feat: add terrain-core, tma, and unitdat crates with parsing functionality

- Introduced `terrain-core` crate for loading and processing terrain mesh data.
- Added `tma` crate for parsing mission files, including footer and object records.
- Created `unitdat` crate for reading unit data files with validation of structure.
- Implemented error handling and tests for all new crates.
- Documented object registry format and rendering pipeline in specifications.

1 files changed, 281 insertions, 0 deletions

diff --git a/crates/terrain-core/src/lib.rs b/crates/terrain-core/src/lib.rs
new file mode 100644
index 0000000..36a3e42
--- /dev/null
+++ b/crates/terrain-core/src/lib.rs
@@ -0,0 +1,281 @@
+use nres::Archive;
+use std::fmt;
+use std::path::Path;
+
+pub const TERRAIN_UV_SCALE: f32 = 1024.0;
+
+pub type Result<T> = core::result::Result<T, Error>;
+
+#[derive(Debug)]
+pub enum Error {
+    Nres(nres::error::Error),
+    MissingChunk(&'static str),
+    InvalidChunkSize {
+        label: &'static str,
+        size: usize,
+        stride: usize,
+    },
+    VertexCountOverflow {
+        count: usize,
+    },
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Nres(err) => write!(f, "{err}"),
+            Self::MissingChunk(label) => write!(f, "missing required terrain chunk: {label}"),
+            Self::InvalidChunkSize {
+                label,
+                size,
+                stride,
+            } => write!(
+                f,
+                "invalid chunk size for {label}: {size} (must be divisible by {stride})"
+            ),
+            Self::VertexCountOverflow { count } => {
+                write!(f, "terrain vertex count {count} exceeds u16 range")
+            }
+        }
+    }
+}
+
+impl std::error::Error for Error {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Self::Nres(err) => Some(err),
+            _ => None,
+        }
+    }
+}
+
+impl From<nres::error::Error> for Error {
+    fn from(value: nres::error::Error) -> Self {
+        Self::Nres(value)
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct TerrainMesh {
+    pub positions: Vec<[f32; 3]>,
+    pub uv0: Vec<[f32; 2]>,
+    pub faces: Vec<TerrainFace>,
+}
+
+#[derive(Copy, Clone, Debug)]
+pub struct TerrainFace {
+    pub indices: [u16; 3],
+    pub flags: u32,
+    pub material_tag: u16,
+    pub aux_tag: u16,
+}
+
+#[derive(Clone, Debug)]
+pub struct TerrainRenderMesh {
+    pub vertices: Vec<TerrainRenderVertex>,
+    pub indices: Vec<u16>,
+    pub face_count_raw: usize,
+    pub face_count_kept: usize,
+    pub face_count_dropped_invalid: usize,
+}
+
+#[derive(Copy, Clone, Debug)]
+pub struct TerrainRenderVertex {
+    pub position: [f32; 3],
+    pub uv0: [f32; 2],
+}
+
+pub fn load_land_mesh(path: impl AsRef<Path>) -> Result<TerrainMesh> {
+    let archive = Archive::open_path(path.as_ref())?;
+
+    let positions_entry = archive
+        .entries()
+        .find(|entry| entry.meta.kind == 3)
+        .ok_or(Error::MissingChunk("type=3 (positions)"))?;
+    let uv_entry = archive.entries().find(|entry| entry.meta.kind == 5);
+    let faces_entry = archive
+        .entries()
+        .find(|entry| entry.meta.kind == 21)
+        .ok_or(Error::MissingChunk("type=21 (faces)"))?;
+
+    let positions_payload = archive.read(positions_entry.id)?.into_owned();
+    if positions_payload.len() % 12 != 0 {
+        return Err(Error::InvalidChunkSize {
+            label: "type=3 (positions)",
+            size: positions_payload.len(),
+            stride: 12,
+        });
+    }
+
+    let mut positions = Vec::with_capacity(positions_payload.len() / 12);
+    for chunk in positions_payload.chunks_exact(12) {
+        let x = f32::from_le_bytes(chunk[0..4].try_into().unwrap_or([0; 4]));
+        let y = f32::from_le_bytes(chunk[4..8].try_into().unwrap_or([0; 4]));
+        let z = f32::from_le_bytes(chunk[8..12].try_into().unwrap_or([0; 4]));
+        positions.push([x, y, z]);
+    }
+
+    let mut uv0 = vec![[0.0f32, 0.0f32]; positions.len()];
+    if let Some(uv_entry) = uv_entry {
+        let uv_payload = archive.read(uv_entry.id)?.into_owned();
+        if uv_payload.len() % 4 != 0 {
+            return Err(Error::InvalidChunkSize {
+                label: "type=5 (uv)",
+                size: uv_payload.len(),
+                stride: 4,
+            });
+        }
+        let uv_count = uv_payload.len() / 4;
+        for idx in 0..uv_count.min(uv0.len()) {
+            let off = idx * 4;
+            let u = i16::from_le_bytes([uv_payload[off], uv_payload[off + 1]]) as f32;
+            let v = i16::from_le_bytes([uv_payload[off + 2], uv_payload[off + 3]]) as f32;
