|fixture||the id of the bound fixture|
When you bind a fixture to an instance using physics_fixture_bind this
returns an "id" for the bound fixture. You can use this id to get
the restitution (the "bounciness" property) value of the bound
fixture, not the "base" fixture, at any time using this
var rest = physics_get_restitution(fix_id);
physics_set_restitution(fix_id, rest * 2);
The code above gets the current restitution value for the bound physics properties of the instance and then sets them to a different value.