alice-sdf 5.1.0

//! Chamfer CSG operations for SDFs (Deep Fried Edition)
//!
//! 45-degree beveled blends. Union: `min(a, b, (a + b)·√½ − r)`, intersection
//! and subtraction are the duals (`max(a, b, (a + b)·√½ + r)` etc.).
//!
//! # Canonical form (decided 2026-09-14)
//!
//! This is **not** the hg_sdf `fOpUnionChamfer` formula, which is
//! `min(a, b, (a − r + b)·√½)`; the two differ by `r·(1 − √½) ≈ 0.29·r`
//! (ALICE-SDF cuts the full `r`, hg_sdf only `r·√½`). Both are valid chamfers.
//! ALICE-SDF keeps its form because every evaluation path (tree / bytecode /
//! SIMD / JIT / GLSL / WGSL / HLSL) and the published crates.io API already
//! agree on it; ALICE-SDF-Effect's `hg_sdf` module deliberately keeps the
//! hg_sdf form for shader-library parity. Do not "fix" one to match the other.
//!
//! # Deep Fried Optimizations
//! - **Branchless**: No conditionals in hot path.
//! - **Division Exorcism**: `_rr` variants use precomputed `1/r` where needed.
//! - **Forced Inlining**: `#[inline(always)]` guarantees no call overhead.
//!
//! Author: Moroya Sakamoto

use crate::compiled::real::Real;
use std::f32::consts::FRAC_1_SQRT_2;

/// Chamfer minimum: 45-degree beveled blend (Deep Fried)
///
/// Creates a flat 45-degree chamfer at the junction of two SDFs.
/// Formula: `min(min(a, b), (a + b) * FRAC_1_SQRT_2 - r)` (see the module
/// docs for how this relates to hg_sdf's `fOpUnionChamfer`).
#[inline(always)]
pub fn chamfer_min(a: f32, b: f32, r: f32) -> f32 {
    chamfer_min_r::<f32>(a, b, r)
}

/// Chamfer maximum: 45-degree beveled blend (Deep Fried)
///
/// Dual of chamfer_min for intersection operations.
#[inline(always)]
pub fn chamfer_max(a: f32, b: f32, r: f32) -> f32 {
    -chamfer_min(-a, -b, r)
}

/// Chamfer union of two SDFs
#[inline(always)]
pub fn sdf_chamfer_union(d1: f32, d2: f32, r: f32) -> f32 {
    chamfer_min(d1, d2, r)
}

/// Chamfer intersection of two SDFs
#[inline(always)]
pub fn sdf_chamfer_intersection(d1: f32, d2: f32, r: f32) -> f32 {
    chamfer_max(d1, d2, r)
}

/// Chamfer subtraction of B from A
#[inline(always)]
pub fn sdf_chamfer_subtraction(d1: f32, d2: f32, r: f32) -> f32 {
    chamfer_max(d1, -d2, r)
}

/// Chamfer minimum (generic over [`Real`]).
#[inline(always)]
pub fn chamfer_min_r<R: Real>(a: R, b: R, r: f32) -> R {
    a.min(b)
        .min((a + b) * R::splat(FRAC_1_SQRT_2) - R::splat(r))
}

/// Chamfer maximum (generic over [`Real`]).
#[inline(always)]
pub fn chamfer_max_r<R: Real>(a: R, b: R, r: f32) -> R {
    -chamfer_min_r(-a, -b, r)
}

/// Chamfer union (generic).
#[inline(always)]
pub fn sdf_chamfer_union_r<R: Real>(d1: R, d2: R, r: f32) -> R {
    chamfer_min_r(d1, d2, r)
}

/// Chamfer intersection (generic).
#[inline(always)]
pub fn sdf_chamfer_intersection_r<R: Real>(d1: R, d2: R, r: f32) -> R {
    chamfer_max_r(d1, d2, r)
}

/// Chamfer subtraction (generic).
#[inline(always)]
pub fn sdf_chamfer_subtraction_r<R: Real>(d1: R, d2: R, r: f32) -> R {
    chamfer_max_r(d1, -d2, r)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_chamfer_union_basic() {
        // When both shapes are far apart, should behave like min
        let a = 5.0;
        let b = 10.0;
        let r = 0.5;
        let result = sdf_chamfer_union(a, b, r);
        assert!(result <= a, "chamfer union should be <= min(a,b)");
    }

    #[test]
    fn test_chamfer_union_symmetry() {
        let d1 = 0.5;
        let d2 = 0.8;
        let r = 0.3;
        assert!((sdf_chamfer_union(d1, d2, r) - sdf_chamfer_union(d2, d1, r)).abs() < 1e-6);
    }

    #[test]
    fn test_chamfer_intersection() {
        // Chamfer intersection should be >= max(a,b) when shapes barely overlap
        let d1 = -0.5;
        let d2 = -0.3;
        let r = 0.1;
        let result = sdf_chamfer_intersection(d1, d2, r);
        assert!(result >= d1.max(d2) - r * 2.0);
    }

    #[test]
    fn test_chamfer_creates_bevel() {
        // Near the junction (a≈b≈0), chamfer term should dominate
        let a = 0.1;
        let b = 0.1;
        let r = 0.5;
        let chamfer = sdf_chamfer_union(a, b, r);
        let hard_union = a.min(b);
        // Chamfer should cut more than hard union at the junction
        assert!(chamfer < hard_union);
    }
}