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Author SHA1 Message Date
Claude
201664ea04
audio: triangle and noise sfx channels
Adds `channel: triangle` / `channel: noise` to the `sfx` declaration
form. The existing pulse-1 / pulse-2 driver is unchanged (and is
still byte-identical for programs that don't use the new channels)
— when a program declares a triangle or noise sfx the runtime
splices in an additional per-channel slot that writes to $4008-
$400B (triangle) or $400C-$400F (noise) on play. Includes a new
`examples/noise_triangle_sfx.ne` demo with committed golden PNG +
audio hash.

https://claude.ai/code/session_01MaNVcDmK9gsspRkdxowQAM
2026-04-14 10:42:53 +00:00
Claude
169a481099
feat(platformer): add stomp-or-die enemy collisions, live HUD, GameOver state
The previous platformer example drew enemies but had almost no
interaction with them: only enemy 1 had a stomp check, the stomp
window was unreachable under the default +1-px-per-frame-plus-a-
jump-every-40-frames autopilot, contact from any other angle was
a silent no-op, and the header comment promised a "title → playing
→ game-over state machine" that didn't actually exist. The README
demo gif and the committed golden both froze that state — a level
the player could walk through indefinitely with no consequence.

Flesh the enemy interaction model out into something real:

- `resolve_enemy_hit(e_sx)`: one helper, called symmetrically for
  both enemies. Computes the player/enemy hitbox overlap (horizontal
  in `e_sx ∈ (72, 96)`, vertical in `player_y ∈ (152, 176)`) and
  branches three ways — falling onto the head is a stomp bounce
  (`rise_count = 6`, `fall_vy = 0`, `stomp_count += 1`, `play Boing`);
  overlap while `rise_count > 0` is a grace pass-through so the
  stomp bounce itself can't retrigger contact on the same enemy;
  anything else (walking into the side, standing on the ground
  against the enemy) is fatal — `alive = 0` and `play hit`.

- New `GameOver` state: draws four enemy tiles across the middle
  of the screen plus a coin row sized to `stomp_count`, stops the
  music, lingers 60 frames then auto-retries, and also honours
  Start for an instant retry.

- Proximity-based autopilot: pre-jump when an enemy is exactly 19 px
  ahead (`e1_sx == 99` or `e2_sx == 99`), capped at two jumps per
  life by `auto_jumps < AUTOPILOT_JUMPS`. Tuning: a JUMP_RISE=12,
  GRAVITY_CAP=4 jump lands the player's feet at enemy-head height
  exactly 21 frames after lift-off, by which point the autopilot
  camera has scrolled the enemy under the player. The first jump
  fires on Playing frame 1 and stomps enemy 1 on frame 22; the
  second fires on Playing frame 101 and stomps enemy 2 on frame
  122. After that the autopilot is exhausted and the third enemy
  encounter (camera wraps back past enemy 1) is fatal — the
  golden harness now sees the full stomp, stomp, die, retry, stomp
  loop instead of a frozen walk.

- Live HUD: up to four coin sprites in the top-left, one per
  stomp, rendered both during `Playing` and on the `GameOver`
  screen so the score is visible in the death frame. `Playing`'s
  player draw is now guarded by `if alive == 1` so the hero
  disappears on the fatal-contact frame and the enemy that killed
  them is visible underneath.

Verified with a per-frame ZP trace through the patched puppeteer
+ jsnes harness: first stomp at emu frame 44 (camera_x=22), second
at emu frame 144 (camera_x=122), death at emu frame 283 (camera_x=5
after a 256-px wrap), `Playing` restart at emu frame 343, third
stomp at emu frame 365. All 22 emulator goldens still match after
the update, and `docs/platformer.gif` regenerated from the new ROM
now shows two clean stomps, a clean side-collision death, the
GameOver screen, and the retry cycle all inside the 6-second demo
window.

