rigid_body_gravity
Gravity is such a common force that it is implemented as a special case (even if it could easily be implemented
by the user using force application). The gravity is given to the constructor of the physics World. It can be modified by modifying the
field World.gravity. Note however that a change of gravity won't automatically wake-up the
sleeping bodies so keep in mind that you may want to wake them up manually before a gravity change.
Because fixed and kinematic bodies are immune to forces, they are not affected by gravity.
A rigid-body with no mass will not be affected by gravity either. So if your rigid-body doesn't fall when you expected it to, make sure it has a mass set explicitly, or has at least one collider with non-zero density attached to it.
It is possible to change the way gravity affects a specific rigid-body by setting the rigid-body's gravity scale
to a value other than 1.0. The magnitude of the gravity applied to this body will be multiplied by this scaling
factor. Therefore, a gravity scale set to 0.0 will disable gravity for the rigid-body whereas a gravity scale set to
2.0 will make it twice as strong. A negative value will flip the direction of the gravity for this rigid-body.
This gravity scale factor can be set when the rigid-body is created or after its creation:
/* Set the gravity scale when the rigid-body is created. */
let rigidBodyDesc = RAPIER.RigidBodyDesc.dynamic()
.setGravityScale(2.0);
let rigidBody = world.createRigidBody(rigidBodyDesc);
/* Set the gravity scale after the rigid-body creation. */
rigidBody.setGravityScale(2.0, true);