The status bar now paints into NT row 1 (coin + score digits on
the left, heart + lives digit on the right) using the `bg3`
sub-palette that matches `sp0` pixel-for-pixel. A single OAM
slot-0 anchor sprite sits over the coin tile; its one opaque
pixel lines up with the coin's bottom row so sprite-0 hit fires
at scanline 15, and a trailing `sprite_0_split(camera_x, 0)`
latches the playfield scroll starting at scanline 16. NT rows
0-1 stay pinned while scanlines 16+ scroll with the camera.
Score / lives updates are shadow-compared (`last_score`,
`last_lives`) so the VRAM ring sees an entry only when the
backing state actually changes — most frames append zero bytes.
OAM footprint drops from 5 sprites per frame down to 1.
Tile pipeline gains a 27th entry — a 7-transparent-row + 1-pixel
anchor — so the sprite-0 hit lands on scanline 15 instead of
scanline 8 (the latter would smear the HUD glyphs across the
split). `gen_platformer_tiles.rs` is updated in lockstep.
Ancillary changes: `bg3` retuned from `[yellow, orange,
dk_orange]` to `[red, orange, white]` (matching `sp0`);
`palette_map` row 0 flips from bg0 to bg3; legend gains `o`, `h`,
`0`, `3` so the initial map can preload the static HUD tiles and
the committed nametable already reads "coin 00 ... heart 3" on
frame 0.
`docs/future-work.md` loses the sprite-0 HUD follow-up section
(this commit lands it). Goldens + gif refreshed.
Root cause: `ZP_DIV_REMAINDER`, `ZP_MUL_RESULT_HI`, and
`ZP_CURRENT_STATE` all live at `$03`. The divide routine was
zeroing the byte on entry (`LDA #0; STA $03`) and writing the
running remainder there on every one of its 8 iterations; the
multiply routine accumulated its running product there. Any
multi-state program doing `u8 / 10` in `on_frame` had its state
ID clobbered on the way out of the routine — the next main-loop
dispatch read `$03 == 0` (or whatever the remainder happened to
be), matched state 0, and handed control to `Title` instead of
the current state. The platformer's HUD hit this once per blink
period: Playing survived exactly one frame, then Title took over
for 20 frames, then the cycle repeated.
Fix: rewrite both runtime routines to keep their running
accumulators in register A instead of `$03`. The new contracts:
- `__divide`: input `A = dividend`, `$02 = divisor`. Output
`A = remainder`, `$04 = quotient`. The algorithm shifts the
dividend-turning-into-quotient through `$04` (same as before)
and rotates the extracted bits into `A`, comparing and
subtracting directly without ever touching `$03`.
- `__multiply`: input `A = multiplicand`, `$02 = multiplier`.
Output `A = product` (low 8 bits — high byte discarded for
`u8 * u8 → u8` as before, but not via a `$03` write). The
multiplicand gets shifted left each iteration via `$04` and
the running sum stays in `A`.
`IrOp::Div` lowering gains one extra `LDA $04` after the JSR to
pick up the quotient; `IrOp::Mod` loses the old `LDA $03` since
the remainder is already in A. Net callsite cost is one
instruction either way.
Added two regression tests — `divide_routine_does_not_touch_zp_03`
and `multiply_routine_does_not_touch_zp_03` — that walk the
emitted instruction stream and fail loudly on any ZeroPage($03)
access, so a future refactor can't silently reintroduce the
alias.
Rebuilt the three ROMs that use `/` or `*` (bitwise_ops,
mmc1_banked, platformer) and re-baselined the platformer audio
golden — the new instruction count shifts vblank-relative audio
timing by a few cycles, as the CLAUDE.md audio-churn note warns.
Pixel goldens and docs/platformer.gif stay byte-identical. The
platformer HUD is back on native `stomp_count / 10` + `% 10`;
the subtraction-loop workaround is gone.
docs/future-work.md gains a new section describing the planned
sprite-0 hit upgrade for the platformer HUD (carry-over task
from the branch).
Upgrades the platformer's "live coin count" into a proper heads-up
display that stays pinned to the top of the viewport while the
nametable scrolls. Left side: coin icon + two-digit stomp tally.
Right side: red heart icon + single-digit lives counter. Both ride
through the GameOver screen without jumping position, so the death
banner reads as a continuation of the same run.
Wire-up: three new cross-state bits — score now accumulates across
lives, `lives` starts at 3 and decrements in `GameOver.on_enter`,
and the GameOver → Playing retry bounces to Title instead when the
last heart is spent (Title's `on_enter` refills both).
Tile pipeline: ten decimal digits + a heart glyph added to the
committed Tileset (generator source in `scripts/gen_platformer_tiles.rs`
kept in sync). Digits use `c` (white) so they read against the
sky; the heart uses `a` (red) to match the cap/brick palette.