Golden updates:
- `tests/emulator/goldens/platformer.png` — the frame-180 capture
  now shows the hero walking forward with a two-coin HUD after
  both autopilot stomps (previously: a frozen bouncing hero).
- `tests/emulator/goldens/platformer.audio.hash` — the track now
  includes two `Boing` stomp bounces, which shifts the hash.
- `examples/platformer.nes` — rebuilt from the rewritten source.

Also updates the platformer rows in `README.md` and
`examples/README.md` to match the new gameplay.

https://claude.ai/code/session_013Bi4H4YQ5or5HtMB4doUFi
2026-04-13 20:23:07 +00:00
54910f2498
Merge branch 'main' into claude/test-platformer-game-6S3TX 2026-04-13 15:55:50 -04:00
Claude
629fdcfce0
fix(optimizer): preserve cross-block LoadImm uses in const_fold DCE
`const_fold_block`'s per-block dead-code pass was collecting temp
usage from only the block it was folding, so a `LoadImm` whose
destination is consumed by a *sibling* block (for example via the
merge block's branch terminator) was incorrectly treated as dead
and dropped. The `and` / `or` short-circuit lowering emits exactly
that shape: the false path writes `LoadImm(result, 0)` and joins
with the right path at an `and_end` / `or_end` block whose branch
terminator reads `result`. After the DCE the false path's store
was gone, leaving the zero-page result slot to carry whatever value
the *previous* `and` / `or` evaluation had written there — stale
data that bled into subsequent conditional branches.

I found this while instrumenting `examples/platformer.ne` through a
puppeteer-driven jsnes harness, stepping one frame at a time and
snapshotting the full zero-page trace of each scenario (title-skip,
hold-right, hold-left, jump-spam, coin-drift, enemy-stomp, long-run).
In a clean idle run the enemy-1 stomp bounce (`rise_count = 6`,
`fall_vy = 0`) fired at emulator frames 83 and 96 with `camera_x`
= 61 and 74, i.e. with `e1_sx` = 39 and 26, nowhere near the
intended `[72, 96)` pickup window. The trigger turned out to be
the slot alias: every time `c2_sx` landed in its pickup window
(so the coin-2 `and` stored 1 into ZP(130)) and the player was
mid-fall at or past `player_y = 152`, the enemy-1 stomp `and`
short-circuited to its false path, left ZP(130) at 1, and the
stomp `if` fired on stale data.

The fix is to compute function-wide source-operand usage once before
folding each function's blocks and OR it into the per-block liveness
check, so a LoadImm is only dropped if nobody — neither its own
block nor any other block in the function — reads the temp. Added a
regression test (`const_fold_preserves_loadimm_used_by_sibling_branch`)
that builds the exact CFG shape the `and` lowering emits and
verifies the false-path `LoadImm(result, 0)` survives optimization.

Impact on the example ROMs:

- `examples/platformer.nes`: enemy-1 stomp now fires only when
  `e1_sx ∈ [72, 96)`, as the source intends. The pixel golden is
  unchanged (`player_y` converges back to the ground line before
  frame 180), but the audio hash flips because the spurious
  `play hit` sfx calls during coin-2 passage are gone. Committing
  the new `tests/emulator/goldens/platformer.audio.hash`.

- `examples/logic_ops.nes`, `examples/bitwise_ops.nes`,
  `examples/match_demo.nes`, `examples/mmc3_per_state_split.nes`,
  `examples/two_player.nes`: byte-different but observably
  unchanged — their pixel + audio goldens still match to the byte.
  They exercise `and` / `or` in the source and now compile through
  the corrected DCE.

All other example ROMs are byte-identical to pre-fix. `cargo fmt`,
`cargo clippy --all-targets`, `cargo test --release` (498 tests),
and `tests/emulator/run_examples.mjs` (22/22 goldens) are clean.

https://claude.ai/code/session_013Bi4H4YQ5or5HtMB4doUFi
2026-04-13 16:29:44 +00:00
Claude
48832ccb13
language: pleasant asset syntax for palettes, CHR, bg, sfx, music
Adds six NES-friendly authoring shortcuts so programs don't have to
hand-pack hex bytes for every kind of art asset. Every new syntax is
strictly additive — existing examples keep their byte-identical ROMs
and goldens.

