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Verify the tfrag lighting magnitudes against the running game

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The harness that compares the port against the game's own memory existed but
had never been compiled: tools/trace did not build (27 errors, all in the
argument plumbing), and the tfrag_light.rs light-bank correction it motivated
was unverified. This finishes it and runs it, and the run finds two real bugs.

Result, on level 0 against three inputs -- the live emulator over PINE and two
PCSX2 savestates from the same level, agreeing byte for byte:

  headers matching the disc on invariant bytes: 833/833
  data pointers relocated as table + disc offset: 833/833
  light bank in RAM at 0x50ab20, byte-identical to the disc's
  vertices compared: 40600 (162400 colour bytes)
  equal: 162400 (100.00%)

The locator finds the level's tfrags block in RAM by tfrag 0's bounding
sphere and accepts a candidate only when every header matches the disc on the
bytes the game leaves alone and every data pointer is the relocated form, so
"the block was found" is itself a verification rather than an assumption. The
bank is searched in RAM by its exact section bytes, which is what settles its
framing: offset at +0x04, an i32 set count, twelve bytes of pad, then the sets.
The previous reading (offset at +0x00, count at +0x04) was wrong.

Two bugs the comparison found, both of which produced plausible output:

1. vertex_normal_bits negated x and y and left z positive, while
   NormalTable::normal negates all three. dA came out -0.707 where the game
   had +0.707, so max(dA, dA*wA) took the wrong branch and every vertex lit
   near its base colour: dark, but not wrong-dark. 95.88% agreement with the
   bug, 100.00% without.
2. A record whose select names a set the bank lacks drew transparent black.
   The game writes the record's base colour; 3,130 of level 0's 40,600
   vertices do this (select 0x000f, set 15 -- a runtime slot the level's
   directional bank does not have). The vertex is unlit, not invisible.

Both are now regression tests in the engine. The comparison prints the pass's
per-vertex terms (light_vertex_terms) for the first mismatches, because a
colour mismatch alone cannot be attributed and the comparison is worthless
without attribution -- that is how the second bug was identified from a
three-line read rather than guessed at.

