Collision
Collision callback payload for body-level listeners.
The engine reports a collision between two registered bodies. Bodies are identified by their registration keys from Modifier.physicsBody(key = ...).
Impulse and normal
impulse is a scalar collision impulse magnitude that has already been converted for UI-space scaling.
In the JVM backend it is produced by taking the Box2D impulse in physics units and converting it via dev.zinchenko.physicsbox.units.PhysicsUnits (PxPerMeter/worldScale).
Treat this as a px-scaled magnitude suitable for UX effects (sound/haptics/FX thresholds), not as raw physics units.
Treat as px-scaled magnitude (UI scale), not N·s and not m·kg/s.
(normalX, normalY) is the contact normal in world/container space as reported by the engine. In the current backend the normal points from this body toward the other body; conventions may differ across physics engines.
All numeric values are intended for UI feedback / effects (sound volume, haptics, particles) and should not be treated as strictly physically accurate across different engines or solver settings.
Parameters
Key of the body that owns the listener (the “this” body).
Key of the other body involved in the collision.
Contact impulse magnitude converted to UI px-scale via PhysicsUnits.
X component of the reported collision normal.
Y component of the reported collision normal.