sgl-core

Deterministic game building blocks with no I/O, clocks, threads, graphics, or dependencies on other SGL crates. The game supplies time, seeds, units, and state. Native clients, browser clients, and headless servers share the same API.

Choose a module

FixedClock::with_hz is render-paced: it clamps each frame delta to one fixed step and runs at most one simulation step per frame, so its cadence stays steady but simulation slows when frames are longer than a step. A simulation that must keep pace with elapsed time (an authoritative server or a networked client) uses FixedClock::with_catch_up instead: a CatchUp policy sets the most steps one frame runs and how many due steps carry to later frames (max_debt_steps: 0 discards everything past the frame's budget). begin_frame takes the frame's elapsed Duration and the clock accumulates it exactly in whole nanoseconds; fixed_step() is the exact step and fixed_dt() the same in f32 seconds. dropped_dt reports supplied time that will never be simulated. Use its interpolation fraction for presentation, keeping game simulation separate from rendering.

SplitMix64 and canonical hashes have frozen cross-target contracts. random::Rng is deterministic for a seed within its dependency version; its stream is not promised across dependency upgrades. Choose according to the game's replay or persistence requirements.

Collision units and the up axis belong to the game. Supply them through CollisionConfig; SGL does not choose a world scale or entity layout. collision is 2D arcade physics: it moves bodies the game drives, with no forces, mass or rotation. See Physics to choose a game's physics.

Read the core contract before changing deterministic behavior. Parity fixtures and property tests exercise the cross-target and algorithm boundaries.

Run cargo test -p sgl-core for focused native checks. The repository's required check also runs the WASM lane. For dependency setup, see Building games with SGL.