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nescript/examples/platformer.ne

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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
// Platformer — an end-to-end side-scrolling demo game that
// exercises nearly every subsystem of the NEScript compiler in
// one program: custom CHR tiles, a full 32×30 background nametable
// with per-region attribute palettes, a multi-tile metasprite
// player with gravity/jump physics, wrap-around horizontal
// scrolling, moving enemies, collectible coins, a user-declared
// SFX envelope, a user-declared music track, and a title →
// playing → game-over state machine driven by both controller
// input and an autopilot so the jsnes golden harness (which runs
// headless with no simulated buttons) still captures an
// interesting frame-180 composition.
//
// Controls (when played by a human):
// D-pad left/right — walk
// A — jump
// Start — on title screen: begin; after game over: retry
//
// Build: cargo run --release -- build examples/platformer.ne
// Output: examples/platformer.nes
//
// All CHR tile art, nametable bytes, and attribute bytes in this
// file are generated by `cargo run --bin gen_platformer_tiles`.
// Regenerate them from `scripts/gen_platformer_tiles.rs` if you
// want to tweak the level.
game "Platformer" {
mapper: NROM
// Horizontal arrangement means nametable 1 mirrors nametable 0
// horizontally, so our single loaded nametable tiles endlessly
// as the camera scrolls right.
mirroring: horizontal
}
// ── Palette ──────────────────────────────────────────────────
// The background palette drives the sky / hill / ground look.
// Each sub-palette reserves index 0 for the shared background
// colour (sky blue $22), plus three working colours.
// bg 0 (sky region): sky blue, white, light gray, black
// bg 1 (air/blocks row): sky blue, red, peach, dark red
// bg 2 (ground row): sky blue, lime green, dark green, dark brown
// bg 3 (unused reserve): sky blue, yellow, orange, gold
// The sprite sub-palette 0 (used by every `draw` statement — the
// OAM attribute byte is always 0 in the current NEScript
// runtime) carries the hero's red/peach/white body colours.
// NOTE: the first byte of every sub-palette must match. The PPU
// mirrors $3F10/$3F14/$3F18/$3F1C onto $3F00/$3F04/$3F08/$3F0C, so
// writing 8 distinct "index 0" bytes ends up clobbering the
// background universal colour with the last write. The canonical
// fix — and what every NES game does — is to use the universal
// background colour ($22 sky blue here) in all 8 slots. For sprite
// palettes, index 0 is always transparent regardless of the stored
// value, so this costs nothing visually.
palette Main {
colors: [
// bg palette 0 — sky / clouds
// 0 = sky blue (universal bg)
// 1 = white
// 2 = light gray
// 3 = black
0x22, 0x30, 0x10, 0x0F,
// bg palette 1 — bricks, Q-blocks
// 1 = red, 2 = peach, 3 = dark red
0x22, 0x16, 0x27, 0x06,
// bg palette 2 — grass, hills, bushes, dirt
// 1 = light green
// 2 = light brown
// 3 = dark brown
0x22, 0x1A, 0x17, 0x07,
// bg palette 3 — unused but the mirroring still writes here
0x22, 0x28, 0x27, 0x17,
// sprite palette 0 — hero / enemy / coin
// (OAM attribute is always 0 in the current runtime so
// every sprite uses this one sub-palette)
// 1 = red cap, 2 = peach skin, 3 = white
0x22, 0x16, 0x27, 0x30,
// sprite palette 1 — reserved
0x22, 0x07, 0x17, 0x27,
// sprite palette 2 — reserved
0x22, 0x2A, 0x1A, 0x30,
// sprite palette 3 — reserved
0x22, 0x28, 0x18, 0x38
]
}
// ── Tileset ──────────────────────────────────────────────────
// One big sprite declaration holds every custom CHR tile used by
// both sprites and the background nametable. `draw Tileset ...
