Fulcrum

Fulcrum is an opinionated 2D game engine for Rust: the hard parts abstracted away, a small prelude-driven API on top, and strong defaults so you spend your time making the game. It targets everything from arcade games to RTS and simulation titles — sprites only, no 3D — with ECS as a first-class pattern, data-driven content (animations, prefabs, UI) throughout, and modding as a first-class feature.

Locked architectural decisions

• ECS: bevy_ecs, fully wrapped behind Fulcrum's own prelude — games never import bevy_ecs directly.
• Platform/rendering: winit + wgpu, sprite-batch renderer, ECS-component-driven drawing (immediate mode exists only for debug gizmos).
• Determinism: same-binary determinism is a core promise — fixed-timestep simulation with render interpolation, tick-sampled input, seeded RNG. Same build + same inputs = same result (enables replays and same-platform lockstep). See docs/determinism.md.
• Audio: kira. Modding: layered asset VFS + Lua (mlua).
• Conventions: 1 world unit = 1 pixel, +Y up; simulation mutates state only in FixedUpdate.

Workspace layout

• crates/fulcrum — facade crate; use fulcrum::prelude::*; is the whole API.
• crates/fulcrum-core — app builder, plugins, schedules, time, input, RNG.
• crates/fulcrum-render — window, wgpu backend, sprite batching.
• crates/fulcrum-asset — asset handles, storage, loaders.
• games/ — milestone games that dogfood the engine (pong, then asteroids, dungeon, RTS slice).

Learning Fulcrum

Start with The Fulcrum Book — it teaches the whole engine by building a small game (games/grove) from an empty window up. Build the rendered version with mdbook build book (output in book/built/). Every chapter's complete program compiles in CI as an example: cargo run -p grove --example ch01_window. New to games entirely? The book's From Zero track builds Snake from first principles, code-along style.

Deep dives (books/) take one system each and cover it completely, tutorial first:

• Animation — clips, the Aseprite pipeline, state machines, and frame-keyed gameplay, building games/dojo along the way.

Status

Pre-alpha. Phases 1-3 complete (core, 2D essentials, data-driven layer); phase 4 (modding, particles, pathfinding, replays) is planned. Build plans live in plans/; the milestone games in games/ double as integration tests.