voxel-rs/src/math.rs

/// Linear interpolation.
#[inline]
pub fn lerp(a: f32, b: f32, w: f32) -> f32 {
    assert!(0.0 <= w && w <= 1.0);
    a + (b - a) * w
}

/// Bilinear interpolation.
/// Expected order of `p` is from a nested `for` loop with the outer loop being `y`.
/// `w` is expected to be `[wx, wy]`
#[inline]
pub fn bi_lerp(p: &[f32], w: &[f32]) -> f32 {
    assert_eq!(p.len(), 4);
    assert_eq!(w.len(), 2);

    lerp(lerp(p[0], p[1], w[0]), lerp(p[2], p[3], w[0]), w[1])
}

/// Trilinear interpolation.
/// Expected order of `p` is from a nested `for` loop with the outer loop being `z`.
/// `w` is expected to be `[wx, wy, wz]`.
#[inline]
pub fn tri_lerp(p: &[f32], w: &[f32]) -> f32 {
    assert_eq!(p.len(), 8);
    assert_eq!(w.len(), 3);

    let c00 = p[0] + (p[1] - p[0]) * w[0];
    let c10 = p[2] + (p[3] - p[2]) * w[0];
    let c01 = p[4] + (p[5] - p[4]) * w[0];
    let c11 = p[6] + (p[7] - p[6]) * w[0];
    let c0 = c00 + (c10 - c00) * w[1];
    let c1 = c01 + (c11 - c01) * w[1];
    c0 + (c1 - c0) * w[2]
}

/// Maps a 3d index to a 1d index
pub fn to_1d_index(p: glam::UVec3, dim: glam::UVec3) -> usize {
    (p.x + p.y * dim.x + p.z * dim.x * dim.y) as usize
}