music21_rs/scale/
diatonicscale.rs

1use crate::{chord::Chord, defaults::IntegerType, error::Result, pitch::Pitch};
2
3use super::concretescale::ConcreteScale;
4
5#[derive(Clone, Debug)]
6/// A diatonic scale realized from a tonic, key signature, and mode.
7#[must_use]
8pub struct DiatonicScale {
9    concrete: ConcreteScale,
10    mode: String,
11}
12
13impl DiatonicScale {
14    pub(crate) fn new(tonic: Pitch, sharps: IntegerType, mode: &str) -> Self {
15        Self {
16            concrete: ConcreteScale::new(tonic, sharps),
17            mode: mode.to_string(),
18        }
19    }
20
21    /// Returns the scale mode.
22    pub fn mode(&self) -> &str {
23        &self.mode
24    }
25
26    /// Returns the tonic pitch.
27    pub fn tonic(&self) -> &Pitch {
28        self.concrete.tonic()
29    }
30
31    /// Returns the pitch at a one-based scale degree.
32    pub fn pitch_from_degree(&self, degree: usize) -> Result<Pitch> {
33        self.concrete.pitch_from_degree(degree)
34    }
35
36    /// Returns pitches from degree 1 through the octave.
37    pub fn pitches(&self) -> Result<Vec<Pitch>> {
38        self.concrete.pitches()
39    }
40
41    /// Builds a diatonic triad from a one-based degree.
42    pub fn triad_from_degree(&self, degree: usize) -> Result<Chord> {
43        let notes = vec![
44            self.pitch_from_degree(degree)?,
45            self.pitch_from_degree(degree + 2)?,
46            self.pitch_from_degree(degree + 4)?,
47        ];
48        Chord::new(notes.as_slice())
49    }
50
51    /// Builds a diatonic seventh chord from a one-based degree.
52    pub fn seventh_chord_from_degree(&self, degree: usize) -> Result<Chord> {
53        let notes = vec![
54            self.pitch_from_degree(degree)?,
55            self.pitch_from_degree(degree + 2)?,
56            self.pitch_from_degree(degree + 4)?,
57            self.pitch_from_degree(degree + 6)?,
58        ];
59        Chord::new(notes.as_slice())
60    }
61}
62
63#[cfg(test)]
64mod tests {
65    use super::*;
66
67    fn pitch(name: &str) -> Pitch {
68        Pitch::from_name(name).expect("valid pitch")
69    }
70
71    #[test]
72    fn diatonic_scale_degree_lookup() {
73        let scale = DiatonicScale::new(pitch("A4"), 0, "minor");
74        assert_eq!(scale.pitch_from_degree(1).unwrap().name_with_octave(), "A4");
75        assert_eq!(scale.pitch_from_degree(3).unwrap().name_with_octave(), "C5");
76        assert_eq!(scale.pitch_from_degree(7).unwrap().name_with_octave(), "G5");
77    }
78
79    #[test]
80    fn diatonic_scale_degree_chords() {
81        let scale = DiatonicScale::new(pitch("C4"), 0, "major");
82        assert_eq!(
83            scale.triad_from_degree(1).unwrap().pitched_common_name(),
84            "C-major triad"
85        );
86        assert_eq!(
87            scale
88                .seventh_chord_from_degree(5)
89                .unwrap()
90                .pitched_common_name(),
91            "G-dominant seventh chord"
92        );
93    }
94}
music21_rs/scale/diatonicscale.rs

music21_rs/scale/
diatonicscale.rs
