oxiphysics-softbody 0.1.1

Soft body simulation for the OxiPhysics engine
Documentation 
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// Copyright 2026 COOLJAPAN OU (Team KitaSan)
// SPDX-License-Identifier: Apache-2.0

//! Internal 3x3 matrix helper functions for FEM computations.

#[allow(dead_code)]
pub(super) fn edge_matrix_raw(
    p0: [f64; 3],
    p1: [f64; 3],
    p2: [f64; 3],
    p3: [f64; 3],
) -> [[f64; 3]; 3] {
    [
        [p1[0] - p0[0], p2[0] - p0[0], p3[0] - p0[0]],
        [p1[1] - p0[1], p2[1] - p0[1], p3[1] - p0[1]],
        [p1[2] - p0[2], p2[2] - p0[2], p3[2] - p0[2]],
    ]
}

#[allow(dead_code)]
pub(super) fn det3x3(m: [[f64; 3]; 3]) -> f64 {
    m[0][0] * (m[1][1] * m[2][2] - m[1][2] * m[2][1])
        - m[0][1] * (m[1][0] * m[2][2] - m[1][2] * m[2][0])
        + m[0][2] * (m[1][0] * m[2][1] - m[1][1] * m[2][0])
}

#[allow(dead_code)]
pub(super) fn inv3x3(m: [[f64; 3]; 3]) -> [[f64; 3]; 3] {
    let det = det3x3(m);
    if det.abs() < 1e-30 {
        return [[1.0, 0.0, 0.0], [0.0, 1.0, 0.0], [0.0, 0.0, 1.0]];
    }
    let inv_det = 1.0 / det;
    [
        [
            (m[1][1] * m[2][2] - m[1][2] * m[2][1]) * inv_det,
            (m[0][2] * m[2][1] - m[0][1] * m[2][2]) * inv_det,
            (m[0][1] * m[1][2] - m[0][2] * m[1][1]) * inv_det,
        ],
        [
            (m[1][2] * m[2][0] - m[1][0] * m[2][2]) * inv_det,
            (m[0][0] * m[2][2] - m[0][2] * m[2][0]) * inv_det,
            (m[0][2] * m[1][0] - m[0][0] * m[1][2]) * inv_det,
        ],
        [
            (m[1][0] * m[2][1] - m[1][1] * m[2][0]) * inv_det,
            (m[0][1] * m[2][0] - m[0][0] * m[2][1]) * inv_det,
            (m[0][0] * m[1][1] - m[0][1] * m[1][0]) * inv_det,
        ],
    ]
}

#[allow(dead_code)]
pub(super) fn inv3x3_transpose(m: [[f64; 3]; 3]) -> [[f64; 3]; 3] {
    transpose3x3(inv3x3(m))
}

#[allow(dead_code)]
pub(super) fn transpose3x3(m: [[f64; 3]; 3]) -> [[f64; 3]; 3] {
    [
        [m[0][0], m[1][0], m[2][0]],
        [m[0][1], m[1][1], m[2][1]],
        [m[0][2], m[1][2], m[2][2]],
    ]
}

#[allow(dead_code)]
pub(super) fn mul3x3(a: [[f64; 3]; 3], b: [[f64; 3]; 3]) -> [[f64; 3]; 3] {
    let mut c = [[0.0_f64; 3]; 3];
    for i in 0..3 {
        for j in 0..3 {
            for k in 0..3 {
                c[i][j] += a[i][k] * b[k][j];
            }
        }
    }
    c
}

/// Build the 6x6 isotropic linear-elastic constitutive matrix D in Voigt
/// notation.
#[allow(dead_code)]
pub(super) fn isotropic_d_matrix(lambda: f64, mu: f64) -> [[f64; 6]; 6] {
    let l2m = lambda + 2.0 * mu;
    [
        [l2m, lambda, lambda, 0.0, 0.0, 0.0],
        [lambda, l2m, lambda, 0.0, 0.0, 0.0],
        [lambda, lambda, l2m, 0.0, 0.0, 0.0],
        [0.0, 0.0, 0.0, mu, 0.0, 0.0],
        [0.0, 0.0, 0.0, 0.0, mu, 0.0],
        [0.0, 0.0, 0.0, 0.0, 0.0, mu],
    ]
}