+            uv0[idx] = [u / TERRAIN_UV_SCALE, v / TERRAIN_UV_SCALE];
+        }
+    }
+
+    let face_payload = archive.read(faces_entry.id)?.into_owned();
+    if face_payload.len() % 28 != 0 {
+        return Err(Error::InvalidChunkSize {
+            label: "type=21 (faces)",
+            size: face_payload.len(),
+            stride: 28,
+        });
+    }
+
+    let mut faces = Vec::with_capacity(face_payload.len() / 28);
+    for chunk in face_payload.chunks_exact(28) {
+        let flags = u32::from_le_bytes(chunk[0..4].try_into().unwrap_or([0; 4]));
+        let material_tag = u16::from_le_bytes(chunk[4..6].try_into().unwrap_or([0; 2]));
+        let aux_tag = u16::from_le_bytes(chunk[6..8].try_into().unwrap_or([0; 2]));
+        let i0 = u16::from_le_bytes(chunk[8..10].try_into().unwrap_or([0; 2]));
+        let i1 = u16::from_le_bytes(chunk[10..12].try_into().unwrap_or([0; 2]));
+        let i2 = u16::from_le_bytes(chunk[12..14].try_into().unwrap_or([0; 2]));
+        if usize::from(i0) >= positions.len()
+            || usize::from(i1) >= positions.len()
+            || usize::from(i2) >= positions.len()
+        {
+            continue;
+        }
+        faces.push(TerrainFace {
+            indices: [i0, i1, i2],
+            flags,
+            material_tag,
+            aux_tag,
+        });
+    }
+
+    Ok(TerrainMesh {
+        positions,
+        uv0,
+        faces,
+    })
+}
+
+pub fn build_render_mesh(mesh: &TerrainMesh) -> Result<TerrainRenderMesh> {
+    if mesh.positions.len() > usize::from(u16::MAX) + 1 {
+        return Err(Error::VertexCountOverflow {
+            count: mesh.positions.len(),
+        });
+    }
+
+    let vertices = mesh
+        .positions
+        .iter()
+        .enumerate()
+        .map(|(idx, &position)| TerrainRenderVertex {
+            position,
+            uv0: mesh.uv0.get(idx).copied().unwrap_or([0.0, 0.0]),
+        })
+        .collect::<Vec<_>>();
+
+    let mut indices = Vec::with_capacity(mesh.faces.len() * 3);
+    for face in &mesh.faces {
+        indices.extend_from_slice(&face.indices);
+    }
+
+    Ok(TerrainRenderMesh {
+        vertices,
+        indices,
+        face_count_raw: mesh.faces.len(),
+        face_count_kept: mesh.faces.len(),
+        face_count_dropped_invalid: 0,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use common::collect_files_recursive;
+    use std::path::{Path, PathBuf};
+
+    fn game_root() -> Option<PathBuf> {
+        let root = Path::new(env!("CARGO_MANIFEST_DIR"))
+            .join("..")
+            .join("..")
+            .join("testdata")
+            .join("Parkan - Iron Strategy");
+        root.is_dir().then_some(root)
+    }
+
+    #[test]
+    fn loads_known_land_mesh() {
+        let Some(root) = game_root() else {
+            eprintln!("skipping: game root missing");
+            return;
+        };
+
+        let land = root
+            .join("DATA")
+            .join("MAPS")
+            .join("Tut_1")
+            .join("Land.msh");
+        if !land.is_file() {
+            eprintln!("skipping missing sample {}", land.display());
+            return;
+        }
+
+        let mesh = load_land_mesh(&land)
+            .unwrap_or_else(|err| panic!("failed to parse {}: {err}", land.display()));
+        assert!(mesh.positions.len() > 1000);
+        assert!(mesh.faces.len() > 1000);
+
+        let render = build_render_mesh(&mesh).expect("failed to build render mesh");
+        assert_eq!(render.vertices.len(), mesh.positions.len());
+        assert_eq!(render.indices.len(), mesh.faces.len() * 3);
+    }
+
+    #[test]
+    fn loads_all_retail_land_meshes() {
+        let Some(root) = game_root() else {
+            eprintln!("skipping: game root missing");
+            return;
+        };
+
+        let maps_root = root.join("DATA").join("MAPS");
+        let mut files = Vec::new();
+        collect_files_recursive(&maps_root, &mut files);
+        files.sort();
+
+        let mut parsed = 0usize;
+        for path in files {
+            if !path
+                .file_name()
+                .and_then(|n| n.to_str())
+                .is_some_and(|n| n.eq_ignore_ascii_case("Land.msh"))
+            {
+                continue;
+            }
+            let mesh = load_land_mesh(&path)
+                .unwrap_or_else(|err| panic!("failed to parse {}: {err}", path.display()));
+            assert!(
+                !mesh.positions.is_empty() && !mesh.faces.is_empty(),
+                "{} parsed but empty",
+                path.display()
+            );
+            parsed += 1;
+        }
+
+        assert!(parsed > 0, "no Land.msh files parsed");
+    }
+}