chromashift/
matrix.rs

1/// A 3x3 matrix of [`f64`], as used for linear colour space conversions.
2///
3/// Rows are the outer array: `Matrix3([row0, row1, row2])`.
4///
5/// ```
6/// # use chromashift::Matrix3;
7/// let m = Matrix3([[2.0, 0.0, 0.0], [0.0, 2.0, 0.0], [0.0, 0.0, 2.0]]);
8/// assert_eq!(m.transform([1.0, 2.0, 3.0]), [2.0, 4.0, 6.0]);
9/// ```
10#[derive(Debug, Clone, Copy, PartialEq)]
11pub struct Matrix3(pub [[f64; 3]; 3]);
12
13impl Matrix3 {
14	/// The matrix that leaves a vector unchanged.
15	pub const IDENTITY: Self = Self::diagonal([1.0, 1.0, 1.0]);
16
17	/// A matrix scaling each component independently.
18	pub const fn diagonal([x, y, z]: [f64; 3]) -> Self {
19		Self([[x, 0.0, 0.0], [0.0, y, 0.0], [0.0, 0.0, z]])
20	}
21
22	/// Applies this matrix to a column vector.
23	pub const fn transform(&self, [x, y, z]: [f64; 3]) -> [f64; 3] {
24		let Self(m) = self;
25		[
26			m[0][0] * x + m[0][1] * y + m[0][2] * z,
27			m[1][0] * x + m[1][1] * y + m[1][2] * z,
28			m[2][0] * x + m[2][1] * y + m[2][2] * z,
29		]
30	}
31
32	/// Multiplies two matrices, so that `a.then(b)` applies `a` first, then `b`.
33	pub const fn then(&self, next: &Self) -> Self {
34		let (Self(first), Self(second)) = (self, next);
35		let mut out = [[0.0; 3]; 3];
36		let mut row = 0;
37		while row < 3 {
38			let mut col = 0;
39			while col < 3 {
40				out[row][col] =
41					second[row][0] * first[0][col] + second[row][1] * first[1][col] + second[row][2] * first[2][col];
42				col += 1;
43			}
44			row += 1;
45		}
46		Self(out)
47	}
48
49	/// The inverse of this matrix.
50	///
51	/// Colour conversion matrices are always invertible; a singular matrix yields infinities rather than panicking.
52	///
53	/// ```
54	/// # use chromashift::{Matrix3, RgbSpace};
55	/// let roundtrip = RgbSpace::SRGB.to_xyz.inverse().then(&RgbSpace::SRGB.to_xyz);
56	/// assert!((roundtrip.0[0][0] - 1.0).abs() < 1e-12);
57	/// ```
58	pub const fn inverse(&self) -> Self {
59		let Self(m) = self;
60		let c00 = m[1][1] * m[2][2] - m[1][2] * m[2][1];
61		let c01 = m[1][2] * m[2][0] - m[1][0] * m[2][2];
62		let c02 = m[1][0] * m[2][1] - m[1][1] * m[2][0];
63		let det = m[0][0] * c00 + m[0][1] * c01 + m[0][2] * c02;
64		Self([
65			[c00 / det, (m[0][2] * m[2][1] - m[0][1] * m[2][2]) / det, (m[0][1] * m[1][2] - m[0][2] * m[1][1]) / det],
66			[c01 / det, (m[0][0] * m[2][2] - m[0][2] * m[2][0]) / det, (m[0][2] * m[1][0] - m[0][0] * m[1][2]) / det],
67			[c02 / det, (m[0][1] * m[2][0] - m[0][0] * m[2][1]) / det, (m[0][0] * m[1][1] - m[0][1] * m[1][0]) / det],
68		])
69	}
70}
chromashift/matrix.rs

chromashift/
matrix.rs
