reikhelm/.dev/2026-05-28-procgen-map-core/tasks/03-grid.md

Task 3: Grid

Depends on: Task 1, Task 2

Context Files

• .dev/2026-05-28-procgen-map-core/spec/design.md — §4.2 (Grid).
• reikhelm-core/src/geometry.rs — Point, Rect (indexing + region iteration).
• reikhelm-core/src/lib.rs — append the module declaration here.

Files

• Create: reikhelm-core/src/grid.rs — generic Grid<T>.
• Modify: reikhelm-core/src/lib.rs — append pub mod grid;.

What to Build

A generic, bounds-safe 2D grid (spec §4.2) backed by a flat Vec<T> in row-major order. Generic on purpose: it's the map (Grid<Tile>) and also scratch buffers (Grid<u32>, Grid<f32>) during generation. All access is bounds-checked — out-of-bounds reads return None, out-of-bounds writes are no-ops (never panic). Neighbor queries return only in-bounds points. Derive Clone, Debug; derive Serialize, Deserialize gated on T: Serialize/Deserialize.

Interface Dependencies

• Consumes: Point, Rect from Task 2.
• Produces: Grid<T> with:
  • new(width: u32, height: u32, fill: T) -> Self where T: Clone
  • from_fn(width, height, f: impl Fn(Point) -> T) -> Self
  • width() -> u32, height() -> u32
  • in_bounds(Point) -> bool
  • get(Point) -> Option<&T>, get_mut(Point) -> Option<&mut T>, set(Point, T) (no-op if OOB)
  • neighbors4(Point) -> impl Iterator<Item = Point>, neighbors8(...) — in-bounds only
  • iter() -> impl Iterator<Item = (Point, &T)>
  • iter_rect(Rect) -> impl Iterator<Item = (Point, &T)> (clipped to bounds)

Tests

• get/set round-trip for in-bounds points; set OOB is a no-op and get OOB is None.
• neighbors4/neighbors8 at a corner return only in-bounds neighbors (3 for corner with 8-conn).
• iter visits exactly width * height cells once each.
• iter_rect is clipped when the rect extends past the grid edge.
• from_fn produces values matching the closure at sampled points.

Success Criteria

• Grid<T> exists with all listed methods; OOB access never panics.
• pub mod grid; added to lib.rs.
• All tests pass: cargo test -p reikhelm-core grid

Commit

"feat(core): generic bounds-safe Grid<T>"