mirror of
https://github.com/imjasonh/nescript
synced 2026-07-08 00:45:38 +00:00
82b3d0d20a
Closes §H. 2×2 metatiles and a parallel collision map are now a
first-class construct. `metatileset Name { metatiles: [{ id, tiles,
collide }, ...] }` declares a library of 2×2 tile bundles. `room Name
{ metatileset: M, layout: [...] }` lays them out on a 16×15 grid. The
compiler expands each room at compile time into:
- a 960-byte nametable (`__room_tiles_<name>`)
- a 64-byte attribute table (`__room_attrs_<name>`)
- a 240-byte collision bitmap (`__room_col_<name>`)
`paint_room Name` reuses the vblank-safe `load_background` update
machinery for the nametable blit and installs the collision bitmap
pointer into `ZP_ROOM_COL_LO`/`ZP_ROOM_COL_HI` (ZP $18/$19).
`collides_at(x, y)` JSRs into a small runtime helper that reads
`(room_col),Y` with `Y = (y & 0xF0) | (x >> 4)` and returns 0/1.
The helper links in only when the `__collides_at_used` marker is
emitted, so programs that declare a room but never query it pay
zero bytes for the subroutine.
`parse_byte_array` grows a `[value; count]` shortcut — 240-entry
`layout` arrays are unwieldy to spell out a byte at a time.
See `examples/metatiles_demo.ne` for the end-to-end flow: a probe
sprite bounces off walls via `collides_at` and lands on the left
side of the playfield at frame 180 — direct evidence that the
collision query works.
Also defers the register-allocator work from §"Code quality /
tooling" and documents the audio-goldens constraint in future-work
so the next agent sees it.
138 lines
5 KiB
Text
138 lines
5 KiB
Text
// Metatiles + collision demo — shows the `metatileset` /
|
||
// `room` declarations, `paint_room` at reset, and
|
||
// `collides_at(x, y)` as a runtime query that actually
|
||
// changes observable behaviour.
|
||
//
|
||
// What the program does:
|
||
//
|
||
// - Declares a `metatileset Blocks` with two 2×2 metatiles:
|
||
// `id 0` = floor (CHR tile 0 everywhere, non-colliding)
|
||
// `id 1` = wall (CHR tile 0 everywhere, colliding)
|
||
//
|
||
// Both metatiles use tile 0 in CHR (the built-in smiley) so
|
||
// we don't need a sprite declaration just to author tile
|
||
// data. The palette swap below is what visually distinguishes
|
||
// floor from wall.
|
||
//
|
||
// - Declares a `room Dungeon` whose 16×15 layout frames the
|
||
// playfield with wall metatiles and leaves the interior as
|
||
// floor. `paint_room Dungeon` at reset blits the expanded
|
||
// 32×30 nametable into NT 0 and installs the room's
|
||
// collision bitmap pointer so `collides_at` can answer
|
||
// queries against this room.
|
||
//
|
||
// - A probe sprite marches right along row 9 starting at x=120.
|
||
// Every frame the probe advances two pixels. Before drawing
|
||
// the sprite we query `collides_at(probe_x + 8, probe_y)` —
|
||
// the +8 puts the test point near the sprite's right edge.
|
||
// When the query returns true (we've hit the right wall)
|
||
// we flip `dx`, so the probe bounces back.
|
||
//
|
||
// With dx=2 and start x=120, the right-edge hit fires around
|
||
// frame 56 (probe_x reaches 232). The probe then bounces
|
||
// back at -2 per frame, so by frame 180 (the harness golden
|
||
// frame) it's well inside the playfield. A regression that
|
||
// silently returned 0 from `collides_at` would leave the
|
||
// probe stuck against the wall or wrapping the u8 x
|
||
// coordinate — either way, the committed golden wouldn't
|
||
// match.
|
||
//
|
||
// Build: cargo run --release -- build examples/metatiles_demo.ne
|
||
|
||
game "Metatiles Demo" {
|
||
mapper: NROM
|
||
}
|
||
|
||
metatileset Blocks {
|
||
metatiles: [
|
||
{ id: 0, tiles: [0, 0, 0, 0], collide: false },
|
||
{ id: 1, tiles: [0, 0, 0, 0], collide: true },
|
||
],
|
||
}
|
||
|
||
// 16×15 grid. `1` = wall (colliding), `0` = floor (free).
|
||
//
|
||
// ┌────────────────┐ row 0
|
||
// │wwwwwwwwwwwwwwww│ row 1-12 frame walls on the edges
|
||
// │w..............w│ and leave the interior as floor
|
||
// │w..............w│ tiles. Row 9 (the middle-ish)
|
||
// │w..............w│ is where the probe walks.
|
||
// │w..............w│
|
||
// │w..............w│
|
||
// │w..............w│
|
||
// │w..............w│
|
||
// │w..............w│
|
||
// │w..............w│
|
||
// │w..............w│
|
||
// │wwwwwwwwwwwwwwww│
|
||
room Dungeon {
|
||
metatileset: Blocks,
|
||
layout: [
|
||
// row 0 — top wall
|
||
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
|
||
// rows 1..13 — side walls bracket 14 floor cells
|
||
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
|
||
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
|
||
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
|
||
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
|
||
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
|
||
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
|
||
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
|
||
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
|
||
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
|
||
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
|
||
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
|
||
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
|
||
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
|
||
// row 14 — bottom wall
|
||
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
|
||
],
|
||
}
|
||
|
||
var probe_x: u8 = 120
|
||
var probe_y: u8 = 144 // roughly row 9 of the metatile grid
|
||
var dx: i8 = 2
|
||
var painted: u8 = 0
|
||
|
||
on frame {
|
||
// Paint the room once on the first frame. Doing this inside
|
||
// `on frame` (rather than an `on enter` handler) keeps the
|
||
// example minimal and avoids a separate state.
|
||
if painted == 0 {
|
||
paint_room Dungeon
|
||
painted = 1
|
||
}
|
||
|
||
// Move the probe two pixels per frame in whichever direction
|
||
// `dx` points. Two explicit branches because i8 runtime
|
||
// expressions don't compose directly with u8 assignment —
|
||
// keeping the sign logic out of the IR is cleaner than
|
||
// rigging up a cast chain.
|
||
if dx == 2 {
|
||
probe_x += 2
|
||
}
|
||
if dx == -2 {
|
||
probe_x -= 2
|
||
}
|
||
|
||
// Check the pixel just ahead of the probe's facing side.
|
||
// The probe is 8 pixels wide; testing at `probe_x + 8` is
|
||
// the right-edge probe and at `probe_x - 1` is the
|
||
// left-edge. Combined with the sprite width this means the
|
||
// probe flips direction one pixel before it would visually
|
||
// overlap the wall.
|
||
if dx == 2 {
|
||
if collides_at(probe_x + 8, probe_y) {
|
||
dx = -2
|
||
}
|
||
}
|
||
if dx == -2 {
|
||
if collides_at(probe_x - 1, probe_y) {
|
||
dx = 2
|
||
}
|
||
}
|
||
|
||
draw Probe at: (probe_x, probe_y)
|
||
}
|
||
|
||
start Main
|