lunar-bsp-build 1.0.0

//! offline BSP tree and PVS compiler for Lunar levels.
//!
//! call from your crate's `build.rs` to compile a level mesh into a binary blob
//! that [`BspLevel`][lunar_bsp::level::BspLevel] can load at runtime with zero
//! parsing cost.
//!
//! # build.rs example
//!
//! ```ignore
//! fn main() {
//!     let blob = lunar_bsp_build::compile_bsp_file("assets/levels/level1.glb").unwrap();
//!     let out = std::path::PathBuf::from(std::env::var("OUT_DIR").unwrap());
//!     std::fs::write(out.join("level1.bsp"), blob).unwrap();
//!     println!("cargo:rerun-if-changed=assets/levels/level1.glb");
//! }
//! ```
//!
//! then in your game:
//!
//! ```ignore
//! let level = BspLevel::from_binary(include_bytes!(concat!(env!("OUT_DIR"), "/level1.bsp")))
//!     .expect("level bsp corrupt");
//! app.insert_resource(level);
//! ```
//!
//! # area ids
//!
//! name your GLTF meshes with an `areaN_` prefix (e.g. `area0_floor`, `area1_corridor`)
//! to automatically assign area ids. meshes without this prefix are untagged and
//! treated as always-visible geometry.
//!
//! portal hints let you override the auto-detected portals or add portals where
//! the geometry auto-detection misses connections.

pub mod gltf;
pub mod partition;
pub mod portal;
pub mod pvs;

pub use portal::BspPortalHint;

use lunar_bsp::level::BspBlob;
use lunar_math::Vec3;
use partition::{InputTriangle, build_bsp};
use portal::extract_portals;
use pvs::compute_pvs;

/// a mesh to include in the BSP compilation.
///
/// all vertices must be in world space (apply node transforms before passing in).
/// if loading from GLTF, use [`compile_bsp_file`] which handles transforms automatically.
pub struct BspInputMesh {
	/// world-space vertex positions.
	pub vertices: Vec<Vec3>,
	/// triangle index list (every 3 indices = one triangle).
	pub indices: Vec<u32>,
	/// area id for portal culling. `None` = always-visible (not portal-culled).
	pub area_id: Option<u32>,
}

/// configuration for the BSP compiler.
pub struct BspCompileConfig {
	/// maximum number of triangles per BSP leaf before forcing a split. default: 16.
	pub max_leaf_size: usize,
	/// number of random ray pairs to cast per leaf pair for PVS computation. default: 64.
	pub pvs_samples: usize,
	/// if > 0, leaf pairs whose centroids are farther apart than this distance (in
	/// world units) are assumed not visible and skipped. default: 0 (always test).
	pub pvs_skip_distance: f32,
}

impl Default for BspCompileConfig {
	fn default() -> Self {
		Self {
			max_leaf_size: 16,
			pvs_samples: 64,
			pvs_skip_distance: 0.0,
		}
	}
}

/// compile a set of meshes into a BSP blob.
///
/// `hints` provides optional designer-placed portals. if empty, portals are
/// auto-detected from adjacent leaf AABBs.
///
/// # Errors
///
/// returns an error string if no triangles are found or serialization fails.
pub fn compile_bsp(
	meshes: &[BspInputMesh],
	hints: &[BspPortalHint],
	config: &BspCompileConfig,
) -> Result<Vec<u8>, String> {
	// flatten all meshes into a single triangle list
	let mut triangles: Vec<InputTriangle> = Vec::new();
	let mut all_tris: Vec<[Vec3; 3]> = Vec::new();

	for mesh in meshes {
		let verts = &mesh.vertices;
		let mut i = 0;
		while i + 2 < mesh.indices.len() {
			let i0 = mesh.indices[i] as usize;
			let i1 = mesh.indices[i + 1] as usize;
			let i2 = mesh.indices[i + 2] as usize;
			if i0 >= verts.len() || i1 >= verts.len() || i2 >= verts.len() {
				i += 3;
				continue;
			}
			let orig_idx = triangles.len() as u32;
			triangles.push(InputTriangle {
				verts: [verts[i0], verts[i1], verts[i2]],
				area_id: mesh.area_id,
				original_index: orig_idx,
			});
			all_tris.push([verts[i0], verts[i1], verts[i2]]);
			i += 3;
		}
	}

	if triangles.is_empty() {
		return Err("compile_bsp: no valid triangles in input meshes".into());
	}

	// build BSP tree
	let partition = build_bsp(&triangles, config.max_leaf_size);