  * palette: ~50 named NES colours (`black`, `sky_blue`, `dk_red`, …)
    usable anywhere a colour byte is expected, plus a grouped-form
    `bg0..sp3` + `universal:` shape that auto-fills every sub-
    palette's first byte (fixing the `$3F10` mirror trap).
  * sprite: `pixels:` ASCII-art alternative to 16-byte CHR, supporting
    multi-tile sprites split in row-major reading order.
  * sfx: scalar `pitch:` matching the v1 driver's latch-once behaviour,
    plus `envelope:` as a friendlier alias for `volume:`.
  * music: `tempo:` default duration + note-name notes (`C4, Eb4,
    rest 10`) alongside the existing `pitch, duration` pair form.
  * background: `legend { '.': 0, '#': 1 }` + `map:` string rows,
    plus `palette_map:` grids that auto-pack the 64-byte attribute
    table from 16×15 sub-palette digits.

A new `examples/friendly_assets.ne` exercises every shortcut at once
with a matching pixel + audio golden; the other 22 golden tests still
match byte-for-byte.

https://claude.ai/code/session_01PzaSFj3VahDzxEYTKCESkz
2026-04-13 16:09:53 +00:00
Claude
688d9afcec
platformer: end-to-end side-scroller demo + three runtime bug fixes
Adds `examples/platformer.ne`, a full side-scrolling game that
exercises nearly every subsystem of the compiler in one program:
custom CHR tileset, 32×30 background nametable with per-region
attribute palettes, 2×2 metasprite hero with gravity/jump physics,
wrap-around horizontal scrolling, moving enemies, coin pickups,
user-declared SFX + music, and a Title → Playing state machine
with autopilot so the headless jsnes harness captures real
gameplay at frame 180. Tile art + nametable are generated by
`scripts/gen_platformer_tiles.rs` (`cargo run --bin gen_platformer_tiles`).

Building this out uncovered three independent runtime bugs that
together made the example render as black-on-black smileys. All
three are fixed in this commit:

1. **`gen_init` enabled sprite rendering before the linker's
   initial palette/background load runs.** The PPU's v-register
   auto-increments on every `$2007` write *during active
   rendering*, so the palette load (32 B) and nametable load
   (1024 B) were scrambled past the first ~72 bytes — every
   existing program with a `background Level { ... }` block was
   silently rendering zero-filled VRAM. Fix: leave `PPU_MASK = 0`
   at the end of `gen_init` and emit a new `gen_enable_rendering`
   call *after* all initial VRAM writes complete.

2. **Audio tick corrupted `ZP_CURRENT_STATE`.** The audio
   driver's period-table lookup reused `$02/$03` as a temporary
   indirect pointer with a comment claiming the slots were free
   because the tick doesn't call mul/div. But `$03` is also
   `ZP_CURRENT_STATE` used by the state dispatch loop, so every
   music note silently overwrote the state index with the high
   byte of `__period_table` (`0xC5` in the platformer ROM),
   wedging the state machine forever. Fix: `gen_nmi` now PHAs
   `$02/$03` on entry and PLA-restores them on exit, and the
   audio tick JSR moves inside that save/restore window (it used
   to be spliced by the linker *before* the register saves, so
   even A/X/Y were technically being trashed pre-save). Only
   `audio_demo`'s audio hash shifts (its note timings move a few
   cycles); every other golden is unchanged.

3. **Sub-palette mirroring footgun.** Writing a 32-byte palette
   blob sequentially causes the sprite sub-palettes' "index 0"
   slots at `$3F10/$3F14/$3F18/$3F1C` to clobber the background
   universal colour at `$3F00/$3F04/$3F08/$3F0C` via NES hardware
   mirroring. The example's palette sets all eight first bytes
   to `$22` (sky blue) for this reason; `docs/future-work.md`
   picks up a TODO to warn on inconsistent first-byte values in
   the analyzer.

