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https://github.com/marcello505/godot-ggrs-wrapper

A Rust GDNative project to provide GGRS to the Godot Engine
https://github.com/marcello505/godot-ggrs-wrapper

gamedev gdnative ggrs godot godotengine rollback rollback-netcode rust

Last synced: about 1 month ago
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A Rust GDNative project to provide GGRS to the Godot Engine

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# godot-ggrs-wrapper



The purpose of this repo is to create a wrapper for the [ggrs](https://github.com/gschup/ggrs) Rust crate so that this can be used inside the Godot Game Engine. To accomplish this the [godot-rust](https://github.com/godot-rust/godot-rust) GDNative bindings are used. Although the project currently implements all of the GGRS features, **i can't guarantee** that it's ready for use in production.



## Notes



- It's recommended that you set `reloadable` to `false` inside the `GDNativeLibrary` Godot resource.

- Tested on Godot version 3.3.2, Godot 4.0 will have vastly expanded GDNative capabilities so when that comes out it can be assumed that this project will break.

- Inputs to GodotGGRS is currently in the format of a unsigned 32-bit integer.

- States are GodotByteArrays, you convert the godot variant to a ByteArray and give it to GodotGGRS.

- Compiling requires Clang, see details [here](https://rust-lang.github.io/rust-bindgen/requirements.html).



## Links



- [Documentation](https://docs.rs/godot-ggrs-wrapper/)

- [Crates.io](https://crates.io/crates/godot-ggrs-wrapper)



## Examples



- [Remote connection between 2 different machines](https://youtu.be/8gwXVMqhNs8)

- [Example Project](https://github.com/marcello505/godot-ggrs-wrapper/tree/main/example)



## Projects that use godot-ggrs-wrapper



Does your project use godot-ggrs-wrapper? Let me know and i'll be happy to add a link!



- [Girls With Swords](https://github.com/trian-gles/Girls-with-swords-GGRS)



## Quick start



Since this project uses [godot-rust](https://github.com/godot-rust/godot-rust) GDNative bindings you should be familiar with how to set up a godot-rust GDNative node inside Godot. If you aren't please check out [this page](https://godot-rust.github.io/book/getting-started/hello-world.html) for details. The setup you want to have is a scene with a node that has the GodotGGRSP2PSession class bound to it.



### Starting a session with GodotGGRSP2PSession



To set up a session you want to have a script that addresses the GGRS node. Just having the node inside your scene doesn't create a session for you. Here i took the root node to make a script that makes a session on the **\_ready()** function



```gdscript

func _ready():

	var local_handle: int #This var is later used to identify your local inputs

	var remote_handle: int #This var is later used to identify the remote_players inputs

	if(OS.get_cmdline_args()[0] == "listen"):

		$GodotGGRS.create_new_session(7070, 2) # Port 7070, 2 max players, max 8 prediction frames

		local_handle = $GodotGGRS.add_local_player()

		remote_handle = $GodotGGRS.add_remote_player("127.0.0.1:7071")

	elif(OS.get_cmdline_args()[0] == "join"):

		$GodotGGRS.create_new_session(7071, 2) # Port 7071, 2 max players, max 8 prediction frames

		remote_handle = $GodotGGRS.add_remote_player("127.0.0.1:7070")

		local_handle = $GodotGGRS.add_local_player()



	$GodotGGRS.receive_callback_node(self) # Set the node which will implement the callback methods

	$GodotGGRS.set_frame_delay(2, local_handle) # Set personal frame_delay, works only for local_handles.

	$GodotGGRS.start_session() #Start listening for a session.

```



As you can see we swap the order of adding players depending on who's the "host". In reality since it's a peer 2 peer library, there is no true host. However you should have a way to distinguish between player 1 and player 2.



### Advancing frames



Now that we have a session we want to start implementing our loop. Godot's default **\_process()** and **\_physics_process()** will serve us nicely here.



```gdscript

func _process(_delta):

	$GodotGGRS.poll_remote_clients() # GGRS needs to periodically process UDP requests and such, sticking it in \_process() works nicely since it's only called on idle.



func _physics_process(_delta):

	if($GodotGGRS.is_running()): # This will return true when all players and spectators have joined and have been synched.

		$GodotGGRS.advance_frame(local_handle, raw_input_to_int("con1")) # raw_input_to_int is a method that parses InputActions that start with "con1" into a integer.



func raw_input_to_int(prefix: String)->int:

	# This method is how i parse InputActions into an int, but as long as it's an int it doesn't matter how it's parsed.

	var result := 0;

	if(Input.is_action_pressed(prefix + "_left")): #The action it checks here would be "con1_left" if the prefix is set to "con1"

		result |= 1

	if(Input.is_action_pressed(prefix + "_right")):

		result |= 2

	if(Input.is_action_pressed(prefix + "_up")):

		result |= 4

	if(Input.is_action_pressed(prefix + "_down")):

		result |= 8

	return result;

```



Calling advance_frame will tell GGRS that you are ready to go to the next frame using the input you've given as a parameter. GGRS will do it's thing and callback to Godot once it's ready to continue.



### Handling GGRS callbacks



So how to handle GGRS callbacks is alot more subjective than the steps before and will vary greatly on how your game is built. The only thing required is that you implement the callback functions, but the logic inside can be pretty much anything to fit to your game. Here's how i implemented the callback methods.



```gdscript

func ggrs_advance_frame(inputs: Array):

	# inputs is an array of input data indexed by handle.

	# input_data itself is also an array with the following: [frame: int, size: int, inputs: int]

	# frame can be used as a sanity check, size is used internally to properly slice the buffer of bytes and inputs is the int we created in our previous step.

	var net1_inputs := 0;

	var net2_inputs := 0;

	if(local_handle < remote_handle):

		net1_inputs = inputs[local_handle][2]

		net2_inputs = inputs[remote_handle][2]

	else:

		net1_inputs = inputs[remote_handle][2]

		net2_inputs = inputs[local_handle][2]

	int_to_raw_input("net1", net1_inputs) # Player objects check for InputActions that aren't bound to any controller.

	int_to_raw_input("net2", net2_inputs) # Player objects check for InputActions that aren't bound to any controller.

	_handle_player_frames()



func ggrs_load_game_state(frame: int, buffer: PoolByteArray, checksum: int):

	var state : Dictionary = bytes2var(buffer);

	P1.load_state(state.get("P1", {}))

	P2.load_state(state.get("P2", {}))



func ggrs_save_game_state(frame: int)->PoolByteArray: # frame parameter can be used as a sanity check (making sure it matches your internal frame counter).

	var save_state = {}

	save_state["P1"] = _save_P1_state("");

	save_state["P2"] = _save_P2_state("");

	return var2bytes(save_state);



func int_to_raw_input(prefix: String, inputs: int):

	_set_action(prefix + "_left", inputs & 1)

	_set_action(prefix + "_right", inputs & 2)

	_set_action(prefix + "_up", inputs & 4)

	_set_action(prefix + "_down", inputs & 8)



func _set_action(action: String, pressed: bool):

	if(pressed):

		Input.action_press(action)

	else:

		Input.action_release(action)



```



## Handling Rust Panics



Create a godot script containing the following:



```gdscript

extends Node



func rust_panic_hook(error_msg: String) -> void:

    assert(false, error_msg)

```



Make the Godot Project autoload this script as a singleton using the following name: "RustPanicHook". Now all Rust panics should always be catched properly. This solution is based off of the [Godot-Rust - Rust Panic Hook Recipe](https://godot-rust.github.io/book/recipes/rust_panic_handler.html).