mirror of
https://github.com/imjasonh/nescript
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5e5bed39a5
W0109 (shipped last commit) catches the 8-sprites-per-scanline
hardware limit at compile time for static layouts, but the
dynamic case — enemy formations, projectile clusters, animated
NPCs where coordinates come from variables — was still silent.
This change adds two layers of defense on top of W0109:
Layer 2: `cycle_sprites` runtime flicker intrinsic
New keyword statement that rotates the OAM DMA start offset
one slot per call. When called once per `on frame`, the PPU's
sprite evaluation picks up a different subset of the 12+
overlapping sprites each frame, so the permanent-dropout
failure mode becomes visible flicker — the classic NES
technique used by Gradius, Battletoads, and every shmup.
Implementation:
- Lexer keyword `KwCycleSprites` and parser production.
- AST `Statement::CycleSprites(Span)`.
- `IrOp::CycleSprites` lowered by the IR pass.
- Codegen emits `LDA $07EF / CLC / ADC #4 / STA $07EF` with
natural u8 wrap, plus a one-shot `__sprite_cycle_used`
marker label the first time it fires.
- Linker detects the marker and switches `gen_nmi` to the
cycling variant, which reads the rotating offset from
`$07EF` into OAM_ADDR before the DMA instead of writing
a literal 0. Programs that don't call `cycle_sprites`
skip the marker and get byte-identical ROM output.
Layer 3: debug-mode sprite overflow telemetry
Mirrors the frame-overrun pair (`debug.frame_overrun_count` /
`debug.frame_overran`). In debug builds the NMI handler reads
`$2002` at the top of vblank, masks bit 5 (the PPU's sprite
overflow flag), and if set bumps a cumulative counter at
`$07FD` plus a sticky bit at `$07FC`. The sticky bit clears
on every `wait_frame`.
New debug builtins:
- `debug.sprite_overflow_count()` → u8 peek of $07FD
- `debug.sprite_overflow()` → u8 peek of $07FC (sticky bit)
The hardware flag has well-known quirks but is correct for
the overwhelming majority of cases and costs ~15 cycles per
frame to sample. Release builds emit no overflow-check code
at all, so the four bytes at `$07EF` / `$07FC`-`$07FD` stay
free for user allocation.
Related changes:
- `gen_nmi` now takes an `NmiOptions` struct. Four bool
parameters tripped clippy's `fn_params_excessive_bools`.
- CLI `build` now renders analyzer warnings on a successful
build. Previously warnings were silently dropped unless
the user also ran `nescript check`, which made W0109
effectively invisible to CI and local dev alike. Existing
pre-existing W0103 / W0106 warnings on `coin_cavern`,
`mmc3_per_state_split`, `sprites_and_palettes` surface
too — not regressions, just now visible.
New example: `examples/sprite_flicker_demo.ne`
Draws 12 sprites into a 4-pixel band, W0109 fires at compile
time with nine labels pointing at the offenders, and a
`cycle_sprites` call at the end of `on frame` turns the
hardware dropout into flicker. The committed emulator golden
captures one frame of the cycling pattern (deterministic).
Tests:
- `runtime::tests::nmi_debug_mode_samples_sprite_overflow`
- `runtime::tests::nmi_sprite_cycle_variant_reads_rotating_offset`
- `ir_codegen::*::debug_sprite_overflow_count_loads_07fd`
- `ir_codegen::*::debug_sprite_overflow_flag_loads_07fc`
- `ir_codegen::*::wait_frame_clears_sprite_overflow_sticky_in_debug_mode`
- `ir_codegen::*::wait_frame_release_does_not_touch_sprite_overflow_sticky`
- `ir_codegen::*::cycle_sprites_emits_marker_and_add4`
- `ir_codegen::*::cycle_sprites_marker_dedup_across_multiple_calls`
- `ir_codegen::*::program_without_cycle_sprites_emits_no_marker`
- `analyzer::*::accepts_debug_sprite_overflow_builtins`
- `analyzer::*::rejects_unknown_debug_method_lists_all_four_known_names`
- `analyzer::*::accepts_cycle_sprites_statement`
Docs: `examples/war/COMPILER_BUGS.md` §4 now describes all three
layers (W0109, `cycle_sprites`, debug telemetry) with reasoning
for when each applies. `README.md` and `examples/README.md` add
the new example to their tables.
All 32 emulator goldens still match — the cycling is opt-in
and programs that don't call `cycle_sprites` or enable debug
mode are byte-identical to the pre-change output.
https://claude.ai/code/session_0143dTgh3UeRrtfHgQwzcv5z
143 lines
9.2 KiB
Markdown
143 lines
9.2 KiB
Markdown
# NEScript
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A statically-typed, compiled programming language for NES game development.
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NEScript compiles `.ne` source files directly into playable iNES ROM files, with no external assembler or linker dependencies. The compiler handles everything from source text to a ROM you can run in any NES emulator.