// frame: N` overrides the OAM tile-index byte with `N`, so the
// same declaration drives the player, enemies, coins, and every
// background tile after tile 0. Tile 0 is reserved by the linker
// for the built-in smiley — the background leaves it unreferenced.
sprite Tileset {
chr: [
// tile 1: Player head L
0x3F, 0x7F, 0x70, 0x61, 0xCF, 0xCD, 0xC0, 0xC0, 0x00, 0x00, 0x0F, 0x1F, 0x3F, 0x3F, 0x3F, 0x3F,
// tile 2: Player head R
0xFC, 0xFE, 0x0E, 0x83, 0xF8, 0x4C, 0x00, 0x00, 0x00, 0x00, 0xF0, 0xFC, 0xFF, 0xFF, 0xFF, 0xFF,
// tile 3: Player body L
0x7F, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0xE0, 0x00, 0x10, 0x18, 0x00, 0x7F, 0x7F, 0x67, 0x07,
// tile 4: Player body R
0xFE, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x07, 0x00, 0x08, 0x18, 0x00, 0xFE, 0xFE, 0xE6, 0xE0,
// tile 5: Enemy
0x3C, 0x7E, 0x76, 0xFF, 0x99, 0x7E, 0xBD, 0x99, 0x00, 0x00, 0x18, 0x38, 0x7E, 0x00, 0x00, 0x00,
// tile 6: Coin
0x00, 0x00, 0x18, 0x24, 0x24, 0x18, 0x00, 0x00, 0x18, 0x3C, 0x7E, 0x7E, 0x7E, 0x7E, 0x3C, 0x18,
// tile 7: Grass top
0xFF, 0xBB, 0xFF, 0xFF, 0xFF, 0xFF, 0xBD, 0xFF, 0x00, 0x00, 0x00, 0x6A, 0xF7, 0xFF, 0xFF, 0xFF,
// tile 8: Dirt
0xFF, 0xBD, 0xFF, 0xF7, 0xFF, 0xBD, 0xF7, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
// tile 9: Brick
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x82, 0x82, 0x82, 0xFF, 0x10, 0x10, 0x10,
// tile 10: Cloud L
0x00, 0x1C, 0x3E, 0x7F, 0x7F, 0x1F, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x60, 0x3E, 0x07,
// tile 11: Cloud R
0x00, 0x70, 0xF8, 0xFE, 0xFE, 0xF8, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x06, 0x7C, 0xE0,
// tile 12: Hill
0x00, 0x0C, 0x1E, 0x3F, 0x2F, 0x4B, 0x75, 0xC9, 0x00, 0x00, 0x00, 0x00, 0x10, 0x34, 0x0A, 0x36,
// tile 13: Bush
0x00, 0x18, 0x3C, 0x7E, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x02, 0x02, 0x06, 0x06, 0x55,
// tile 14: Q Block
0xFF, 0xFF, 0xC3, 0xDB, 0xD3, 0xC3, 0xFF, 0xFF, 0xFF, 0x81, 0xBD, 0xBD, 0xBD, 0xBD, 0x81, 0xFF,
// tile 15: Sky (blank)
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
]
}
// Tile index constants — must match `scripts/gen_platformer_tiles.rs`.
const TILE_PLAYER_HL: u8 = 1
const TILE_PLAYER_HR: u8 = 2
const TILE_PLAYER_BL: u8 = 3
const TILE_PLAYER_BR: u8 = 4
const TILE_ENEMY: u8 = 5
const TILE_COIN: u8 = 6
// ── Background ──────────────────────────────────────────────
// Full-screen 32×30 nametable showing a static level view that
// horizontal scrolling pans across. The attribute table splits
// the screen into three palette regions (sky/blocks/ground) so
// the grass and hills pick up the right colours even without
// per-tile attribute churn.
background Level {
tiles: [
// rows 0-4: clean sky
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
// row 5: clouds at x=4..5 and x=20..21
15, 15, 15, 15, 10, 11, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 10, 11, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
// row 6: cloud at x=12..13
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 10, 11, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
// rows 7-14: more clean sky
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
// row 15: brick/Q-block platform left, brick platform right
15, 15, 15, 15, 15, 15, 9, 9, 14, 9, 15, 15, 15, 15, 15, 15,
15, 15, 9, 9, 9, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
// rows 16-19: sky
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
// row 20: hills (3 on left, 4 on right)
15, 15, 12, 12, 12, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
15, 15, 15, 15, 15, 15, 12, 12, 12, 12, 15, 15, 15, 15, 15, 15,
// row 21: bushes above the grass line
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 13, 13, 13, 15, 15, 15,
15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 13, 13, 15, 15, 15,
// row 22: grass top (full width)
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
// rows 23-29: dirt with a few buried bricks for texture
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 8,
8, 8, 8, 8, 8, 9, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 9, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 9, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8
]
attributes: [
// 8×8 attribute grid, one byte per 32×32-px metatile group.
