, b|{a + b});
+        impl_op!($T, Sub, sub, |a, b|{a - b});
+        impl_op!($T, Mul, mul, |a, b|{a * b});
+        impl_op!($T, Div, div, |a, b|{a / b});
+        impl_op!($T, Rem, rem, |a, b|{a % b});
+        impl From<f64>   for $T    { fn from (value: f64)   -> Self { Self(value.into()) } }
+        impl From<usize> for $T    { fn from (value: usize) -> Self { Self((value as f64).into()) } }
+        impl From<$T>    for f64   { fn from (value: $T)    -> Self { value.get() } }
+        impl From<$T>    for usize { fn from (value: $T)    -> Self { value.get() as usize } }
+        impl From<&$T>   for f64   { fn from (value: &$T)   -> Self { value.get() } }
+        impl From<&$T>   for usize { fn from (value: &$T)   -> Self { value.get() as usize } }
+        impl Clone for $T { fn clone (&self) -> Self { Self(self.get().into()) } }
+    }
+}
+
+impl std::fmt::Debug for Clock {
+    fn fmt (&self, f: &mut Formatter<'_>) -> std::result::Result<(), std::fmt::Error> {
+        f.debug_struct("Clock")
+            .field("timebase", &self.timebase)
+            .field("chunk",    &self.chunk)
+            .field("quant",    &self.quant)
+            .field("sync",     &self.sync)
+            .field("global",   &self.global)
+            .field("playhead", &self.playhead)
+            .field("started",  &self.started)
+            .finish()
+    }
+}
+impl Clock {
+    pub fn new (jack: &Jack<'static>, bpm: Option<f64>) -> Usually<Self> {
+        let (chunk, transport) = jack.with_client(|c|(c.buffer_size(), c.transport()));
+        let timebase = Arc::new(Timebase::default());
+        let clock = Self {
+            quant:     Arc::new(24.into()),
+            sync:      Arc::new(384.into()),
+            transport: Arc::new(Some(transport)),
+            chunk:     Arc::new((chunk as usize).into()),
+            global:    Arc::new(Moment::zero(&timebase)),
+            playhead:  Arc::new(Moment::zero(&timebase)),
+            offset:    Arc::new(Moment::zero(&timebase)),
+            started:   RwLock::new(None).into(),
+            timebase,
+            midi_in:   Arc::new(RwLock::new(Some(MidiInput::new(jack,   &"M/clock", &[])?))),
+            midi_out:  Arc::new(RwLock::new(Some(MidiOutput::new(jack,  &"clock/M", &[])?))),
+            click_out: Arc::new(RwLock::new(Some(AudioOutput::new(jack, &"click",   &[])?))),
+            ..Default::default()
+        };
+        if let Some(bpm) = bpm {
+            clock.timebase.bpm.set(bpm);
+        }
+        Ok(clock)
+    }
+    pub fn timebase (&self) -> &Arc<Timebase> {
+        &self.timebase
+    }
+    /// Current sample rate
+    pub fn sr (&self) -> &SampleRate {
+        &self.timebase.sr
+    }
+    /// Current tempo
+    pub fn bpm (&self) -> &Bpm {
+        &self.timebase.bpm
+    }
+    /// Current MIDI resolution
+    pub fn ppq (&self) -> &Ppq {
+        &self.timebase.ppq
+    }
+    /// Next pulse that matches launch sync (for phrase switchover)
+    pub fn next_launch_pulse (&self) -> usize {
+        let sync  = self.sync.get() as usize;
+        let pulse = self.playhead.pulse.get() as usize;
+        if pulse % sync == 0 {
+            pulse
+        } else {
+            (pulse / sync + 1) * sync
+        }
+    }
+    /// Start playing, optionally seeking to a given location beforehand
+    pub fn play_from (&self, start: Option<u32>) -> Usually<()> {
+        if let Some(transport) = self.transport.as_ref() {
+            if let Some(start) = start {
+                transport.locate(start)?;
+            }
+            transport.start()?;
+        }
+        Ok(())
+    }
+    /// Pause, optionally seeking to a given location afterwards
+    pub fn pause_at (&self, pause: Option<u32>) -> Usually<()> {
+        if let Some(transport) = self.transport.as_ref() {
+            transport.stop()?;
+            if let Some(pause) = pause {
+                transport.locate(pause)?;
+            }
+        }
+        Ok(())
+    }
+    /// Is currently paused?
