alice-sdf 5.0.0

//! Variable-thickness offset surface (shell) modifier
//!
//! Creates a hollow shell around an SDF surface with independently
//! configurable inner and outer offsets. Unlike the `Onion` modifier
//! which applies uniform thickness, `ShellConfig` allows asymmetric
//! inner/outer expansion.
//!
//! # Example
//!
//! ```rust
//! use alice_sdf::shell::{ShellConfig, eval_shell};
//! use alice_sdf::types::SdfNode;
//! use glam::Vec3;
//!
//! let sphere = SdfNode::sphere(1.0);
//! let config = ShellConfig::new(0.1, 0.2); // inner=0.1, outer=0.2
//! let d = eval_shell(&sphere, Vec3::new(1.15, 0.0, 0.0), &config);
//! // Point is inside the shell wall
//! ```
//!
//! Author: Moroya Sakamoto

use crate::compiled::{eval_compiled, CompiledSdf};
use crate::eval::{eval, eval_gradient};
use crate::types::SdfNode;
use glam::Vec3;
use rayon::prelude::*;
use std::sync::Arc;

/// Configuration for the shell modifier.
///
/// `inner_offset` controls how far inward the shell extends from the original surface.
/// `outer_offset` controls how far outward the shell extends.
///
/// The resulting shell occupies the region: `-inner_offset <= sdf(p) <= outer_offset`.
#[derive(Debug, Clone, Copy)]
pub struct ShellConfig {
    /// Inward shell thickness (positive = shrinks inward from surface).
    pub inner_offset: f32,
    /// Outward shell thickness (positive = expands outward from surface).
    pub outer_offset: f32,
}

impl ShellConfig {
    /// Create a new shell configuration.
    #[inline]
    pub const fn new(inner_offset: f32, outer_offset: f32) -> Self {
        Self {
            inner_offset,
            outer_offset,
        }
    }

    /// Uniform thickness shell (same inner and outer offset).
    #[inline]
    pub const fn uniform(thickness: f32) -> Self {
        Self {
            inner_offset: thickness,
            outer_offset: thickness,
        }
    }

    /// Total wall thickness.
    #[inline]
    pub fn wall_thickness(self) -> f32 {
        self.inner_offset + self.outer_offset
    }
}

impl Default for ShellConfig {
    fn default() -> Self {
        Self {
            inner_offset: 0.1,
            outer_offset: 0.1,
        }
    }
}

/// Evaluate the shell SDF at a point.
///
/// The shell SDF is defined as: `max(sdf(p) - outer, -(sdf(p) + inner))`
///
/// - Positive: outside the shell
/// - Negative: inside the shell wall
/// - Zero: on either the inner or outer surface
#[inline]
pub fn eval_shell(node: &SdfNode, point: Vec3, config: &ShellConfig) -> f32 {
    let d = eval(node, point);
    let outer_surface = d - config.outer_offset;
    let inner_surface = -(d + config.inner_offset);
    outer_surface.max(inner_surface)
}

/// Evaluate shell SDF for a batch of points.
pub fn eval_shell_batch(node: &SdfNode, points: &[Vec3], config: &ShellConfig) -> Vec<f32> {
    points
        .iter()
        .map(|&p| eval_shell(node, p, config))
        .collect()
}

/// Evaluate shell SDF for a batch of points in parallel (Rayon).
pub fn eval_shell_batch_parallel(
    node: &SdfNode,
    points: &[Vec3],
    config: &ShellConfig,
) -> Vec<f32> {
    points
        .par_iter()
        .map(|&p| eval_shell(node, p, config))
        .collect()
}

/// Evaluate the shell gradient (outward-pointing normal) at a point.
///
/// Returns the normalized gradient of the shell SDF.
pub fn eval_shell_gradient(node: &SdfNode, point: Vec3, config: &ShellConfig) -> Vec3 {
    let d = eval(node, point);
    let g = eval_gradient(node, point);
    let outer_surface = d - config.outer_offset;
    let inner_surface = -(d + config.inner_offset);
    if outer_surface >= inner_surface {
        // On/near outer surface: gradient = gradient of sdf
        g
    } else {
        // On/near inner surface: gradient = -gradient of sdf
        -g
    }
}

/// Evaluate shell SDF using a pre-compiled SDF for better performance.
#[inline]
pub fn eval_shell_compiled(compiled: &CompiledSdf, point: Vec3, config: &ShellConfig) -> f32 {
    let d = eval_compiled(compiled, point);
    let outer_surface = d - config.outer_offset;
    let inner_surface = -(d + config.inner_offset);
    outer_surface.max(inner_surface)
}

/// Batch evaluate shell SDF using a compiled SDF in parallel.
pub fn eval_shell_compiled_batch_parallel(
    compiled: &CompiledSdf,
    points: &[Vec3],
    config: &ShellConfig,
) -> Vec<f32> {
    points
        .par_iter()
        .map(|&p| eval_shell_compiled(compiled, p, config))
        .collect()
}

