ptcrab 0.1.0

A pure-Rust alternative to the official pxtone library.
Documentation 
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/// Expression of pitch where 256 "key" increments = 1 semitone.
///
/// A value of 0 is equivalent to A<sub>(-4)</sub>; "key" is thus represented as the distance from
/// A<sub>(-4)</sub> in 1/256th-semitone increments. For example, A<sub>4</sub> is 96 semitones
/// above A<sub>(-4)</sub>, so it is represented using a key value of 96 × 256 = `0x6000`.
#[derive(Clone, Copy, Debug, PartialEq)]
#[repr(transparent)]
pub struct Key(i32);

impl Key {
    /// A<sub>4</sub> (440 Hz) tone.
    pub const A4: Self = Self(96 * 256);
    /// Middle C tone.
    pub const C4: Self = Self(87 * 256);
    /// A<sub>6</sub> tone (the default ptvoice inherent key).
    pub const A6: Self = Self::from_basic(0x2D00);

    /// Basic key reference value.
    pub const BASIC: i32 = 0x4500;

    /// Returns key value as [`i32`].
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A4.as_value(), 96 * 256);
    /// assert_eq!(Key::C4.as_value(), 87 * 256);
    /// ```
    pub const fn as_value(&self) -> i32 {
        self.0
    }

    /// Converts from key relative to A<sub>4</sub>.
    ///
    /// pxtone sometimes refers to key relative to A<sub>4</sub> instead of A<sub>(-4)</sub> so that
    /// commonly used pitches can be encoded into shorter sequences.
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A4, Key::from_a4_offset(0));
    /// assert_eq!(Key::C4, Key::from_a4_offset(-9 * 256));
    /// ```
    pub const fn from_a4_offset(a4_offset: i32) -> Self {
        Self(Self::A4.as_value() + a4_offset)
    }
    /// Returns key relative to A<sub>4</sub>.
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A4.as_a4_offset(),  0);
    /// assert_eq!(Key::C4.as_a4_offset(), -9 * 256);
    /// ```
    pub const fn as_a4_offset(&self) -> i32 {
        self.as_value() - Self::A4.as_value()
    }

    /// Converts from key relative to A<sub>6</sub> (the default ptvoice inherent key).
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A6, Key::from_a6_offset(0));
    /// assert_eq!(Key::A4, Key::from_a6_offset(-24 * 256));
    /// ```
    pub const fn from_a6_offset(a6_offset: i32) -> Self {
        Self(Self::A6.as_value() + a6_offset)
    }
    /// Returns key relative to A<sub>6</sub> (the default ptvoice inherent key).
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A6.as_a6_offset(), 0);
    /// assert_eq!(Key::A4.as_a6_offset(), -24 * 256);
    /// ```
    pub const fn as_a6_offset(&self) -> i32 {
        self.as_value() - Self::A6.as_value()
    }

    /// Converts from a "basic key" value.
    ///
    /// Samples that are not inherently pitched to A<sub>4</sub> can be corrected by modifying the
    /// voice's "basic key", which causes its key to be offset by a constant reference value
    /// ([`Key::BASIC`]) minus that voice's basic key value. As such, *increasing* the voice's
    /// basic key value will *decrease* its inherent pitch and vice versa.
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A4, Key::from_basic(Key::BASIC));
    /// assert_eq!(Key::C4, Key::from_basic(Key::BASIC + (9 * 256)));
    /// ```
    pub const fn from_basic(basic: i32) -> Self {
        Self::from_a4_offset(Self::BASIC - basic)
    }
    /// Returns "basic key" value.
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A4.as_basic(), Key::BASIC);
    /// assert_eq!(Key::C4.as_basic(), Key::BASIC + (9 * 256));
    /// ```
    pub const fn as_basic(&self) -> i32 {
        Self::BASIC - self.as_a4_offset()
    }