+    pub fn is_stopped (&self) -> bool {
+        self.started.read().unwrap().is_none()
+    }
+    /// Is currently playing?
+    pub fn is_rolling (&self) -> bool {
+        self.started.read().unwrap().is_some()
+    }
+    /// Update chunk size
+    pub fn set_chunk (&self, n_frames: usize) {
+        self.chunk.store(n_frames, Relaxed);
+    }
+    pub fn update_from_scope (&self, scope: &ProcessScope) -> Usually<()> {
+        // Store buffer length
+        self.set_chunk(scope.n_frames() as usize);
+
+        // Store reported global frame and usec
+        let CycleTimes { current_frames, current_usecs, .. } = scope.cycle_times()?;
+        self.global.sample.set(current_frames as f64);
+        self.global.usec.set(current_usecs as f64);
+
+        let mut started = self.started.write().unwrap();
+
+        // If transport has just started or just stopped,
+        // update starting point:
+        if let Some(transport) = self.transport.as_ref() {
+            match (transport.query_state()?, started.as_ref()) {
+                (TransportState::Rolling, None) => {
+                    let moment = Moment::zero(&self.timebase);
+                    moment.sample.set(current_frames as f64);
+                    moment.usec.set(current_usecs as f64);
+                    *started = Some(moment);
+                },
+                (TransportState::Stopped, Some(_)) => {
+                    *started = None;
+                },
+                _ => {}
+            };
+        }
+
+        self.playhead.update_from_sample(started.as_ref()
+            .map(|started|current_frames as f64 - started.sample.get())
+            .unwrap_or(0.));
+
+        Ok(())
+    }
+
+    pub fn bbt (&self) -> PositionBBT {
+        let pulse = self.playhead.pulse.get() as i32;
+        let ppq   = self.timebase.ppq.get() as i32;
+        let bpm   = self.timebase.bpm.get();
+        let bar   = (pulse / ppq) / 4;
+        PositionBBT {
+            bar:              1 + bar,
+            beat:             1 + (pulse / ppq) % 4,
+            tick:             (pulse % ppq),
+            bar_start_tick:   (bar * 4 * ppq) as f64,
+            beat_type:        4.,
+            beats_per_bar:    4.,
+            beats_per_minute: bpm,
+            ticks_per_beat:   ppq as f64
+        }
+    }
+
+    pub fn next_launch_instant (&self) -> Moment {
+        Moment::from_pulse(self.timebase(), self.next_launch_pulse() as f64)
+    }
+
+    /// Get index of first sample to populate.
+    ///
+    /// Greater than 0 means that the first pulse of the clip
+    /// falls somewhere in the middle of the chunk.
+    pub fn get_sample_offset (&self, scope: &ProcessScope, started: &Moment) -> usize{
+        (scope.last_frame_time() as usize).saturating_sub(
+            started.sample.get() as usize +
+            self.started.read().unwrap().as_ref().unwrap().sample.get() as usize
+        )
+    }
+
+    // Get iterator that emits sample paired with pulse.
+    //
+    // * Sample: index into output buffer at which to write MIDI event
+    // * Pulse: index into clip from which to take the MIDI event
+    //
+    // Emitted for each sample of the output buffer that corresponds to a MIDI pulse.
