Groups Rooms together to allow common functionality.
Although Room behavior can be specified individually, sometimes it is faster and more convenient to write functionality for a group of rooms.
A RoomGroup can for example be used to specify Rooms that are outside, and switch on or off a directional light, sky, or rain effect as the player enters / exits the area.
RoomGroups receive gameplay callbacks when the
gameplay_monitor is switched on, as
notifications as they enter and exit the gameplay area (see RoomManager for details).
int roomgroup_priority =
When the Camera is within more than one room (regular and internal), the higher priority room will take precedence. So with for example, a house inside a terrain 'room', you would make the house higher priority, so that when the camera is within the house, the house is used as the source room, but outside the house, the terrain room would be used instead.