alice-sdf 1.13.0

//! Twist modifier for SDFs (Deep Fried Edition)
//!
//! # Deep Fried Optimizations
//! - **Simultaneous Trig**: Uses `sin_cos()` for single-instruction computation.
//! - **Forced Inlining**: `#[inline(always)]`.
//!
//! Author: Moroya Sakamoto

use glam::Vec3;

/// Twist space around the Y-axis
#[inline(always)]
pub fn modifier_twist(point: Vec3, strength: f32) -> Vec3 {
    let (s, c) = (point.y * strength).sin_cos();
    Vec3::new(
        point.x.mul_add(c, -(point.z * s)),
        point.y,
        point.x.mul_add(s, point.z * c),
    )
}

/// Twist space around the X-axis
#[inline(always)]
pub fn modifier_twist_x(point: Vec3, strength: f32) -> Vec3 {
    let (s, c) = (point.x * strength).sin_cos();
    Vec3::new(
        point.x,
        point.y.mul_add(c, -(point.z * s)),
        point.y.mul_add(s, point.z * c),
    )
}

/// Twist space around the Z-axis
#[inline(always)]
pub fn modifier_twist_z(point: Vec3, strength: f32) -> Vec3 {
    let (s, c) = (point.z * strength).sin_cos();
    Vec3::new(
        point.x.mul_add(c, -(point.y * s)),
        point.x.mul_add(s, point.y * c),
        point.z,
    )
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::f32::consts::PI;

    #[test]
    fn test_twist_equivalence() {
        let p = Vec3::new(1.0, 2.0, 3.0);
        let s = 0.5;
        let t1 = modifier_twist(p, s);
        // Manual calc
        let a = p.y * s;
        let t2 = Vec3::new(
            p.x.mul_add(a.cos(), -(p.z * a.sin())),
            p.y,
            p.x.mul_add(a.sin(), p.z * a.cos()),
        );
        assert!((t1 - t2).length() < 1e-6);
    }

    #[test]
    fn test_twist_at_origin() {
        let point = Vec3::new(1.0, 0.0, 0.0);
        let result = modifier_twist(point, 1.0);
        assert!((result - point).length() < 0.0001);
    }

    #[test]
    fn test_twist_90_degrees() {
        let point = Vec3::new(1.0, PI / 2.0, 0.0);
        let result = modifier_twist(point, 1.0);
        let expected = Vec3::new(0.0, PI / 2.0, 1.0);
        assert!((result - expected).length() < 0.0001);
    }
}