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_Source: [`examples/platformer.ne`](examples/platformer.ne)_
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## Quick Start
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```bash
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# Build the compiler
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cargo build --release
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# Compile an example
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cargo run -- build examples/hello_sprite.ne
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# Run the output ROM in an emulator
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# (produces examples/hello_sprite.nes)
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```
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## Hello World
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```
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game "Hello" {
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mapper: NROM
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}
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var px: u8 = 128
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var py: u8 = 120
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on frame {
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if button.right { px += 2 }
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if button.left { px -= 2 }
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if button.down { py += 2 }
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if button.up { py -= 2 }
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draw Smiley at: (px, py)
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}
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start Main
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```
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## Features
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- **Game-aware syntax** -- states, sprites, palettes, backgrounds, and input are first-class constructs
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- **Full type system** -- `u8`, `i8`, `u16`, `bool`, fixed-size arrays (`u8[N]`), `enum`, `struct`
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- **Rich control flow** -- `if`/`else`, `while`, `for i in 0..N`, `loop`, `match`
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- **Functions** -- with parameters, return types, `inline` hint, recursion detection
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- **State machines** -- `state` with `on enter`, `on exit`, `on frame`, `on scanline(N)` handlers
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- **Compile-time safety** -- call depth limits, recursion detection, type checking, unused-var warnings
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- **IR-based optimizer** -- constant folding, dead code elimination, strength reduction (incl. div/mod by power-of-two), copy propagation, peephole passes including INC/DEC fold and live-range slot recycling
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- **Full 16-bit arithmetic** -- u16 add/sub/compare lower to carry-propagating paired operations
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- **Multiple mappers** -- NROM, MMC1, UxROM, MMC3 (including multi-scanline IRQ dispatch per state)
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- **Audio subsystem** -- frame-walking pulse driver with user-declared `sfx`/`music` blocks, builtin effects and tracks, period table, and zero-cost elision when unused
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- **Palette & background pipeline** -- `palette` and `background` blocks, initial values loaded at reset, vblank-safe `set_palette` / `load_background` runtime swaps
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- **Asset pipeline** -- PNG-to-CHR conversion, inline tile data, sfx envelopes, music note streams
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- **Inline assembly** -- `asm { ... }` with `{var}` substitution, plus `raw asm { ... }` for verbatim blocks
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- **Hardware intrinsics** -- `poke(addr, value)` / `peek(addr)` for direct register access
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- **Debug support** -- `--debug` flag enables `debug.log` / `debug.assert` writes to the emulator debug port
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- **Compile-time diagnostics** -- `--dump-ir`, `--memory-map`, `--call-graph` flags
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- **Single binary** -- no dependencies on ca65, Python, or any external tools
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## Documentation
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- **[Language Guide](docs/language-guide.md)** -- complete reference for every language feature
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- **[Architecture](docs/architecture.md)** -- compiler internals and module overview
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- **[NES Reference](docs/nes-reference.md)** -- hardware quick reference for contributors
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- **[Examples README](examples/README.md)** -- how to build and run examples
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## Examples
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| Example | Features demonstrated |
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|---------|---------------------|
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| [`hello_sprite.ne`](examples/hello_sprite.ne) | D-pad input, sprite drawing |
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| [`bouncing_ball.ne`](examples/bouncing_ball.ne) | Automatic movement, edge detection |
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| [`coin_cavern.ne`](examples/coin_cavern.ne) | Multi-state game, functions, constants, gravity |
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| [`arrays_and_functions.ne`](examples/arrays_and_functions.ne) | Arrays, functions, while loops, inline functions |
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| [`state_machine.ne`](examples/state_machine.ne) | State transitions, on enter/exit, timers |
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| [`sprites_and_palettes.ne`](examples/sprites_and_palettes.ne) | Inline CHR data, scroll, type casting |
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| [`mmc1_banked.ne`](examples/mmc1_banked.ne) | MMC1 mapper, bank declarations, multiply |
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| [`uxrom_user_banked.ne`](examples/uxrom_user_banked.ne) | UxROM mapper with a `bank Foo { fun ... }` block — first example to put real user code in a switchable bank, called via a generated cross-bank trampoline |
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| [`uxrom_banked_to_banked.ne`](examples/uxrom_banked_to_banked.ne) | UxROM with two `bank Foo { fun ... }` blocks — exercises a banked→banked call (`step` in `Logic` calls `clamp` in `Helpers`) routed through the same trampoline that handles fixed→banked |