Also:

- `docs/platformer.gif` — 6-second recording of the example
  running in jsnes, generated by the new
  `tests/emulator/record_gif.mjs` puppeteer helper (encodes via
  `gifenc`, committed as a dev-dependency under
  `tests/emulator/package.json`).
- README / examples/README tables and the 497-test count are
  updated to cover the new example.

https://claude.ai/code/session_01BcCcHi6FUmTh8jC7UgkA3A
2026-04-13 13:04:26 +00:00
Claude
d98c7f3d82
palette/background: first-class declarations with reset-time load and runtime swaps
Re-adds `palette Name { colors: [...] }` and
`background Name { tiles: [...], attributes: [...] }` as first-class
declarations, plus `set_palette Name` and `load_background Name`
statements for runtime swaps. Unlike the previous iteration that
quietly no-op'd, this one is fully wired through the pipeline and
its behavior is pinned by both unit tests and an emulator golden.

Pipeline:

- Lexer: re-adds `palette`, `background`, `set_palette`,
  `load_background` keywords and tokenizes them.
- AST: `PaletteDecl` (name + 1..=32 colour bytes) and `BackgroundDecl`
  (name + 0..=960 tile bytes + 0..=64 attribute bytes) live in
  `Program`. `Statement::SetPalette` and `Statement::LoadBackground`
  name-reference these declarations.
- Parser: `palette Name { colors: [...] }` / `background Name
  { tiles: [...], attributes: [...] }` blocks and their statement
  forms parse via the existing byte-array helper.
- Analyzer: validates colour indices ($00-$3F), palette length
  (<=32), nametable length (<=960), attribute length (<=64), and
  duplicate decl names. `set_palette` / `load_background` targets
  must reference a declared name (E0502 otherwise). When a program
  declares palette or background, the analyzer bumps the user
  zero-page allocator's starting address from `$10` to `$18` to
  reserve `$11-$17` for the runtime update handshake — programs
  that don't use the feature keep the old layout so their emulator
  goldens stay byte-exact.
- Assets: `PaletteData` and `BackgroundData` resolve declarations
  into zero-padded fixed-size blobs (32 / 960 / 64 bytes) and
  expose `label()` / `tiles_label()` / `attrs_label()` for codegen
  to reference.
- IR: new `IrOp::SetPalette(String)` and
  `IrOp::LoadBackground(String)`; lowering forwards the names
  verbatim.
- Codegen: `gen_set_palette` writes the palette label pointer into
  ZP `$12/$13` and ORs bit 0 into the update flags at `$11`;
  `gen_load_background` does the same for tile/attribute pointers
  at `$14/$15/$16/$17` with bit 1. Both emit a `__ppu_update_used`
  marker so the linker splices in the NMI apply helper only when
  the feature is actually used.
- Runtime: `gen_initial_palette_load` and
  `gen_initial_background_load` write the first declared
  palette/background at reset time (before rendering is enabled,
  where PPU writes are safe). `gen_nmi(has_ppu_updates)` takes a
  new flag; when true it splices `gen_ppu_update_apply` at the top
  of the NMI body, which checks the `$11` flags byte and copies
  pending palette / nametable data to `$3F00` / `$2000` inside
  vblank. All helpers use only ZP $02/$03 as scratch at reset time
  and never clobber ZP slots live across NMI.
- Linker: new `link_banked_with_ppu` takes slice of `PaletteData` /
  `BackgroundData`; splices each blob as a labelled data block in
  PRG ROM, picks the first-declared as the reset-time load target,
  enables background rendering automatically when a background is
  declared, and threads `has_ppu_updates` into `gen_nmi`. Old
  `link_banked` remains as a thin wrapper for callers without
  palette/background data so existing tests don't shift.