    /// Approximates key based on distance in semitones from A<sub>(-4)</sub>.
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A4, Key::approx_from_semis(96.));
    /// assert_eq!(Key::C4, Key::approx_from_semis(87.));
    /// ```
    pub fn approx_from_semis(semis: f32) -> Self {
        Self::from((semis * 256.) as i32)
    }
    /// Returns distance in semitones from A<sub>(-4)</sub>.
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A4.as_semis(), 96.);
    /// assert_eq!(Key::C4.as_semis(), 87.);
    /// ```
    pub fn as_semis(&self) -> f32 {
        (self.as_value() as f32) / 256.
    }

    /// Approximates key based on offset in semitones from A<sub>4</sub>.
    ///
    /// pxtone sometimes refers to key relative to A<sub>4</sub> instead of A<sub>(-4)</sub> so that
    /// commonly used pitches can be encoded into shorter sequences.
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A4, Key::approx_from_a4_semis(0.));
    /// assert_eq!(Key::C4, Key::approx_from_a4_semis(-9.));
    /// ```
    pub fn approx_from_a4_semis(a4_semis: f32) -> Self {
        Self::approx_from_semis(Self::A4.as_semis() + a4_semis)
    }
    /// Returns offset in semitones from A<sub>4</sub>.
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A4.as_a4_semis(),  0.);
    /// assert_eq!(Key::C4.as_a4_semis(), -9.);
    /// ```
    pub fn as_a4_semis(&self) -> f32 {
        (self.as_a4_offset() as f32) / 256.
    }

    /// Approximates key based on offset in semitones from A<sub>6</sub> (the default ptvoice
    /// inherent key).
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A6, Key::approx_from_a6_semis(0.));
    /// assert_eq!(Key::A4, Key::approx_from_a6_semis(-24.));
    /// ```
    pub fn approx_from_a6_semis(a6_semis: f32) -> Self {
        Self::approx_from_semis(Self::A6.as_semis() + a6_semis)
    }
    /// Returns offset in semitones from A<sub>6</sub> (the default ptvoice inherent key).
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A6.as_a6_semis(),  0.);
    /// assert_eq!(Key::A4.as_a6_semis(), -24.);
    /// ```
    pub fn as_a6_semis(&self) -> f32 {
        (self.as_a6_offset() as f32) / 256.
    }

    /// Converts from a "basic key" value in semitones.
    ///
    /// Samples that are not inherently pitched to A<sub>4</sub> can be corrected by modifying the
    /// voice's "basic key", which causes its key to be offset by a constant reference value
    /// ([`Self::BASIC`]) minus that voice's basic key value. As such, *increasing* the voice's
    /// basic key value will *decrease* its inherent pitch and vice versa.
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A4, Key::approx_from_basic_semis(69.));
    /// assert_eq!(Key::C4, Key::approx_from_basic_semis(78.));
    /// ```
    pub fn approx_from_basic_semis(basic_semis: f32) -> Self {
        Self::from_basic((basic_semis * 256.) as i32)
    }
    /// Returns "basic key" value in semitones.
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A4.as_basic_semis(), 69.);
    /// assert_eq!(Key::C4.as_basic_semis(), 69. + 9.);
    /// ```
    pub fn as_basic_semis(&self) -> f32 {
        (self.as_basic() as f32) / 256.
    }

    /// Approximates key from frequency in hertz.
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A4, Key::approx_from_hertz(440.));
    /// assert_eq!(Key::C4, Key::approx_from_hertz(261.62555));
    /// ```
    pub fn approx_from_hertz(frequency: f32) -> Self {
        Self::approx_from_a4_semis((frequency / Self::A4.as_hertz()).log2() * 12.)
    }
    /// Returns frequency in hertz.
    ///
    /// ```
    /// # use ptcrab::Key;
    /// assert_eq!(Key::A4.as_hertz(), 440.);
    /// assert_eq!(Key::C4.as_hertz(), 261.62555);
    /// ```
    pub fn as_hertz(&self) -> f32 {
        (self.as_a4_semis() / 12.).exp2() * 440.
    }
}

impl From<i32> for Key {
    fn from(value: i32) -> Self {
        Self(value)
    }
}

impl Default for Key {
    fn default() -> Self {
        Self::A4
    }
}