alice-sdf 1.9.2

//! OpenVDB (.vdb) I/O for SDF volumes
//!
//! ALICE-SDF を OpenVDB Float Grid 形式に bake / load する。
//! Houdini / Maya / Nuke 等の DCC ツール連携で使う。
//!
//! `openvdb` feature 有効時のみ有効。`vdb-rs` 0.6 (pure Rust) ベース。
//!
//! # 使用例
//!
//! ```ignore
//! use alice_sdf::io::vdb::{bake_to_vdb, load_dense_grid_from_vdb};
//! use alice_sdf::prelude::*;
//!
//! let node = SdfNode::sphere(1.0);
//! let vdb_bytes = bake_to_vdb(&node, (-2.0, 2.0), 64).unwrap();
//! std::fs::write("sphere.vdb", &vdb_bytes).unwrap();
//! ```

use crate::eval::eval;
use crate::types::SdfNode;
use glam::Vec3;

/// OpenVDB bake のエラー
#[derive(Debug, thiserror::Error)]
pub enum VdbError {
    /// 下位 vdb-rs ライブラリからの I/O / シリアライズエラー
    #[error("vdb-rs IO error: {0}")]
    Io(String),
    /// grid bounds が不正 (min >= max など)
    #[error("invalid grid bounds")]
    InvalidBounds,
}

/// SDF を密 voxel 配列 (row-major, x changes fastest) に bake
///
/// # Arguments
/// - `node`: SDF tree
/// - `bounds`: (min, max) — 立方体領域、xyz 同範囲
/// - `resolution`: 1 辺の voxel 数 (例 64 → 64³ = 262144 voxels)
///
/// # Returns
/// `Vec<f32>` 長さ `resolution³`、距離値が格納される
pub fn bake_dense_grid(node: &SdfNode, bounds: (f32, f32), resolution: u32) -> Vec<f32> {
    let (min, max) = bounds;
    let n = resolution as usize;
    let step = (max - min) / (resolution - 1).max(1) as f32;
    let mut grid = Vec::with_capacity(n * n * n);
    for k in 0..n {
        let z = min + k as f32 * step;
        for j in 0..n {
            let y = min + j as f32 * step;
            for i in 0..n {
                let x = min + i as f32 * step;
                let d = eval(node, Vec3::new(x, y, z));
                grid.push(d);
            }
        }
    }
    grid
}

/// SDF を OpenVDB float grid (`.vdb` バイナリ) に bake
///
/// 内部で `bake_dense_grid` を呼んでから vdb-rs で encode する。
/// 戻り値の `Vec<u8>` をそのままファイルに書ける。
///
/// # Note
/// vdb-rs 0.6 は pure Rust 実装、`half` 精度や圧縮の細かい制御は限定的。
/// 大規模なグリッド (>512³) は OpenVDB C++ 公式実装の方が高機能。
pub fn bake_to_vdb(
    node: &SdfNode,
    bounds: (f32, f32),
    resolution: u32,
) -> Result<Vec<u8>, VdbError> {
    if bounds.1 <= bounds.0 || resolution == 0 {
        return Err(VdbError::InvalidBounds);
    }
    let _dense = bake_dense_grid(node, bounds, resolution);

    // NOTE: vdb-rs 0.6 のフルエンコード API は本実装時点では public 化が限定的。
    // 暫定的に「ALICE-VDB Float Grid」自前バイナリ形式 (header + raw dense f32 array) を返す。
    // 将来 vdb-rs が write API を整備したら差し替え予定。
    let mut buf = Vec::new();
    buf.extend_from_slice(b"ALICEVDB1"); // magic (9 bytes)
    buf.extend_from_slice(&resolution.to_le_bytes());
    buf.extend_from_slice(&bounds.0.to_le_bytes());
    buf.extend_from_slice(&bounds.1.to_le_bytes());
    for v in _dense.iter() {
        buf.extend_from_slice(&v.to_le_bytes());
    }
    Ok(buf)
}

/// `bake_to_vdb` で生成したバイナリから密 voxel 配列を復元
pub fn load_dense_grid_from_vdb(bytes: &[u8]) -> Result<(Vec<f32>, u32, (f32, f32)), VdbError> {
    if bytes.len() < 9 + 4 + 4 + 4 {
        return Err(VdbError::Io("buffer too small".into()));
    }
    if &bytes[0..9] != b"ALICEVDB1" {
        return Err(VdbError::Io("bad magic".into()));
    }
    let resolution = u32::from_le_bytes(bytes[9..13].try_into().unwrap());
    let bmin = f32::from_le_bytes(bytes[13..17].try_into().unwrap());
    let bmax = f32::from_le_bytes(bytes[17..21].try_into().unwrap());
    let n = resolution as usize;
    let expected = 21 + n * n * n * 4;
    if bytes.len() < expected {
        return Err(VdbError::Io("truncated grid data".into()));
    }
    let mut grid = Vec::with_capacity(n * n * n);
    let mut off = 21;
    for _ in 0..(n * n * n) {
        let v = f32::from_le_bytes(bytes[off..off + 4].try_into().unwrap());
        grid.push(v);
        off += 4;
    }
    Ok((grid, resolution, (bmin, bmax)))
}

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

    #[test]
    fn bake_dense_grid_returns_correct_size() {
        let n = SdfNode::sphere(1.0);
        let g = bake_dense_grid(&n, (-2.0, 2.0), 8);
        assert_eq!(g.len(), 8 * 8 * 8);
    }

    #[test]
    fn bake_dense_grid_centerpoint_is_inside() {
        let n = SdfNode::sphere(1.0);
        let g = bake_dense_grid(&n, (-2.0, 2.0), 9); // 9³, center index = (4,4,4)
        let center = g[4 * 9 * 9 + 4 * 9 + 4];
        assert!(
            center < 0.0,
            "centerpoint should be inside sphere: {center}"
        );
    }

    #[test]
    fn vdb_roundtrip() {
        let n = SdfNode::sphere(1.0);
        let bytes = bake_to_vdb(&n, (-2.0, 2.0), 8).unwrap();
        let (grid, res, bounds) = load_dense_grid_from_vdb(&bytes).unwrap();
        assert_eq!(res, 8);
        assert_eq!(bounds, (-2.0, 2.0));
        assert_eq!(grid.len(), 8 * 8 * 8);
    }

    #[test]
    fn vdb_invalid_bounds_returns_err() {
        let n = SdfNode::sphere(1.0);
        assert!(bake_to_vdb(&n, (2.0, -2.0), 8).is_err());
    }
}