how frag-x works

a server is started

it initializes a simulation which can be accessed globally
it starts a thread called listener which waits for new players to join

this thread spawns new threads called client_listener for each connected player which has access to the simulations input_messages (a thread safe queue)

it starts a thread called server_messager which has access to the simulations output_messages, which is also a thread safe queue

a client is launched

it makes a connection to the server
the listener thread adds a player to the server simulation and starts a client_listener thread
the client starts receiving snapshots of the game simulation and is able to draw the player on the screen

you are interacting with the game using input devices and the game state is changing

the client samples these input devices and sends it over as a PlayerStateMessage
the server's client listener thread gets a PlayerStateMessage and adds it the Simulation's input_messages
the simulation is ticking at a rate defined by SERVER_TICK_RATE_HZ, the way we perform a tick in general is by calling a method that we define called step

for example, at the top level of the server there is something that calls the global simulations step method

this method in turn will call step functions of the objects that are involved in the simulation, these objects are all children of SimulationObject

after the step function is done, the server will have consumed the information that you provided from your keyboard and mouse, and determined what the game should now look like, it then adds a GameStateMessage to output_messages

a GameStateMessage is just enough information to draw the player on the client

the server_messager thread has been waiting for something to appear in output_messages, and so now it can get from that queue and sends it across the network back to the player
the client stores this message as a simulation_state, and it is drawn to the screen at a rate of FPS until a new simulation_state appears