/// Create an SdfNode that wraps a child in a shell.
///
/// The node evaluates to the same field as [`eval_shell`]:
/// `max(d - outer, -(d + inner)) = |d - c| - h` with `c = (outer - inner) / 2`
/// (the centre of the band) and `h = (outer + inner) / 2` (its half width),
/// built as `Onion { Round { child, radius: c }, thickness: h }`.
/// For simple shells, prefer `eval_shell()` directly for better performance.
pub fn shell_node(child: Arc<SdfNode>, config: ShellConfig) -> SdfNode {
    let half_thick = f32::midpoint(config.inner_offset, config.outer_offset);
    let center_offset = (config.outer_offset - config.inner_offset) * 0.5;

    if center_offset.abs() < 1e-6 {
        // Symmetric: the band is centred on the surface, Onion alone
        SdfNode::Onion {
            child,
            thickness: half_thick,
        }
    } else {
        // Asymmetric: move the band centre to d = c first (Round gives d - c),
        // then take the band of half width h around it (Onion gives |·| - h)
        SdfNode::Onion {
            child: Arc::new(SdfNode::Round {
                child,
                radius: center_offset,
            }),
            thickness: half_thick,
        }
    }
}

// ── Tests ────────────────────────────────────────────────────

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

    #[test]
    fn shell_outside() {
        let sphere = SdfNode::sphere(1.0);
        let config = ShellConfig::new(0.1, 0.1);
        // Point well outside outer surface
        let d = eval_shell(&sphere, Vec3::new(2.0, 0.0, 0.0), &config);
        assert!(d > 0.0);
    }

    #[test]
    fn shell_inside_wall() {
        let sphere = SdfNode::sphere(1.0);
        let config = ShellConfig::new(0.1, 0.1);
        // Point on the original surface: sdf=0, shell = max(-0.1, -0.1) = -0.1
        let d = eval_shell(&sphere, Vec3::new(1.0, 0.0, 0.0), &config);
        assert!(d < 0.0);
    }

    #[test]
    fn shell_hollow_center() {
        let sphere = SdfNode::sphere(1.0);
        let config = ShellConfig::new(0.1, 0.1);
        // Origin: sdf = -1.0, shell = max(-1.1, -(-1.0 + 0.1)) = max(-1.1, 0.9) = 0.9
        let d = eval_shell(&sphere, Vec3::ZERO, &config);
        assert!(d > 0.0, "Center should be outside shell (hollow)");
    }

    #[test]
    fn shell_outer_boundary() {
        let sphere = SdfNode::sphere(1.0);
        let config = ShellConfig::new(0.1, 0.2);
        // At distance 1.2 from center: sdf=0.2, shell = max(0.0, -0.3) = 0.0
        let d = eval_shell(&sphere, Vec3::new(1.2, 0.0, 0.0), &config);
        assert!(d.abs() < 1e-4, "Should be on outer surface, got {}", d);
    }

    #[test]
    fn shell_inner_boundary() {
        let sphere = SdfNode::sphere(1.0);
        let config = ShellConfig::new(0.1, 0.2);
        // At distance 0.9 from center: sdf=-0.1, shell = max(-0.3, 0.0) = 0.0
        let d = eval_shell(&sphere, Vec3::new(0.9, 0.0, 0.0), &config);
        assert!(d.abs() < 1e-4, "Should be on inner surface, got {}", d);
    }

    #[test]
    fn shell_asymmetric() {
        let sphere = SdfNode::sphere(1.0);
        let config = ShellConfig::new(0.05, 0.3);
        // Total wall = 0.35
        assert!((config.wall_thickness() - 0.35).abs() < 1e-6);

        // Inside wall at original surface
        let d = eval_shell(&sphere, Vec3::new(1.0, 0.0, 0.0), &config);
        assert!(d < 0.0);
    }

    #[test]
    fn shell_zero_thickness() {
        let sphere = SdfNode::sphere(1.0);
        let config = ShellConfig::new(0.0, 0.0);
        // Zero-thickness shell: same as original surface
        let d = eval_shell(&sphere, Vec3::new(1.0, 0.0, 0.0), &config);
        assert!(d.abs() < 1e-5);
    }

    #[test]
    fn shell_batch() {
        let sphere = SdfNode::sphere(1.0);
        let config = ShellConfig::new(0.1, 0.1);
        let points = vec![
            Vec3::new(2.0, 0.0, 0.0),
            Vec3::new(1.0, 0.0, 0.0),
            Vec3::ZERO,
        ];
        let results = eval_shell_batch(&sphere, &points, &config);
        assert_eq!(results.len(), 3);
        assert!(results[0] > 0.0); // outside
        assert!(results[1] < 0.0); // in wall
        assert!(results[2] > 0.0); // hollow center
    }