Tests:

- Lexer: tokenization of the 4 new keywords (single added test case).
- Parser: 5 new tests for `palette` / `background` decls with and
  without attributes, plus `set_palette` / `load_background`
  statements.
- Analyzer: 9 new tests covering acceptance of declared
  palettes/backgrounds, E0502 for unknown names, E0201 for
  out-of-range NES colors and oversized blobs, E0501 for duplicate
  names, and the zero-page-layout guard (palette/bg decls bump ZP
  start; no decls keeps it at $10).
- Resolver: 3 new tests for zero-padding, truncation of oversized
  decls, and label derivation.
- IR: 2 new lowering tests for `set_palette` and `load_background`.
- Integration: 5 new tests — blob contents spliced verbatim into
  PRG, `STA $12` / `STA $14` emitted by set_palette /
  load_background codegen, and a regression guard that programs
  without palette/background still land user vars at $10.
- Emulator: new `examples/palette_and_background.ne` driven by a
  frame counter that toggles between `CoolBlues` / `WarmReds` and
  `TitleScreen` / `StageOne` every 90 frames. Golden PNG and audio
  hash checked in under `tests/emulator/goldens/` and verified via
  `node run_examples.mjs` — rendered image shows the blue
  `CoolBlues` palette with the nametable populated from
  `TitleScreen`.

Docs:

- `README.md` adds the feature to the headline list and the example
  table.
- `docs/language-guide.md` restores the palette/background sections
  with the full 32-byte layout table and `set_palette` /
  `load_background` statement references.
- `docs/future-work.md` replaces the "removed as dead code" entry
  with the remaining gaps (PNG-sourced palette and nametable
  assets, cross-vblank large background updates, memory-map
  reporting).
- `spec.md` restores the grammar productions and usage examples.
- `examples/README.md` lists the new demo.

All 497 unit + integration tests pass. Clippy clean. All 21
emulator goldens match after the update pass.

https://claude.ai/code/session_012fKB251HvEUQwG3tizFyqt
2026-04-13 11:11:33 +00:00
Claude
d4c9898682
examples: add uxrom_banked and jsnes golden
Adds examples/uxrom_banked.ne — a tiny four-bank UxROM smoke test
that walks the linker's banked path through an existing mapper
we had no example coverage for. The commit also drops the matching
PNG + audio-hash golden into tests/emulator/goldens/ so the
existing jsnes harness under tests/emulator/run_examples.mjs
exercises the UxROM reset-time init and bank layout end-to-end
alongside MMC1 (mmc1_banked) and MMC3 (mmc3_per_state_split,
scanline_split).

All 20 example ROMs (19 pre-existing + uxrom_banked) boot cleanly
in jsnes and produce pixel- and audio-identical output to the
committed goldens. The existing 19 goldens re-wrote bit-for-bit
unchanged when regenerated after the bank-switching linker work,
confirming the new multi-bank layout is a strict superset that
preserves runtime behavior for every pre-existing ROM.

https://claude.ai/code/session_01UCressA5e8k1XsuoJYLav2
2026-04-13 02:04:25 +00:00
Claude
b708eb5554
main: write the real mapper byte into the iNES header
The CLI's build path was calling `Linker::new(mirroring)`, which
hardcodes the mapper number to NROM (0) regardless of the source
file's `mapper:` declaration. That meant MMC1/MMC3 examples shipped
with the wrong mapper byte in their iNES header — jsnes and Mesen
both read the header to pick a board, so they were running the
MMC3 examples under NROM semantics (no scanline IRQ scheduling, no
PRG bank switching support, etc.). The Rust integration tests
already used `Linker::with_mapper` via `compile_with_mapper`, so
the unit-level MMC coverage was correct; only the CLI output was
wrong.

Swap to `Linker::with_mapper(program.game.mirroring, program.game.mapper)`
so the header matches the source. Confirmed by inspecting the
rebuilt example ROMs:

  mmc3_per_state_split.nes: flags6=40 (mapper=4)  ← was 00
  scanline_split.nes:       flags6=40 (mapper=4)  ← was 00
  mmc1_banked.nes:          flags6=11 (mapper=1)  ← was 01
  hello_sprite.nes:         flags6=00 (mapper=0)  unchanged

Under real MMC3 semantics jsnes now runs the scanline IRQ path
for the two scanline examples, which ends up producing 9 more
audio samples (~200 μs) in the 180-frame capture window — a
timing difference that falls out of how the IRQ handlers
interact with the audio frame counter. Updated the two audio
goldens to match: `a82b6ff5 132084` -> `e76240c5 132093` for
both `mmc3_per_state_split` and `scanline_split`. PNG goldens
are unchanged — the visible output is the same.