	// compute PVS
	let skip_dist_sq = if config.pvs_skip_distance > 0.0 {
		config.pvs_skip_distance * config.pvs_skip_distance
	} else {
		0.0
	};
	let pvs = compute_pvs(
		&partition.leaf_aabbs,
		&all_tris,
		config.pvs_samples,
		skip_dist_sq,
	);

	// extract portals
	let portals = extract_portals(&partition.leaf_aabbs, &partition.leaf_areas, hints);

	// build area map: (leaf_index, area_id) for tagged leaves, sorted for binary search at runtime
	let mut area_map: Vec<(u32, u32)> = partition
		.leaf_areas
		.iter()
		.enumerate()
		.filter_map(|(leaf, area)| area.map(|a| (leaf as u32, a)))
		.collect();
	area_map.sort_unstable_by_key(|&(li, _)| li);

	let blob = BspBlob {
		nodes: partition.nodes,
		leaf_triangles: partition.leaf_triangles,
		pvs: pvs.data,
		pvs_stride: pvs.stride,
		leaf_count: partition.leaf_count,
		portals,
		area_map,
	};

	bincode::serialize(&blob).map_err(|error| format!("bsp serialize error: {error}"))
}

/// compile a GLTF/GLB level file into a BSP blob using default settings.
///
/// equivalent to loading with [`gltf::load_gltf_meshes`] then calling [`compile_bsp`]
/// with default config and no hints.
///
/// # Errors
///
/// returns an error if the file cannot be read, parsed, or compiled.
pub fn compile_bsp_file(path: &str) -> Result<Vec<u8>, String> {
	compile_bsp_file_with_config(path, &[], &BspCompileConfig::default())
}

/// compile a GLTF/GLB level file with explicit portal hints and compile config.
///
/// # Errors
///
/// returns an error if the file cannot be read, parsed, or compiled.
pub fn compile_bsp_file_with_config(
	path: &str,
	hints: &[BspPortalHint],
	config: &BspCompileConfig,
) -> Result<Vec<u8>, String> {
	let meshes = gltf::load_gltf_meshes(path)?;
	compile_bsp(&meshes, hints, config)
}

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

	fn unit_cube_mesh(area_id: Option<u32>) -> BspInputMesh {
		// 12 triangles for a unit cube [0,1]^3
		let v = |x: f32, y: f32, z: f32| Vec3::new(x, y, z);
		let verts = vec![
			v(0.0, 0.0, 0.0),
			v(1.0, 0.0, 0.0),
			v(1.0, 1.0, 0.0),
			v(0.0, 1.0, 0.0), // front
			v(0.0, 0.0, 1.0),
			v(1.0, 0.0, 1.0),
			v(1.0, 1.0, 1.0),
			v(0.0, 1.0, 1.0), // back
		];
		let indices = vec![
			0, 1, 2, 0, 2, 3, // front
			4, 6, 5, 4, 7, 6, // back
			0, 4, 5, 0, 5, 1, // bottom
			3, 2, 6, 3, 6, 7, // top
			0, 3, 7, 0, 7, 4, // left
			1, 5, 6, 1, 6, 2, // right
		];
		BspInputMesh {
			vertices: verts,
			indices,
			area_id,
		}
	}

	#[test]
	fn compile_and_load_round_trip() {
		let mesh = unit_cube_mesh(Some(0));
		let blob = compile_bsp(&[mesh], &[], &BspCompileConfig::default()).unwrap();
		let level = BspLevel::from_binary(&blob).unwrap();
		assert!(level.is_loaded());
		let leaf = level.camera_leaf(Vec3::new(0.5, 0.5, 0.5));
		let visible = level.visible_leaves(leaf);
		assert!(
			!visible.is_empty(),
			"camera leaf should see at least itself"
		);
	}

	#[test]
	fn two_area_portals_detected() {
		// two cubes side-by-side, different areas — should auto-detect a portal
		let mesh_a = unit_cube_mesh(Some(0));
		let mesh_b = BspInputMesh {
			vertices: unit_cube_mesh(Some(1))
				.vertices
				.iter()
				.map(|v| Vec3::new(v.x + 1.0, v.y, v.z))
				.collect(),
			indices: unit_cube_mesh(Some(1)).indices,
			area_id: Some(1),
		};
		let blob = compile_bsp(
			&[mesh_a, mesh_b],
			&[],
			&BspCompileConfig {
				pvs_samples: 8,
				..Default::default()
			},
		)
		.unwrap();
		let level = BspLevel::from_binary(&blob).unwrap();
		assert!(level.is_loaded());
	}

	#[test]
	fn empty_input_is_error() {
		assert!(compile_bsp(&[], &[], &BspCompileConfig::default()).is_err());
	}

	#[test]
	fn file_not_found_is_error() {
		assert!(compile_bsp_file("does_not_exist.glb").is_err());
	}
}