What is box3d_demo?

This Godot 4.7 project is a demonstration of Box3D, a 3D physics engine created by Erin Catto (who also made the widely used Box2D). The engine is included as full source code, so you can build the physics libraries yourself on Windows or Linux and see how a C-based engine gets embedded into Godot. A fresh copy runs immediately on Windows because the prebuilt libraries are committed, so you can try it before building anything. The project extends the Godot binding for Box3D to expose nearly the entire engine API. From GDScript, you can create bodies, joints, and shapes, apply forces and impulses at specific points, change material properties on moving objects, cast rays, run overlap queries, and record a physics session for deterministic replay. The engine itself supports static, kinematic, and dynamic bodies, multiple collider types, continuous collision detection, and a multithreaded solver that produces identical results across platforms. On top of the engine, the demo builds several physics-driven systems. Structures fracture into irregular shards when struck, with debris finest at the impact point and coarser farther away, and pieces can break again on subsequent hits. Explosions deliver radial impulses that fracture everything in range, paired with visual effects like fireball shaders, shockwave rings, heat haze, camera shake, and slow motion. A fire simulation spreads deterministically between flammable objects based on distance, wind, and contact, with moisture boiling off before ignition and burning structures weakening until they collapse. Additional systems include glass panes that shatter from blast overpressure, impact, or thermal shock, producing shard patterns that crowd toward the break point. Water uses force-based buoyancy with drag so wood floats and dense objects sink, alongside a compute shader that generates interactive surface ripples. The scene also contains detailed structures like an industrial district with smokestacks and water towers, a tower crane with cable physics that sag and snap, a suspension bridge, and articulated human ragdolls. The full README is longer than what was shown.