FS.GG.Game.Core 0.3.0

FS.GG.Game.Core

BCL-only deterministic simulation core for FS.GG.Game — the platform's bottom layer. Depends on nothing but FSharp.Core and reaches up to no other FS-GG package.

The sim vocabulary

The shared types — Point, Rect, Circle, ConvexPolygon, and the two detection values Contact (a penetration manifold) and RayHit (a segment-cast result) — live directly in the FS.GG.Game.Core namespace, so open FS.GG.Game.Core is all a caller needs. The tile index Cell is namespace-level too. Everything below is a [<RequireQualifiedAccess>] module, called as Grids.cellAt, Rng.nextInt, and so on.

• Rng — SplitMix64 seeded RNG (ofSeed/nextInt/nextFloat/nextBool/split), byte-identical across runs.
• FixedStep — fixed-timestep accumulator drain (drain/drainWith). No wall-clock read, so a scripted frame time replays exactly.

Collision — detection, then response

• Geometry — the detection surface: overlap and containment for AABB, circle, and convex polygon (intersects/contains/aabbContact/circleContact/polygonContact/obbPolygon), swept tests (sweptIntersects), and segment casts (segmentAabbHit/segmentCircleHit/segmentPolygonHit/…). It returns manifests as values and never resolves them.
• Resolution — the response layer that consumes a detection Contact and produces transforms (pushOut/slide/knockback). Deliberately separate from detection; it never re-detects.
• SpatialGrid — uniform spatial partitioning for the broad phase (build/query/queryRadius).

The grid

• Pathfinding — grid A*/BFS over walkable cells (astar/bfs), plus the many-to-one AI substrate distanceField/flowField/reachableWithin.
• Grids — the parts of a square grid: Edge, Vertex, GridSpec, the six adjacency conversions, and the pixel↔cell map (cellRect/cellCenter/edgeSegment/cellAt). Names the boundary between two tiles, which is where a wall lives.

Sight

• Los — point-to-point grid line of sight over a caller-supplied opacity predicate (line/supercover/trace/lineOfSight).
• Fov — grid field of view by symmetric shadowcasting (fov). Opacity is not walkability: this module consults opacity only.
• Visibility — the continuous-space sibling: exact point-to-point sight against arbitrary occluder segments, and the full angular-sweep visibility polygon (raySegment/isVisible/polygon). It can answer occlusion between two moving bodies, which a tile walk cannot.

Pathfinding, Los, and Fov all take terrain as a pure Cell -> bool predicate — the framework holds no map, so one terrain plugs into all three.

Where it came from

Three provenances:

• Extracted from FS.GG.UI.Canvas / FS.GG.UI.Scene and reimplemented BCL-only, per ADR-0022 — the shared types, Geometry, Rng, FixedStep, Pathfinding, SpatialGrid.
• Promoted from the frozen starter fragments in FS.GG.Rendering (template/fragments/*), which every game that wanted them previously had to copy and diverge from — Los, Visibility, Grids.
• Authored here through the SDD lifecycle, because the org had nothing to promote — Fov, Resolution.

Guarantees

Headlessly testable — zero Skia, zero Scene. Purity, totality (degenerate and non-finite input degrades to a documented value rather than throwing), and determinism (integer logic / float presentation) are the contract each module's .fsi states and its tests hold it to — so identical input yields byte-identical output across runs and platforms, and a module is safe to call from a replayed simulation step.

To project sim state onto drawables, add FS.GG.Game.Render.

House style: .fsi is the sole public surface; net10.0; -preview channel. See FS-GG/FS.GG.Game and ADR-0022.