lighthouse_protocol/utils/
rotation.rs

1use std::ops::{Add, Mul, Neg};
2
3use rand::{thread_rng, Rng};
4
5use crate::Vec2;
6
7use super::{Unity, Zero};
8
9// TODO: Rename this to Mat2?
10
11/// An 2D rotation that is representable using an integer matrix.
12#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
13pub struct Rotation<T> {
14    /// The integer matrix representing the corresponding linear transformation.
15    matrix: [T; 4],
16}
17
18impl<T> Rotation<T> where T: Zero + Unity + Neg<Output = T> {
19    /// The identity rotation.
20    pub const IDENTITY: Self = Self::new([
21        T::ONE,  T::ZERO,
22        T::ZERO, T::ONE,
23    ]);
24    /// The rotation by 90° clockwise.
25    pub const CW_90: Self = Self::new([
26         T::ZERO, T::NEG_ONE,
27         T::ONE,  T::ZERO,
28    ]);
29    /// The rotation by 180° clockwise or counter-clockwise.
30    pub const CW_180: Self = Self::new([
31        T::NEG_ONE, T::ZERO,
32        T::ZERO,    T::NEG_ONE,
33    ]);
34    /// The rotation by 270° clockwise (or 90° counter-clockwise).
35    pub const CW_270: Self = Self::new([
36        T::ZERO,    T::ONE,
37        T::NEG_ONE, T::ZERO,
38    ]);
39
40    /// Creates a new rotation from the given matrix.
41    pub const fn new(matrix: [T; 4]) -> Self {
42        Self { matrix }
43    }
44
45    /// Randomly one of the four cardinal rotations with the given rng.
46    pub fn random_cardinal_with(rng: &mut impl Rng) -> Self {
47        match rng.gen_range(0..4) {
48            0 => Self::IDENTITY,
49            1 => Self::CW_90,
50            2 => Self::CW_180,
51            3 => Self::CW_270,
52            _ => unreachable!(),
53        }
54    }
55
56    /// Randomly one of the four cardinal rotations with the thread-local rng.
57    pub fn random_cardinal() -> Self {
58        Self::random_cardinal_with(&mut thread_rng())
59    }
60}
61
62impl<T> Mul<Self> for Rotation<T> where T: Zero + Unity + Neg<Output = T> + Add<Output = T> + Mul<Output = T> + Copy {
63    type Output = Self;
64
65    fn mul(self, rhs: Self) -> Self {
66        // Standard 2x2 matrix multiplication
67        Self::new([
68            self.matrix[0] * rhs.matrix[0] + self.matrix[1] * rhs.matrix[2],
69            self.matrix[0] * rhs.matrix[1] + self.matrix[1] * rhs.matrix[3],
70            self.matrix[2] * rhs.matrix[0] + self.matrix[3] * rhs.matrix[2],
71            self.matrix[2] * rhs.matrix[1] + self.matrix[3] * rhs.matrix[3],
72        ])
73    }
74}
75
76impl<T> Mul<Vec2<T>> for Rotation<T> where T: Zero + Unity + Neg<Output = T> + Add<Output = T> + Mul<Output = T> + Copy {
77    type Output = Vec2<T>;
78
79    fn mul(self, rhs: Vec2<T>) -> Vec2<T> {
80        // Standard matrix-vector multiplication
81        Vec2::new(
82            self.matrix[0] * rhs.x + self.matrix[1] * rhs.y,
83            self.matrix[2] * rhs.x + self.matrix[3] * rhs.y ,
84        )
85    }
86}
87
88#[cfg(test)]
89mod tests {
90    use crate::Vec2;
91
92    use super::Rotation;
93
94    #[test]
95    fn rotation() {
96        assert_eq!(Rotation::IDENTITY * Vec2::new(4, -3), Vec2::new(4, -3));
97        assert_eq!(Rotation::CW_90 * Vec2::new(2, 3), Vec2::new(-3, 2));
98        assert_eq!(Rotation::CW_90 * Vec2::<i32>::RIGHT, Vec2::DOWN);
99        assert_eq!(Rotation::CW_90 * Vec2::<i32>::DOWN, Vec2::LEFT);
100        assert_eq!(Rotation::CW_90 * Vec2::<i32>::LEFT, Vec2::UP);
101        assert_eq!(Rotation::CW_90 * Vec2::<i32>::UP, Vec2::RIGHT);
102    }
103
104    #[test]
105    fn matmul() {
106        assert_eq!(Rotation::IDENTITY * Rotation::<i32>::IDENTITY, Rotation::IDENTITY);
107        assert_eq!(Rotation::IDENTITY * Rotation::<i32>::CW_90, Rotation::CW_90);
108        assert_eq!(Rotation::CW_90 * Rotation::<i32>::CW_90, Rotation::CW_180);
109        assert_eq!(Rotation::CW_90 * Rotation::<i32>::CW_180, Rotation::CW_270);
110        assert_eq!(Rotation::CW_180 * Rotation::<i32>::CW_180, Rotation::IDENTITY);
111    }
112}
lighthouse_protocol/utils/rotation.rs

lighthouse_protocol/utils/
rotation.rs
