Global Physics Config¶

The global.physics_config resource defines physics materials, collision filters, and actor classes used by Crown’s physics simulation. The file is stored in SJSON format and must be edited manually.

Example¶

materials = {
    default = { friction = 0.8 restitution = 0.81 }
}

collision_filters = {
    no_collision = { collides_with = [] }
    default = { collides_with_all_except = [ "no_collision" ] }
}

actors = {
    static = { dynamic = false }
    dynamic = { dynamic = true }
    keyframed = { dynamic = true kinematic = true disable_gravity = true }
    trigger = { trigger = true }
}

Materials¶

Physics materials define surface response parameters for actors. Create a new material by adding an entry to the materials object:

materials = {
    default = ...
    slippery = { friction = 0.1 }
}

Common material properties:

friction: general contact friction; larger values increase resistance to sliding.
rolling_friction: torsional friction orthogonal to the contact normal; helps stop spheres rolling forever.
spinning_friction: torsional friction around the contact normal; useful for grasping.
restitution: coefficient of restitution; 1 = perfectly elastic collision, < 1 = inelastic.

Collision filters¶

Collision filters control which actors interact with which. Define a filter by adding an entry to the collision_filters object:

collision_filters = {
    ...
    wall = {}
    player = { collides_with = [ "wall" ] }
}

The filter name (for example player) can then be assigned to actors. Use collides_with to list specific filters this filter should collide with, or collides_with_all_except to collide with everything except the specified filters.

Collision rule¶

Two actors A and B generate collisions if either of the following is true:

A’s filter has B in its collides_with set, or
B’s filter has A in its collides_with set.

Actor classes¶

Actor classes are used to specify simulation properties to apply to Actors. Define classes inside the actors object:

actors = {
    static = { dynamic = false }
    dynamic = { dynamic = true }
    keyframed = { dynamic = true kinematic = true disable_gravity = true }
    trigger = { trigger = true }
}

Common actor class properties:

linear_damping: resistance applied to linear motion; useful to slow down objects unaffected by friction.
angular_damping: resistance applied to angular motion.
dynamic: when true, the actor is simulated each frame by the physics engine. If false, the actor cannot move but just collide.
kinematic: when true, the actor is driven externally (animation or code) rather than by physics. Kinematic objects push dynamic objects away but are unaffected by them.
disable_gravity: disables gravity for the actor.
trigger: actor does not produce collision responses but still generates overlap events.