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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` /
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// `room` declarations, `paint_room` at reset, and
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// `collides_at(x, y)` as a runtime query that actually
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// changes observable behaviour.
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//
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// What the program does:
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//
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// - Declares a `metatileset Blocks` with two 2×2 metatiles:
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// `id 0` = floor (CHR tile 0 everywhere, non-colliding)
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// `id 1` = wall (CHR tile 0 everywhere, colliding)
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//
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// Both metatiles use tile 0 in CHR (the built-in smiley) so
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// we don't need a sprite declaration just to author tile
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// data. The palette swap below is what visually distinguishes
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// floor from wall.
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//
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// - Declares a `room Dungeon` whose 16×15 layout frames the
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// playfield with wall metatiles and leaves the interior as
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// floor. `paint_room Dungeon` at reset blits the expanded
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// 32×30 nametable into NT 0 and installs the room's
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// collision bitmap pointer so `collides_at` can answer
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// queries against this room.
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//
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// - A probe sprite marches right along row 9 starting at x=120.
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// Every frame the probe advances two pixels. Before drawing
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// the sprite we query `collides_at(probe_x + 8, probe_y)` —
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// the +8 puts the test point near the sprite's right edge.
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// When the query returns true (we've hit the right wall)
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// we flip `dx`, so the probe bounces back.
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//
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// With dx=2 and start x=120, the right-edge hit fires around
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// frame 56 (probe_x reaches 232). The probe then bounces
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// back at -2 per frame, so by frame 180 (the harness golden
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// frame) it's well inside the playfield. A regression that
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// silently returned 0 from `collides_at` would leave the
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// probe stuck against the wall or wrapping the u8 x
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// coordinate — either way, the committed golden wouldn't
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// match.
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//
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// Build: cargo run --release -- build examples/metatiles_demo.ne
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game "Metatiles Demo" {
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mapper: NROM
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}
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metatileset Blocks {
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metatiles: [
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{ id: 0, tiles: [0, 0, 0, 0], collide: false },
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{ id: 1, tiles: [0, 0, 0, 0], collide: true },
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],
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}
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// 16×15 grid. `1` = wall (colliding), `0` = floor (free).
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//
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// ┌────────────────┐ row 0
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// │wwwwwwwwwwwwwwww│ row 1-12 frame walls on the edges
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// │w..............w│ and leave the interior as floor
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// │w..............w│ tiles. Row 9 (the middle-ish)
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// │w..............w│ is where the probe walks.
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// │w..............w│
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// │w..............w│
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// │w..............w│
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// │w..............w│
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// │w..............w│
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// │w..............w│
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// │w..............w│
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// │wwwwwwwwwwwwwwww│
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room Dungeon {
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metatileset: Blocks,
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layout: [
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// row 0 — top wall
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1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
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// rows 1..13 — side walls bracket 14 floor cells
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
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1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
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// row 14 — bottom wall
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1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
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],
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}
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var probe_x: u8 = 120
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var probe_y: u8 = 144 // roughly row 9 of the metatile grid
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var dx: i8 = 2
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var painted: u8 = 0
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on frame {
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// Paint the room once on the first frame. Doing this inside
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// `on frame` (rather than an `on enter` handler) keeps the
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// example minimal and avoids a separate state.
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if painted == 0 {
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paint_room Dungeon
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painted = 1
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}
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// Move the probe two pixels per frame in whichever direction
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// `dx` points. Two explicit branches because i8 runtime
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// expressions don't compose directly with u8 assignment —
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// keeping the sign logic out of the IR is cleaner than
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// rigging up a cast chain.
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if dx == 2 {
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probe_x += 2
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}
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if dx == -2 {
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probe_x -= 2
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}
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// Check the pixel just ahead of the probe's facing side.
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// The probe is 8 pixels wide; testing at `probe_x + 8` is
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// the right-edge probe and at `probe_x - 1` is the
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// left-edge. Combined with the sprite width this means the
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// probe flips direction one pixel before it would visually
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// overlap the wall.
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if dx == 2 {
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if collides_at(probe_x + 8, probe_y) {
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dx = -2
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}
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}
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if dx == -2 {
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if collides_at(probe_x - 1, probe_y) {
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dx = 2
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}
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}
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draw Probe at: (probe_x, probe_y)
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}
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start Main
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