+    pub fn get_pulses (&self, scope: &ProcessScope, offset: usize) -> Ticker {
+        self.timebase().pulses_between_samples(offset, offset + scope.n_frames() as usize)
+    }
+}
+impl Clock {
+    fn _todo_provide_u32 (&self) -> u32 {
+        todo!()
+    }
+    fn _todo_provide_opt_u32 (&self) -> Option<u32> {
+        todo!()
+    }
+    fn _todo_provide_f64 (&self) -> f64 {
+        todo!()
+    }
+}
+impl<T: HasClock> Act<T> for ClockCommand {
+    fn act (&self, state: &mut T) -> Perhaps<Self> {
+        self.act(state.clock_mut()) // awesome
+    }
+}
+impl ClockView {
+    pub const BEAT_EMPTY: &'static str = "-.-.--";
+    pub const TIME_EMPTY: &'static str = "-.---s";
+    pub const BPM_EMPTY:  &'static str = "---.---";
+    pub fn update_clock (cache: &Arc<RwLock<Self>>, clock: &Clock, compact: bool) {
+        let rate  = clock.timebase.sr.get();
+        let chunk = clock.chunk.load(Relaxed) as f64;
+        let lat   = chunk / rate * 1000.;
+        let delta = |start: &Moment|clock.global.usec.get() - start.usec.get();
+        let mut cache = cache.write().unwrap();
+        cache.buf.update(Some(chunk), rewrite!(buf, "{chunk}"));
+        cache.lat.update(Some(lat),   rewrite!(buf, "{lat:.1}ms"));
+        cache.sr.update(Some((compact, rate)), |buf,_,_|{
+            buf.clear();
+            if compact {
+                write!(buf, "{:.1}kHz", rate / 1000.)
+            } else {
+                write!(buf, "{:.0}Hz", rate)
+            }
+        });
+        if let Some(now) = clock.started.read().unwrap().as_ref().map(delta) {
+            let pulse = clock.timebase.usecs_to_pulse(now);
+            let time  = now/1000000.;
+            let bpm   = clock.timebase.bpm.get();
+            cache.beat.update(Some(pulse), |buf, _, _|{
+                buf.clear();
+                clock.timebase.format_beats_1_to(buf, pulse)
+            });
+            cache.time.update(Some(time), rewrite!(buf, "{:.3}s", time));
+            cache.bpm.update(Some(bpm),   rewrite!(buf, "{:.3}",  bpm));
+        } else {
+            cache.beat.update(None, rewrite!(buf, "{}", ClockView::BEAT_EMPTY));
+            cache.time.update(None, rewrite!(buf, "{}", ClockView::TIME_EMPTY));
+            cache.bpm.update(None,  rewrite!(buf, "{}", ClockView::BPM_EMPTY));
+        }
+    }
+}
+impl_default!(ClockView: {
+    let mut beat = String::with_capacity(16);
+    let _ = write!(beat, "{}", Self::BEAT_EMPTY);
+    let mut time = String::with_capacity(16);
+    let _ = write!(time, "{}", Self::TIME_EMPTY);
+    let mut bpm  = String::with_capacity(16);
+    let _ = write!(bpm,  "{}", Self::BPM_EMPTY);
+    Self {
+        beat: Memo::new(None, beat),
+        time: Memo::new(None, time),
+        bpm:  Memo::new(None, bpm),
+        sr:   Memo::new(None, String::with_capacity(16)),
+        buf:  Memo::new(None, String::with_capacity(16)),
+        lat:  Memo::new(None, String::with_capacity(16)),
+    }
+});
+
+#[cfg(feature = "clock")] impl_has!(Clock: |self: Track|self.sequencer.clock);
+impl_default!(Timebase:       Self::new(48000f64, 150f64, DEFAULT_PPQ));
+impl_time_unit!(SampleCount);
+impl_time_unit!(SampleRate);
+impl_time_unit!(Microsecond);
+impl_time_unit!(Quantize);
+impl_time_unit!(Ppq);
+impl_time_unit!(Pulse);
+impl_time_unit!(Bpm);
+impl_time_unit!(LaunchSync);