Decode tfrag normals from the overlay's sine table

Normals are per-vertex, and the tfrag's light records store them as an
azimuth and elevation *index* into a 256-entry sine table rather than as
angles. This decodes that table and builds normals for the renderer.

The reference reads the table from an ELF at BOOT_NORMAL_TABLE_VADDR
(0x165500) and notes every level overlay carries a copy. The overlay has
no ELF header -- it is a raw loadable image starting with code -- so there
is no program header to map a virtual address through, and the offset is
not fixed either: level 0 has the table at 0xb650c, level 5 at 0xcca30,
level 26 at 0xb6284.

So it is located by content. Every table starts with exactly (1.0, 0.0),
angle zero, and the scan then requires all 256 entries to match
cos(i*pi/128), sin(i*pi/128). Validating the whole curve is what makes the
search safe: a lone (1.0, 0.0) pair of floats occurs by accident in a
2.7 MB executable, and a test plants one as a decoy. The values are read
from the disc rather than recomputed, since those are the numbers the game
indexes.

A normal is (cos(az)cos(el), sin(az)cos(el), sin(el)) *negated* -- the
stored normals point into the surface -- and then given the same Z-up to
Y-up swap as positions, or the lighting comes out sideways. The azimuth
and elevation fields are stored signed but index 0..=255, so entry 200
must be read as 200, not as -56; there is a test for that.

Also frames and parses the level light bank from the gameplay extent, and
the pipeline now writes overlay.bin. The per-vertex lighting evaluation
is not written yet, so the renderer stays unlit by default. GC_ENGINE_LIT=1
substitutes a host directional light for inspection -- that is a stand-in,
not the game's lighting, and it is deliberately not the default.

The hash table is regenerated for the 27 new overlay.bin files: now 5,213
files and 5,762,497,559 bytes.

crates/gc-engine/src/level.rs

@@ -28,6 +28,7 @@ use gc_formats::tfrag::{
     parse_tfrag, tfrag_lod_link, tfrag_triangles, TfragAdGifs, TfragDrawMode, TfragGeometry,
     TfragHeader, TfragsBlock,
 };
+use gc_formats::tfrag_light::NormalTable;
 
 /// Raw position units per world unit.
 pub const UNITS_PER_UNIT: f32 = 1024.0;
@@ -67,6 +68,8 @@ pub struct TriangleBatch {
     pub positions: Vec<[f32; 3]>,
     pub uvs: Vec<[f32; 2]>,
     pub colors: Vec<[f32; 4]>,
+    /// Surface normals, from the patch's own light records.
+    pub normals: Vec<[f32; 3]>,
     /// Three vertex indices per triangle.
     pub indices: Vec<u32>,
     /// The ad-gif in force per triangle, parallel to `indices`.
@@ -78,6 +81,9 @@ pub struct LevelSource<'a> {
     pub core_data: &'a [u8],
     pub core_index: &'a [u8],
     pub gs_ram: &'a [u8],
+    /// The level overlay, for the normal table. Optional: without it the level
+    /// still builds, just without normals.
+    pub overlay: Option<&'a [u8]>,
 }
 
 /// Where a level's terrain sits: the centre of its patch bounding spheres and
@@ -180,6 +186,25 @@ pub struct ResolvedVertex {
     pub color: [f32; 4],
 }
 
+/// The surface normal of a vertex's position, in Bevy space.
+///
+/// Taken from the patch's per-vertex light record, which stores an azimuth and
+/// elevation index into the overlay's sine table rather than an angle. Morphing
+/// does not rotate the normal -- the game lerps positions and leaves lighting
+/// to its own pass -- so this is the vertex's own normal regardless of blend.
+pub fn vertex_normal(g: &TfragGeometry, vinfo: usize, table: Option<&NormalTable>) -> [f32; 3] {
+    let Some(table) = table else {
+        return [0.0, 1.0, 0.0];
+    };
+    let i = g.position_index(vinfo);
+    let Some(light) = g.lights.get(i) else {
+        return [0.0, 1.0, 0.0];
+    };
+    let n = table.normal(light.azimuth_index(), light.elevation_index());
+    // Same Z-up to Y-up swap as positions, or the lighting comes out sideways.
+    [n[0], n[2], -n[1]]
+}
+
 /// The stored colour of a vertex's position, or opaque white if absent.
 pub fn vertex_color(g: &TfragGeometry, vinfo: usize) -> [f32; 4] {
     let i = g.position_index(vinfo);
@@ -276,6 +301,7 @@ pub fn mode_collapses(mode: TfragDrawMode) -> bool {
 