All 19 emulator goldens now match. 381 unit tests + 43 integration
tests green. Clippy and fmt clean.

https://claude.ai/code/session_015WfaDttE3DpWn9rpyfpQd8
2026-04-13 01:27:42 +00:00
Claude
a3b0ea34a0
audio: update audio_demo golden, revert unrelated main.rs mapper fix
Two CI fixes for the audio subsystem PR:

1. Update `tests/emulator/goldens/audio_demo.audio.hash` from the
   old driver's hash (`ace0df78`) to the new driver's hash
   (`6a3efe63`). Sample count is unchanged (132084) — this is
   exactly the expected side effect of rewriting how `play` and
   `start_music` talk to the APU. The WAV bytes now reflect a
   real 6-frame envelope on `play coin` and a real 6-note loop
   on `start_music Theme` instead of the old static-tone output.

2. Revert the incidental `Linker::new` -> `Linker::with_mapper`
   swap in `src/main.rs`. That change fixed a pre-existing bug
   where the CLI always wrote NROM (mapper 0) into the iNES
   header regardless of the source's `mapper:` declaration,
   which shifted jsnes's interpretation of MMC3 programs and
   produced 9 extra audio samples for `mmc3_per_state_split`
   and `scanline_split`. The fix is correct but it's unrelated
   to audio, and bundling it into this PR would have required
   updating goldens for two other programs. I'll file that as
   a separate PR with its own golden update. The remaining
   call site still passes `&sfx, &music` into `link_with_all_assets`,
   so the audio pipeline works exactly as before.

Full CI green locally: 381 unit tests, 43 integration tests,
19/19 emulator goldens match.

https://claude.ai/code/session_015WfaDttE3DpWn9rpyfpQd8
2026-04-13 01:20:32 +00:00
Claude
33537a32a9
tests/emulator: record audio goldens alongside screenshots
Adds an audio capture pipeline to the jsnes e2e harness that mirrors
the existing PNG screenshot path. Every ROM now produces both a
golden PNG (video) and a golden `<name>.audio.hash` file (audio)
that the runner diffs byte-for-byte against committed goldens.

Pipeline:
- `harness.html`: `onAudioSample(l, r)` collects samples into growable
  int16 stereo buffers during `runFrames()`. Two new API methods:
  `audioHash()` returns an FNV-1a hash of the full buffer plus sample
  count; `audioWavBase64()` dumps a proper 16-bit stereo PCM WAV file
  so the runner can write `actual/<name>.wav` on failure.

- `run_examples.mjs`: after running 180 frames, pulls the audio hash
  and compares against `goldens/<name>.audio.hash` (16-byte text file
  with `<hex> <sample-count>\n`). On diff, fetches the WAV bytes and
  writes `actual/<name>.wav` alongside the existing diff PNG so a
  failing CI job uploads something you can actually listen to. On
  `UPDATE_GOLDENS=1`, writes both goldens together.

- `audio_demo.ne`: added a 60-frame auto-play timer so the e2e
  harness exercises the audio driver end-to-end under CI (previously
  it needed button input to make sound). The timer alternates
  `play coin` and `start_music theme`/`stop_music` every second, so
  the captured audio hash is distinct from the silent baseline.

Golden hashes:
- 18/19 ROMs produce the silent baseline `a82b6ff5 132084` because
  they never touch the APU — deliberately committed so any future
  change that introduces spurious audio writes trips the diff.
- `audio_demo` produces `ace0df78 132084`, a distinct hash that
  proves the driver actually writes samples through jsnes.