// Each byte packs 4 identical 2-bit quadrants selecting a
// sub-palette (0..3):
// 0x00 = sub-palette 0 (sky / clouds)
// 0x55 = sub-palette 1 (bricks / Q-blocks)
// 0xAA = sub-palette 2 (grass / hills / dirt)
//
// Row mapping: ay 0-2 (nt rows 0-11) = sky, ay 3 (nt rows
// 12-15) = brick row, ay 4 (nt rows 16-19) = more sky, ay
// 5-7 (nt rows 20-29) = ground.
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA,
0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA,
0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA
]
}
// ── Audio ────────────────────────────────────────────────────
// Custom boingy jump sound — descending pitch arc on pulse 1.
sfx Boing {
duty: 2
pitch: [0x30, 0x38, 0x40, 0x48, 0x50, 0x58, 0x60]
volume: [12, 11, 10, 9, 7, 5, 2]
}
// Custom coin ding — short rising blip.
sfx Ding {
duty: 2
pitch: [0x20, 0x20, 0x20, 0x20]
volume: [14, 12, 8, 3]
}
// Custom looping underworld theme — playful four-bar loop on
// pulse 2 that plays while the player is alive.
music Theme {
duty: 2
volume: 9
repeat: true
notes: [
37, 10, // C4
41, 10, // E4
44, 10, // G4
49, 10, // C5
44, 10, // G4
41, 10, // E4
39, 15, // D4
0, 5, // rest
36, 10, // B3
41, 10, // E4
44, 10, // G4
49, 20, // C5
0, 10 // rest
]
}
// ── Gameplay constants ──────────────────────────────────────
const PLAYER_SCREEN_X: u8 = 80 // fixed camera-relative X
const GROUND_Y: u8 = 160 // feet land here (y of head)
const JUMP_RISE: u8 = 12 // upward frames after take-off
const JUMP_PX: u8 = 3 // px moved each rise frame
const GRAVITY_CAP: u8 = 4 // terminal fall speed
const ENEMY_Y: u8 = 168 // enemies walk on the grass
const COIN_Y: u8 = 144 // coins float a bit above
// World-space X positions of the moving entities. Wrap-around
// arithmetic (u8) makes the level feel like an endless loop.
const ENEMY1_WORLD_X: u8 = 100
const ENEMY2_WORLD_X: u8 = 200
const COIN1_WORLD_X: u8 = 50
const COIN2_WORLD_X: u8 = 150
// ── Game state ──────────────────────────────────────────────
// Player physics
var player_y: u8 = 160
var on_ground: u8 = 1
var rise_count: u8 = 0 // frames of upward motion remaining
var fall_vy: u8 = 0 // gravity accumulator
// World/camera
var camera_x: u8 = 0
var frame_tick: u8 = 0 // free-running frame counter
var jump_timer: u8 = 0 // autopilot: jump every N frames
var anim_tick: u8 = 0 // visual animation phase
// ── Helper functions ────────────────────────────────────────
// Try to start a jump. Only valid when the player is on the
// ground (on_ground == 1); otherwise this is a no-op.
fun try_jump() {
if on_ground == 1 {
rise_count = JUMP_RISE
on_ground = 0
fall_vy = 0
play Boing
}
}
// Advance player physics one frame. Handles the jump-rise phase
// (upward movement while rise_count > 0) and the gravity fall
// phase (increment fall_vy each frame up to GRAVITY_CAP, clamp to
// GROUND_Y on landing).
fun step_physics() {
if rise_count > 0 {
// Clamp underflow so a too-high jump doesn't wrap into the
// bottom of the screen on an 8-bit subtraction.
if player_y >= JUMP_PX {
player_y -= JUMP_PX
} else {
player_y = 0
}
rise_count -= 1
} else {
player_y += fall_vy
if fall_vy < GRAVITY_CAP {
fall_vy += 1
}
if player_y >= GROUND_Y {
player_y = GROUND_Y
on_ground = 1
fall_vy = 0
}
}
}
// Draw the 2×2 hero metasprite at (PLAYER_SCREEN_X, player_y).