    #[test]
    fn shell_uniform_config() {
        let config = ShellConfig::uniform(0.5);
        assert_eq!(config.inner_offset, 0.5);
        assert_eq!(config.outer_offset, 0.5);
        assert!((config.wall_thickness() - 1.0).abs() < 1e-6);
    }

    #[test]
    fn shell_node_symmetric() {
        let child = Arc::new(SdfNode::sphere(1.0));
        let config = ShellConfig::uniform(0.1);
        let node = shell_node(child, config);
        // Should produce an Onion node for symmetric case
        match node {
            SdfNode::Onion { thickness, .. } => {
                assert!((thickness - 0.1).abs() < 1e-6);
            }
            _ => panic!("Expected Onion node for symmetric shell"),
        }
    }

    #[test]
    fn shell_default_config() {
        let config = ShellConfig::default();
        assert_eq!(config.inner_offset, 0.1);
        assert_eq!(config.outer_offset, 0.1);
    }

    #[test]
    fn shell_batch_parallel_matches_sequential() {
        let sphere = SdfNode::sphere(1.0);
        let config = ShellConfig::new(0.1, 0.1);
        let points: Vec<Vec3> = (0..100)
            .map(|i| {
                let t = i as f32 / 50.0;
                Vec3::new(t, 0.0, 0.0)
            })
            .collect();
        let seq = eval_shell_batch(&sphere, &points, &config);
        let par = super::eval_shell_batch_parallel(&sphere, &points, &config);
        for (s, p) in seq.iter().zip(par.iter()) {
            assert!((s - p).abs() < 1e-6);
        }
    }

    #[test]
    fn shell_gradient_outer() {
        let sphere = SdfNode::sphere(1.0);
        let config = ShellConfig::new(0.1, 0.1);
        // Point on outer surface: gradient should point outward (+x)
        let g = super::eval_shell_gradient(&sphere, Vec3::new(1.05, 0.0, 0.0), &config);
        assert!(g.x > 0.5, "gradient x={}", g.x);
    }

    #[test]
    fn shell_gradient_inner() {
        let sphere = SdfNode::sphere(1.0);
        let config = ShellConfig::new(0.1, 0.1);
        // Point on inner surface: gradient should point inward (-x from sphere center)
        let g = super::eval_shell_gradient(&sphere, Vec3::new(0.95, 0.0, 0.0), &config);
        // Inner surface gradient = -sdf_gradient → points inward
        assert!(g.x < -0.5, "gradient x={}", g.x);
    }

    #[test]
    fn shell_compiled_matches_interpreted() {
        use crate::compiled::CompiledSdf;
        let sphere = SdfNode::sphere(1.0);
        let compiled = CompiledSdf::compile(&sphere);
        let config = ShellConfig::new(0.1, 0.2);
        let points = [
            Vec3::new(2.0, 0.0, 0.0),
            Vec3::new(1.0, 0.0, 0.0),
            Vec3::ZERO,
            Vec3::new(0.9, 0.0, 0.0),
            Vec3::new(1.2, 0.0, 0.0),
        ];
        for p in points {
            let interp = eval_shell(&sphere, p, &config);
            let comp = super::eval_shell_compiled(&compiled, p, &config);
            assert!(
                (interp - comp).abs() < 1e-4,
                "mismatch at {:?}: {} vs {}",
                p,
                interp,
                comp
            );
        }
    }

    #[test]
    fn shell_compiled_batch_parallel() {
        use crate::compiled::CompiledSdf;
        let sphere = SdfNode::sphere(1.0);
        let compiled = CompiledSdf::compile(&sphere);
        let config = ShellConfig::new(0.1, 0.1);
        let points: Vec<Vec3> = (0..50)
            .map(|i| Vec3::new(i as f32 * 0.1, 0.0, 0.0))
            .collect();
        let results = super::eval_shell_compiled_batch_parallel(&compiled, &points, &config);
        assert_eq!(results.len(), 50);
        // Spot-check a few
        for (i, &p) in points.iter().enumerate() {
            let expected = super::eval_shell_compiled(&compiled, p, &config);
            assert!((results[i] - expected).abs() < 1e-6);
        }
    }

    #[test]
    fn shell_node_asymmetric() {
        let child = Arc::new(SdfNode::sphere(1.0));
        let config = ShellConfig::new(0.05, 0.3);
        let node = shell_node(child, config);
        // Asymmetric: Onion over a Round that moves the band centre
        match &node {
            SdfNode::Onion { child, thickness } => {
                assert!((thickness - 0.175).abs() < 1e-6);
                assert!(
                    matches!(**child, SdfNode::Round { radius, .. } if (radius - 0.125).abs() < 1e-6)
                );
            }
            _ => panic!("Expected Onion(Round) node for asymmetric shell"),
        }
    }
}