Division workaround: the obvious `stomp_count / 10` / `% 10` pair
miscompiles near state transitions — the built ROM cycles
Title → Playing → Title once per blink period with Playing
surviving exactly one frame. Swapping both calls for repeated
`while r >= 10 { r -= 10 }` helpers fixes it. Documented as a
new entry in `docs/future-work.md` so the next person reaching
for `/` or `%` knows to check there first.
Goldens, docs/platformer.gif, and the top-level + examples README
entries all refreshed in the same commit.
Both examples declared their gameplay variables at the top level
even though every read and write happened inside one specific state.
That pattern hid the overlay feature from new users and kept the
state-local code path from being exercised outside the dedicated
`state_machine.ne` demo (which is how the "state-locals silently
drop their writes" bug survived so long).
`coin_cavern.ne`: the five Playing-only physics/position/inventory
vars (`player_x`, `player_y`, `player_vy`, `on_ground`,
`coins_left`) move onto Playing's state block. `score` stays
global because GameOver-era code could reasonably grow to read it.
The `on_enter` body loses its redundant resets — the declared
initializers on the state-locals re-run on every entry, so
retrying after `transition Title` comes back to a fresh state.
`platformer.ne`: player physics, camera, liveness, animation
phase, and the autopilot budget (`player_y`, `on_ground`,
`rise_count`, `fall_vy`, `camera_x`, `anim_tick`, `alive`,
`auto_jumps`) all move onto Playing. `frame_tick` and
`stomp_count` stay global — Title reads the former to
auto-advance, GameOver reads the latter to tally coins on the
death screen. The analyzer now overlays Title's `blink`,
Playing's eight physics vars, and GameOver's `linger` starting
at the same ZP byte (`$1A`), so the three scenes share a
9-byte window instead of each claiming their own slots.
Byte-level ROM bytes for both examples shift because variable
addresses moved. Video goldens stay pixel-identical (the harness
doesn't see Playing in coin_cavern, and the pre-transition
Title→Playing timing in platformer is preserved); the platformer
audio hash needed one more refresh because the now-slightly-shorter
reset prologue shifts APU writes within each frame.
https://claude.ai/code/session_015kvJu3iEFLSRJoShPBfm3X
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
Rewrites every example with non-trivial asset declarations to use
the pleasant QoL syntax introduced in the previous commit. Every
example still compiles to a byte-identical ROM (verified by a
temp-path diff before committing), so the committed `.nes` files
and the 23 emulator goldens are unchanged.
* platformer.ne — the centerpiece end-to-end demo:
- `palette Main` goes to grouped form with a shared
`universal: 0x22` (sky blue), one shared colour per
sub-palette, and named NES colours throughout; the
long-standing `$3F10` mirror-trap warning is now handled
by the parser and the manual pitfall comment is gone.
- `sprite Tileset` is 15 tiles of ASCII pixel art instead
of 240 bytes of inline hex.
- `background Level` uses a `legend { '.': 15, '#': 9, ... }`
block plus `map:` strings for the 32×30 nametable, and
`palette_map:` rows for the attribute table. The map
reads top-down like the rendered screen.
- SFX latch-once `pitch: 0x30` scalars + `envelope:` alias.
- `music Theme` uses note names + `tempo: 10` default.
* audio_demo.ne — scalar sfx pitches, `envelope:` alias, and a
note-name `C4, E4, G4, ...` music track.
* palette_and_background.ne — grouped CoolBlues / WarmReds
palettes with `universal: black` + named colours, plus
`legend` + `map:` tilemaps for the two backgrounds.
* sprites_and_palettes.ne — Arrow and Heart sprites rewritten
as `pixels:` ASCII art.
Along the way, two small parser extensions support the rewrites:
- `parse_pixel_art` now accepts `a/b/c` as aliases for `#/%/@`,
matching the vocabulary every NES editor (and our own
gen_platformer_tiles.rs generator) uses.
- `palette_map_to_attrs` allows up to 16 metatile rows (the
full attribute-table coverage, including the off-screen
bottom half) and auto-replicates row 14 → row 15 when only
15 rows are supplied so the visible bottom of the screen
gets consistent sub-palette assignments by default. The old
15-row cap couldn't match a hand-packed `0xAA` attribute
table for the last row; the platformer required this to
stay byte-identical.
`scripts/gen_platformer_tiles.rs` is updated to emit the new
syntax directly (pixel-art `pixels:` block + `legend`/`map:`/
`palette_map:` for the background), so regenerating the
platformer tiles stays a one-liner.
474 lib tests + 64 integration tests pass (3 new parser tests
for `palette_map:` 15/16/17 rows and the `abc` alias). All 23
emulator goldens still match pixel- and sample-for-sample.
https://claude.ai/code/session_01PzaSFj3VahDzxEYTKCESkz
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
