Netgames

[LocalInsomniac]

Reimplement netgames using lockstep which is more suitable towards PNEngine's structure.

Reference

• https://yal.cc/preparing-your-game-for-deterministic-netcode/
• https://zdoom.org/wiki/Multiplayer#Technical_details

Desyncs could be detected by comparing game/level information periodically, for example.

[LocalInsomniac]

Goal 1 (Complete)

Create a tick queueing system. Clients will be using this to tick the game with input relays from the host. Currently, only the host should be able to control their character. Client input will be handled later.

Steps

• Every game tick, AFTER player input is read, the host will send a reliable TICK packet containing the input data of every player in the game.
• Once the client has received the packet, it will be ACKed and added into the tick queue.
• If a client's game's local ticks accumulate up to 1 or more, the amount of ticks to advance will be overridden by the amount of ticks that have been queued. The game will then tick and override player inputs until the queue is empty.

[LocalInsomniac]

Goal 2 (Complete)

Allow each client to send input data to the host. The host should then queue those inputs in the Networking Async Event and apply it to the next tick.

Steps

• After ALL queued ticks have been advanced in a client, send the client's input state to the host regardless of if nothing was pressed. (Should it be a reliable packet?)
• Once the host has received the packet, it will then store that state in the client's input queue.
• If any remote player's queue is not empty, their previous input state will be stored and their new state will be fetched from the queue on the next tick.

[LocalInsomniac]

Some other ideas to consider:

• Support demo recording on the clients' side. Currently, only the host can record demos properly whereas clients will see no input.
• Client-side prediction. It is very unlikely, but would be perfect for stuff like mouselook.
• Text chat.

[LocalInsomniac]

Goal 3 (Complete)

Implement game stalling by checking if any client hasn't ACKed tick packets for more than a certain amount of ticks (should be around half of TICKRATE). This should help laggy clients catch up with other players, otherwise they would be stuck on a frozen game that occasionally skips forward.

Steps

A naive implementation would be as follows:

• Netgame gets two new variables: ack_count for tracking how many clients have ACKed any tick packet, and stall_time for increasing the timer before stalling the game.

  • Each client (NetPlayer) also gets a boolean variable named tick_acked in order to increment the counter properly.

• At the start of the host's tick loop, check if ack_count >= player_count.

  • If true, reset ack_count and stall_time and set every client's tick_acked to false.
  • If false, increment stall_time. If stall_time reaches the limit, the game is paused until all clients have ACKed.

• If a client has ACKed a tick packet during a Network Async Event while their tick_acked is false, it is set to true and ack_count is incremented.