2D Buddy Sandbox

Minimal Rapier2D + Macroquad playground for prototyping RL-friendly simulations. The SimulationWorld struct seeds a simple scene (floor plus a falling rectangle) that can be reused offline or visualized in real time.

Prerequisites

• Rust toolchain stable (1.91 or newer recommended)
• macOS/Linux with GPU support for Macroquad (works headless/offline too)

Offline stepping (no graphics)

cargo run --release -- <steps>

• steps defaults to 240 when omitted.
• Prints sampled position/velocity data to stdout for logging into RL buffers.

Online visualization (Macroquad window)

cargo run --release --bin visualize [-- <step_limit>]

• Omit step_limit for an endless run.
• The renderer advances physics every few frames (FRAMES_PER_STEP) so you can tweak visuals without affecting the simulation state.

Saving physics states from the visualizer

While the visualizer is running you can press:

• D to dump the current physics state.

Each dump creates a directory under state_store/ (or the --state-dir you passed) with:

• state.bin – bincode-serialized SimulationWorld
• state.png – PNG screenshot of the current visual world

Example layout:

state_store/
  state_0123abcddeadbeef/
    state.bin
    state.png

GA training with saved states

The GA trainer (train_ga) will automatically use snapshots from state_store/ if they exist.

• Basic training run:

  cargo run --release --bin train_ga -- \
    --population 64 \
    --top-k 8 \
    --generations 50 \
    --output best_brain_stand_upright.bin

• During evaluation, each episode samples one snapshot from state_store/ (preferring state.bin files inside snapshot directories). If no states exist, it falls back to SimulationWorld::new().

When a new best brain is found, train_ga writes:

• best_brain_stand_upright.bin – network weights
• best_brain_stand_upright.bin.snapshots.txt – metadata describing which snapshot was used for that best evaluation:

best_score      <score>
snapshot_index  <index_into_loaded_snapshot_list>
snapshot_path   <path/to/state_store/.../state.bin>

Notes

• All scene constants live in src/lib.rs; tweak sizes, gravity, or damping there to explore new setups.
• The visualizer and offline runner both instantiate SimulationWorld::new() when no state is provided, ensuring trajectories match bit-for-bit between modes.