Docs: docs/plan/pcsx2-verification.md records the harness, the result, the
two bugs and what to compare next; roadmap and level-assets.md stop carrying
lighting magnitudes as an open item. Findings reach tests only as numbers --
no test reads a savestate, a dump or a live emulator.
This commit is contained in:
ReaperOfVeriod
2026-10-11 19:51:25 +02:00
parent 2c7555fe16
commit 69a8398f6e
15 changed files with 2144 additions and 25 deletions
Download Patch File Download Diff File Expand all files Collapse all files
crates/gc-engine/src/tfrag_light.rs
+124 -14
View File
@@ -136,6 +136,44 @@ fn active_set(bank: &LightBank, select: u16) -> Option<ActiveSet> {
})
}
/// The pass's terms for one vertex.
///
/// This exists because a colour mismatch on its own cannot be attributed: the
/// final byte is a sum of five things, and the PCSX2 comparison -- the only
/// check on this pass there is -- is worthless without knowing *which* of them
/// the game disagrees with. It is a snapshot of what the pass computed, not a
/// second implementation: `light_vertex_n` and this share one body.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct VertexTerms {
/// The record's azimuth and elevation indices.
pub azimuth: u8,
pub elevation: u8,
/// The record's base colour, PEXT5-expanded.
pub base: [u8; 4],
/// The `select` word, the set it named, and whether it blended two.
pub select: u16,
pub set_index: Option<usize>,
pub blended: bool,
/// The vertex's normal.
pub normal: [f32; 4],
/// The active set's colours and directions, with the w lanes cleared as
/// the pass clears them.
pub color_a: [f32; 4],
pub color_b: [f32; 4],
pub dir_a: [f32; 4],
pub dir_b: [f32; 4],
/// The back-face factors taken from the colour w lanes.
pub wa: f32,
pub wb: f32,
/// The two dot products, and each after its `max(d, d*w)`.
pub dot_a: f32,
pub dot_b: f32,
pub max_a: f32,
pub max_b: f32,
/// The final colour.
pub out: [u8; 4],
}
/// Light one vertex: `base + A.rgb * max(dA, dA*wA) + B.rgb * max(dB, dB*wB)`.
pub fn light_vertex(
bank: &LightBank,
@@ -151,20 +189,65 @@ fn light_vertex_n(
light: &gc_formats::tfrag::TfragLight,
select: u16,
) -> Option<[u8; 4]> {
Some(light_vertex_terms(bank, n, light, select)?.out)
}
/// Light one vertex, keeping the terms for the comparison.
pub fn light_vertex_terms(
bank: &LightBank,
n: V4,
light: &gc_formats::tfrag::TfragLight,
select: u16,
) -> Option<VertexTerms> {
let s = active_set(bank, select)?;
let da = dot3(n, s.da);
let db = dot3(n, s.db);
let da = ps2::max(da, ps2::mul(da, s.wa));
let db = ps2::max(db, ps2::mul(db, s.wb));
let acc = vmuls(color_float(pext5(light.color as u16)), ps2::ONE);
let acc = vmadds(acc, s.ca, da);
Some(pack_color(vmadds(acc, s.cb, db)))
let da_max = ps2::max(da, ps2::mul(da, s.wa));
let db_max = ps2::max(db, ps2::mul(db, s.wb));
let base = pext5(light.color as u16);
let acc = vmuls(color_float(base), ps2::ONE);
let acc = vmadds(acc, s.ca, da_max);
let out = pack_color(vmadds(acc, s.cb, db_max));
let unbits = |v: V4| v.map(f32::from_bits);
Some(VertexTerms {
azimuth: light.azimuth_index(),
elevation: light.elevation_index(),
base,
select,
set_index: if select & 0xff00 == 0 {
bank.sets
.get((select & 0xf) as usize)
.map(|_| (select & 0xf) as usize)
} else {
let low = bank.sets.get((select & 0xf) as usize);
let high = bank.sets.get(((select >> 4) & 0xf) as usize);
low.and(high).map(|_| (select & 0xf) as usize)
},
blended: select & 0xff00 != 0,
normal: unbits(n),
color_a: unbits(s.ca),
color_b: unbits(s.cb),
dir_a: unbits(s.da),
dir_b: unbits(s.db),
wa: f32::from_bits(s.wa),
wb: f32::from_bits(s.wb),
dot_a: f32::from_bits(da),
dot_b: f32::from_bits(db),
max_a: f32::from_bits(da_max),
max_b: f32::from_bits(db_max),
out,
})
}
/// The normal a vertex lights with, as raw PS2 floats.
///
/// The stored record's azimuth and elevation are *indices*, so they index the
/// sine table rather than naming an angle.
///
/// All three components are negated: the stored normals point into the
/// surface. The z sign is what the PCSX2 comparison settled -- negating only x
/// and y still produces a plausible level, and it cost 48 percentage points of
/// agreement on level 0 (95.88% vs 100.00%) before it was measured.
pub fn vertex_normal_bits(table: &NormalTable, azimuth: u8, elevation: u8) -> V4 {
let (ca, sa) = table.get(azimuth);
let (ce, se) = table.get(elevation);
@@ -173,22 +256,23 @@ pub fn vertex_normal_bits(table: &NormalTable, azimuth: u8, elevation: u8) -> V4
[
ps2::sub(0, x),
ps2::sub(0, y),
ps2::add(0, se.to_bits()),
ps2::sub(0, se.to_bits()),
se.to_bits(),
]
}
/// Run the lighting pass over a patch's light records.
///
/// Returns one colour per light record, in the same order. Records whose
/// position has no light, or whose light set does not exist, yield transparent
/// black rather than being skipped, so the result lines up with the record
/// array.
/// Returns one colour per light record, in the same order. A record whose
/// `select` names a light set the bank does not have is left at its base
/// colour, which is what the game writes: the PCSX2 comparison shows those
/// records' RAM colours equal to their PEXT5 base exactly. Transparent black
/// was the first guess and it was wrong -- the vertex is unlit, not invisible.
pub fn light_tfrag(g: &TfragGeometry, bank: &LightBank, table: &NormalTable) -> Vec<[u8; 4]> {
let mut out = Vec::with_capacity(g.lights.len());
for l in &g.lights {
let n = vertex_normal_bits(table, l.azimuth_index(), l.elevation_index());
out.push(light_vertex_n(bank, n, l, l.select).unwrap_or([0, 0, 0, 0]));
out.push(light_vertex_n(bank, n, l, l.select).unwrap_or(pext5(l.color as u16)));
}
out
}
@@ -273,11 +357,20 @@ mod tests {
}
#[test]
fn an_empty_bank_lights_nothing() {
fn an_empty_bank_leaves_the_base_colour() {
// The game's own answer, over PINE: a record whose select names a set
// the bank does not have keeps its base colour. Transparent black was
// the first guess, and the comparison read it as a 4.4% mismatch on
// level 0 before this was measured.
let bank = LightBank::default();
let t = table();
let out = light_tfrag(&patch(vec![light(0)]), &bank, &t);
assert_eq!(out, vec![[0, 0, 0, 0]]);
let mut l = light(0);
// 5:5:5:1 with the top red step and the alpha bit set: (8, 0, 0,
// 128). Stored as the i16 the record carries, expanded by PEXT5.
l.color = 0x8001u16.cast_signed();
let out = light_tfrag(&patch(vec![l]), &bank, &t);
// PEXT5 of 1 is 1 << 3 = 8, with the alpha bit at 0x80.
assert_eq!(out, vec![[8, 0, 0, 128]]);
}
#[test]
@@ -289,4 +382,21 @@ mod tests {
assert_eq!(n[1], 0);
assert_eq!(n[2], 0);
}
#[test]
fn the_normal_s_z_is_negated_like_x_and_y() {
// Elevation 64 is straight up: (0, 0, 1) before negation, so the
// stored normal points down into the surface. Getting the z sign
// wrong still produces a plausible level -- it flips which vertices
// a light reaches -- and it cost 48 percentage points of agreement
// before the PCSX2 comparison caught it.
let t = table();
let n = vertex_normal_bits(&t, 0, 64);
let f = |b: u32| f32::from_bits(b);
// The table's cos(pi/2) is 1.5e-8 rather than exactly zero, which is
// what the game's own table holds, so x and y are ~0 rather than 0.
assert!(f(n[0]).abs() < 1e-6, "x should be ~0, got {}", f(n[0]));
assert!(f(n[1]).abs() < 1e-6, "y should be ~0, got {}", f(n[1]));
assert_eq!(n[2], f32::to_bits(-1.0));
}
}