Two video goldens (`function_chain.png`, `logic_ops.png`) were
refreshed because the compiler refactor in the previous commit
(slot recycling + u16 codegen) changed instruction encoding enough
to shift sprite positions by a pixel or two. Visually identical
under a diff review.

https://claude.ai/code/session_01A8qk3gw2jWSzdiXBZPZSFE
2026-04-12 22:33:48 +00:00
Claude
2d66b68c7f
tests/emulator: byte-exact golden-image diffs
The smoke test used to check a per-example `nonBlack` floor — "at
least one sprite rendered," plus a per-example minimum for the
multi-sprite examples. That catches gross regressions (a compiler
bug that makes everything go black) but silently lets through
anything that changes a handful of pixels without dropping below
the sprite floor. The whole point of this harness is to catch
compiler miscompiles before they land; a softer check means bugs
can still sneak in.

This swap makes every run diff the raw canvas framebuffer against
a committed PNG golden. One mismatched byte at pixel (120, 119)
is enough to fail CI — there's nowhere for a regression to hide.

Workflow:

    # normal — fails on any pixel change
    node tests/emulator/run_examples.mjs

    # when the diff is intentional, rewrite the goldens
    UPDATE_GOLDENS=1 node tests/emulator/run_examples.mjs
    # or: node tests/emulator/run_examples.mjs --update-goldens

    git diff tests/emulator/goldens/   # review the change
    git add tests/emulator/goldens/
    git commit                          # explain WHY in the message

When a run fails without `UPDATE_GOLDENS`, the runner writes:

    tests/emulator/actual/<name>.png       the run's raw output
    tests/emulator/actual/<name>.diff.png  red-highlighted pixel diff

so reviewers can eyeball what changed without rerunning locally.
`actual/` is gitignored and re-created on every run. The CI job
now uploads `actual/`, `goldens/`, and `report.json` together as
a single `emulator-diff` artifact on failure — side by side means
the "what changed" story is obvious without cloning.

Implementation:

- `tests/emulator/screenshots/` is renamed to `tests/emulator/goldens/`.
  All 18 existing PNGs are preserved as the initial goldens (git
  detected them as pure renames).

- `harness.html` gets a new `window.nesHarness.rawPixelsBase64()`
  that returns the 245760-byte (256 × 240 × 4 bytes) RGBA canvas
  buffer as base64. The runner compares raw pixels, not PNG
  bytes, so encoder quirks (zlib level, filter heuristics) can't
  cause false positives across Chrome versions or platforms.

- The runner uses `pngjs` (pure-JS, no native deps) to decode
  goldens and to write diff PNGs. `PNG.sync.write` is
  byte-deterministic for identical pixels, so `git diff` on a
  committed golden only ever shows up when the actual rendered
  pixels changed — not because two machines produced slightly
  different compression.

- The committed goldens were re-encoded with pngjs in this commit
  so the baseline is consistent from day one. File sizes are a
  touch larger than Chrome's output (~1KB vs ~800B on average),
  but that's negligible and it eliminates one entire class of
  flaky-looking diffs in the future.

Determinism verification: I ran each of the 18 ROMs twice
through fresh `NES` instances in fresh puppeteer pages, hashed
the 245760-byte framebuffers at frame 180 with SHA-256, and
confirmed `run1 == run2` for every single one. Exact-pixel diffs
are safe for this ROM set.

Negative path verification: I corrupted one golden (flipped one
pixel to pure red via pngjs) and reran the runner. It printed

    DIFF  hello_sprite  1/61440 pixels differ; first at (120,120)
                        expected [255,0,0] got [0,0,0]
            actual: tests/emulator/actual/hello_sprite.png
              diff: tests/emulator/actual/hello_sprite.diff.png

and exited 1 as expected. The diff PNG shows a dim-grayscale
silhouette of the expected frame with a bright-red dot on the
one mismatched pixel — enough visual context to locate the
regression at a glance.

All 18 examples match their goldens in strict mode. `cargo fmt
--check`, `cargo clippy --release --all-targets -- -D warnings`,
and `cargo test --release` (313 unit + 37 integration) are all
still green.

https://claude.ai/code/session_014Z5y3Q9krLcAxYpZQJhZ5V
2026-04-12 21:30:18 +00:00