// Each `draw` statement writes a fresh OAM slot via the runtime
// cursor, so four calls produce four sprites occupying a 16×16
// block.
fun draw_player() {
draw Tileset at: (PLAYER_SCREEN_X, player_y ) frame: TILE_PLAYER_HL
draw Tileset at: (PLAYER_SCREEN_X + 8, player_y ) frame: TILE_PLAYER_HR
draw Tileset at: (PLAYER_SCREEN_X, player_y + 8) frame: TILE_PLAYER_BL
draw Tileset at: (PLAYER_SCREEN_X + 8, player_y + 8) frame: TILE_PLAYER_BR
}
// ── States ──────────────────────────────────────────────────
state Title {
var blink: u8 = 0
on enter {
blink = 0
frame_tick = 0
start_music Theme
}
on frame {
frame_tick += 1
blink += 1
if blink >= 60 {
blink = 0
}
// Blink a "press start" marker at roughly 0.5 Hz. We use
// the coin tile for visual continuity with the game world.
if blink < 30 {
draw Tileset at: (120, 120) frame: TILE_COIN
}
// Auto-advance so the jsnes golden harness (which never
// presses start) still reaches Playing and captures gameplay
// at frame 180. A human player can also press Start to skip
// the wait early.
if frame_tick >= 20 {
transition Playing
}
if button.start {
transition Playing
}
}
}
state Playing {
on enter {
player_y = GROUND_Y
on_ground = 1
rise_count = 0
fall_vy = 0
camera_x = 0
frame_tick = 0
jump_timer = 0
anim_tick = 0
}
on frame {
frame_tick += 1
anim_tick += 1
// ── Input ─────────────────────────────────────────────
// Human controls — these work even while the autopilot
// is running so you can stomp the demo at any time.
if button.a {
try_jump()
}
if button.right {
camera_x += 1 // walk forward by scrolling right
}
if button.left {
// Walk back (wraps the camera — the level is cyclic).
camera_x -= 1
}
// ── Autopilot ────────────────────────────────────────
// The headless golden harness never presses buttons, so
// we advance the camera and periodically hop all by
// ourselves. A human holding right still accelerates
// forward — the two effects compose.
camera_x += 1
jump_timer += 1
if jump_timer >= 40 {
jump_timer = 0
try_jump()
}
// ── Physics ──────────────────────────────────────────
step_physics()
// ── Collisions ───────────────────────────────────────
// Coin pickup when the player's screen X is within ±8 of
// a coin's screen position and the coin's Y range overlaps
// the player. Uses u8 subtraction so "screen X" of a
// world entity is just (world_x - camera_x).
var e1_sx: u8 = ENEMY1_WORLD_X - camera_x
var e2_sx: u8 = ENEMY2_WORLD_X - camera_x
var c1_sx: u8 = COIN1_WORLD_X - camera_x
var c2_sx: u8 = COIN2_WORLD_X - camera_x
// Coin collect: player occupies [80..96). A coin is "hit"
// when its screen X is in [72..96) (8-px tolerance on each
// side of the player's left edge).
if c1_sx >= 72 and c1_sx < 96 {
if player_y <= COIN_Y + 16 {
play Ding
}
}
if c2_sx >= 72 and c2_sx < 96 {
if player_y <= COIN_Y + 16 {
play Ding
}
}
// Enemy stomp: if we're above an enemy horizontally *and*
// we're mid-fall (fall_vy > 0), count the stomp and
// bounce. Otherwise just ignore — the enemy slides past.
if e1_sx >= 72 and e1_sx < 96 {
if fall_vy > 0 {
if player_y + 16 >= ENEMY_Y {
play hit
rise_count = 6
fall_vy = 0
}
}
}
// ── Drawing ──────────────────────────────────────────
draw_player()
// Enemies — walking on the grass line. anim_tick drives
// a small vertical bob so they visibly move on the golden.
var ey: u8 = ENEMY_Y
if (anim_tick & 16) != 0 {
ey = ENEMY_Y - 2
}
draw Tileset at: (e1_sx, ey) frame: TILE_ENEMY
draw Tileset at: (e2_sx, ENEMY_Y) frame: TILE_ENEMY
// Coins — alternate two vertical positions to fake a
// spin via position change (OAM attr flip isn't wired up
// in the current runtime).
var cy: u8 = COIN_Y
if (anim_tick & 8) != 0 {
cy = COIN_Y - 1
}
draw Tileset at: (c1_sx, cy) frame: TILE_COIN
draw Tileset at: (c2_sx, COIN_Y) frame: TILE_COIN
// ── PPU scroll latch ─────────────────────────────────
// Write the scroll at the very end of the frame so it's
// the last $2005 pair before the implicit wait_frame /
// NMI handshake, minimizing mid-frame artifacts.
scroll(camera_x, 0)
}
}
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