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| [`palette_and_background.ne`](examples/palette_and_background.ne) | Palette and background declarations, reset-time load, vblank-safe `set_palette` / `load_background` swaps |
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| [`auto_chr_background.ne`](examples/auto_chr_background.ne) | `background Stage @nametable("file.png")` with **automatic CHR generation** — the resolver dedupes the PNG's 8×8 cells, encodes them as 2-bitplane CHR, and slots them into CHR ROM after the sprite tile range |
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| [`friendly_assets.ne`](examples/friendly_assets.ne) | **Pleasant asset syntax** — named NES colours, grouped `bg0..sp3` palettes with `universal:`, ASCII pixel-art sprites, `legend { } + map:` tilemaps, `palette_map:` attribute grids, scalar sfx `pitch:`, note-name music with `tempo:` |
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| [`structs_enums_for.ne`](examples/structs_enums_for.ne) | Structs, enums, `for` loops, struct literals |
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| [`nested_structs.ne`](examples/nested_structs.ne) | Nested-struct fields (`hero.pos.x`) and array struct fields (`hero.inv[0]`) with chained literal initializers |
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| [`inline_asm_demo.ne`](examples/inline_asm_demo.ne) | Inline asm with `{var}` substitution, `poke`/`peek` |
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| [`audio_demo.ne`](examples/audio_demo.ne) | Audio subsystem: user `sfx`/`music` blocks, builtin effects, `play`/`start_music`/`stop_music` |
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| [`noise_triangle_sfx.ne`](examples/noise_triangle_sfx.ne) | Noise and triangle channel sfx via `channel: noise` / `channel: triangle` on `sfx` blocks |
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| [`sfx_pitch_envelope.ne`](examples/sfx_pitch_envelope.ne) | Per-frame pulse `pitch:` arrays — the audio tick walks the pitch envelope in lockstep with the volume envelope and writes `$4002` on every NMI for a frequency-sweeping siren tone |
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| [`metasprite_demo.ne`](examples/metasprite_demo.ne) | `metasprite Hero { sprite: ..., dx: [...], dy: [...], frame: [...] }` declarative multi-tile groups — `draw Hero at: (x, y)` expands to one OAM slot per tile so 16×16 sprites stop needing four hand-written `draw` statements |
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| [`sprite_flicker_demo.ne`](examples/sprite_flicker_demo.ne) | `cycle_sprites` — rotates the OAM DMA start offset one slot per frame so scenes with more than 8 sprites on a scanline drop a *different* one each frame. Turns the NES's permanent sprite-dropout hardware symptom into visible flicker, which the eye reconstructs from adjacent frames. Pairs with the compile-time `W0109` warning and the debug-mode `debug.sprite_overflow()` / `debug.sprite_overflow_count()` telemetry for a three-layer defense against the 8-sprites-per-scanline limit. |
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| [`platformer.ne`](examples/platformer.ne) | **End-to-end side-scroller** — custom CHR tileset, full background nametable, metasprite player with gravity/jump physics, wrap-around scrolling, stomp-or-die enemy collisions, live stomp-count HUD, pickup coins, user-declared SFX + music, and a Title → Playing → GameOver state machine with a proximity-based autopilot so the headless harness demonstrates the full gameplay loop (stomp, stomp, die, retry) inside six seconds |
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| [`war.ne`](examples/war.ne) | **Production-quality card game** — a complete port of War split across `examples/war/*.ne`: title screen with a 0/1/2-player menu, animated deal, sliding face-up cards, deck-count HUD, "WAR!" tie-break with buried cards, victory screen with a fanfare, and a brisk 4/4 march on pulse 2. Pulls in nearly every NEScript subsystem (custom 88-tile sheet, felt nametable, 8-bit LFSR PRNG, queue-based decks, phase machine inside `Playing`, multiple sfx + music tracks). Building it surfaced five compiler bugs / limitations, all catalogued in [`examples/war/COMPILER_BUGS.md`](examples/war/COMPILER_BUGS.md) — two fixed in the same PR. |
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## Compiler Commands
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```bash
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# Compile to ROM
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nescript build game.ne
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# Compile with custom output path
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nescript build game.ne --output my_game.nes
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# Type-check only (no ROM output)
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nescript check game.ne
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# View generated 6502 assembly
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nescript build game.ne --asm-dump
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# Enable debug mode
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nescript build game.ne --debug
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```
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## Emulator Compatibility
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Output ROMs are standard iNES format and work with any NES emulator:
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- **[Mesen](https://www.mesen.ca/)** -- recommended, best debugging support
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- **[FCEUX](https://fceux.com/)**
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- **[Nestopia](http://nestopia.sourceforge.net/)**
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## Project Status
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NEScript implements all five planned milestones:
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| Milestone | Status | Key Features |
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|-----------|--------|-------------|
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| M1: Hello Sprite | Done | Full compiler pipeline, assembler, ROM builder |
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| M2: Game Loop | Done | Functions, arrays, IR, optimizer, call graph analysis |
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| M3: Asset Pipeline | Done | PNG-to-CHR, sprites, `debug.log` / `debug.assert` |
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| M4: Optimization | Done | Strength reduction, ZP promotion, type casting, asm-dump |
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| M5: Bank Switching | Done | MMC1/UxROM/MMC3, bank declarations, software mul/div |
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497 tests across the lexer, parser, analyzer, IR, optimizer, codegen, assembler, linker, runtime, ROM, and asset modules, with CI running fmt, clippy, test, and example compilation on every push.
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## License
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[MIT](LICENSE)
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