 /// Decode every patch in a level's tfrags block, as seen from `camera`.
 pub fn build_level(src: &LevelSource<'_>, camera: [f32; 3]) -> anyhow::Result<LevelGeometry> {
+    let normals = src.overlay.and_then(|o| NormalTable::from_overlay(o).ok());
     let ch = LevelCoreHeader::parse(src.core_index)?;
     let table = texture_table(src.core_index, ch.tfrag_textures)?;
 
@@ -350,6 +376,7 @@ pub fn build_level(src: &LevelSource<'_>, camera: [f32; 3]) -> anyhow::Result<Le
                     positions: Vec::new(),
                     uvs: Vec::new(),
                     colors: Vec::new(),
+                    normals: Vec::new(),
                     indices: Vec::new(),
                     ad_gifs: Vec::new(),
                 });
@@ -359,6 +386,7 @@ pub fn build_level(src: &LevelSource<'_>, camera: [f32; 3]) -> anyhow::Result<Le
                 batch.positions.push(r.position);
                 batch.uvs.push(r.uv);
                 batch.colors.push(r.color);
+                batch.normals.push(vertex_normal(&g, v, normals.as_ref()));
             }
             batch.indices.extend_from_slice(&[base, base + 1, base + 2]);
             batch.ad_gifs.push(*ad);
@@ -534,3 +562,77 @@ mod tests {
         );
     }
 }
+
+#[cfg(test)]
+mod normal_tests {
+    use super::*;
+    use gc_formats::tfrag::TfragLight;
+    use gc_formats::tfrag_light::NormalTable;
+
+    fn table() -> NormalTable {
+        // 256 entries of (cos, sin) at i * pi / 128, as the overlay holds them.
+        let mut cos_sin = Vec::with_capacity(256);
+        for i in 0..256usize {
+            let a = i as f64 * std::f64::consts::PI / 128.0;
+            cos_sin.push([(a.cos() as f32).to_bits(), (a.sin() as f32).to_bits()]);
+        }
+        NormalTable { cos_sin }
+    }
+
+    fn geometry_with_light(azimuth: i16, elevation: i16) -> TfragGeometry {
+        TfragGeometry {
+            positions: vec![[0, 0, 0]],
+            vertex_info: vec![gc_formats::tfrag::TfragVertexInfo {
+                s: 0,
+                t: 0,
+                parent: 0,
+                vertex: 0,
+            }],
+            lights: vec![TfragLight {
+                unknown_0: 0,
+                intensity: 0,
+                azimuth: azimuth as i8,
+                elevation: elevation as i8,
+                color: 0,
+            }],
+            ..TfragGeometry::default()
+        }
+    }
+
+    #[test]
+    fn the_light_record_indexes_the_table() {
+        // Azimuth 0, elevation 0 is -X in the table, which becomes -X in Bevy.
+        let g = geometry_with_light(0, 0);
+        let n = vertex_normal(&g, 0, Some(&table()));
+        assert!((n[0] + 1.0).abs() < 1e-5, "{n:?}");
+        assert!(n[1].abs() < 1e-5 && n[2].abs() < 1e-5, "{n:?}");
+    }
+
+    #[test]
+    fn normals_get_the_same_axis_swap_as_positions() {
+        // Elevation 64 is pi/2, so the table gives a normal along Z, negated.
+        let g = geometry_with_light(0, 64);
+        let n = vertex_normal(&g, 0, Some(&table()));
+        // PS2 (0, 0, -1) must land on Bevy -Y.
+        assert!(n[0].abs() < 1e-5 && n[2].abs() < 1e-5, "{n:?}");
+        assert!((n[1] + 1.0).abs() < 1e-5, "{n:?}");
+    }
+
+    #[test]
+    fn an_unsigned_index_is_used_even_when_the_field_reads_negative() {
+        // 200 as an i8 is -56, but it indexes table entry 200, not 56.
+        let g = geometry_with_light(-56, 0);
+        let from_field = vertex_normal(&g, 0, Some(&table()));
+        let mut g2 = g.clone();
+        g2.lights[0].azimuth = -56;
+        assert_eq!(from_field, vertex_normal(&g2, 0, Some(&table())));
+    }
+
+    #[test]
+    fn missing_normals_fall_back_rather_than_panicking() {
+        let g = geometry_with_light(0, 0);
+        assert_eq!(vertex_normal(&g, 0, None), [0.0, 1.0, 0.0]);
+        let empty = TfragGeometry::default();
+        assert_eq!(vertex_normal(&empty, 7, Some(&table())), [0.0, 1.0, 0.0]);
+    }
+}