DoubleDeez
commented
4 years ago I haven't fully read through this yet but I wanted to comment that I have a position synchronization class started for my own game that I'm planning to move to the framework. It supports prediction and interpolation based on the expected RPC rate but there's still a bunch of room for improvement.
References: https://www.reddit.com/r/godot/comments/8ch20v/help_with_node_sync_over_a_network/ https://gafferongames.com/post/snapshot_interpolation/
Beider
So I plan on adding the following piece of code to my project because I need it for myself, I will write it to my branch and you can optionally pull it over once it is done. I am posting this here in case someone has better ideas on how to do this.
Player Synchronization
A common issue in network games is to ensure all players are synched, in particular if a new player joins the game in the middle of a game. I think a lot of this could be automated to this end I am going to add a few new features.
The first thing added to this end will be the player synchronizer class I outlined in another issue I posted here. In short this will allow the server to know the ping and approximate game time of the other players games.
Synchronizer
I intend to add a synchronizer class that will be instanced by the MDGameSession when the MDGameSession is created, it will be a root node just like MDGameSession and it's task will be to handle network synchronization on join / leave between players. Along with also tracking game ticks.
The first thing I will add is a GameTick tracker, this will work on the game delta time and be customizable with a default of 100 ticks per second. I think this will help a lot as rpc messages can then contain the tick the message was sent. This will make it easier for the other clients to display things properly. Say you recieve the following
[Tick100] Postion Vector2(10,10) [Tick110] Postion Vector2(10,20) [Tick116] Fire bullet + angle whatever [Tick120] Postion Vector2(10,30)
Without the tick it is very hard to know when the bullet should be fired, particularly since the position of this object will most likely be a bit behind in the first place. Another thing that could happen is something like this,
[Tick100] Postion Vector2(10,10) [Tick110] Postion Vector2(10,20) [Tick120] Postion Vector2(10,30) [Tick106] Fire bullet + angle whatever
If you have already moved past tick 106 you could always write code to figure out what the position was at tick 106 and spawn the bullet there, then add some additional velocity to make it catch up or simply calculate what position it would be at by the time you recieve the message
Of course you can send the position with your bullet but in general being able to know when in the other game simulation something happened would be incredibly useful.
Player join synchronization
The synchronizer will have a second feature, it will also track every networked node and member that is created through the framework and marked as important. To this extent I would add a new parameter to the SpawnNetworkNode called bool AddToNetworkSynchronizer which will be default true.
The synchronizer will have an option to pause all clients on player join, so if a player joins while the game is in progress. The synchronizer will use the ticks system to tell all existing players to pause on a given tick in the future. While this is happening the list of nodes and members that need to be synchronized will already have been sent to the new player.
Once the game is paused the synchronizer will ensure all players have the updated values for all networked objects and members. It will send progress messages back to the server which will distribute to all clients. I also plan to add a simple UI scene that is used for this (that can be overriden) that would show the status of synchronization.
Once all players are at the same tick and everything is synchronized the server will send a message to all clients to restart the game in a few seconds. For this the PlayerSynchronization class mentioned above will be used to ensure the players are as synched as possible.
I think adding this will let the framework pretty much keep all players mostly in synch automatically. Of course the synchronizer will also introduce a bunch of new events regarding synchronization and may even be extended to detect major desynchs and pause the game to allow everyone to synch up.
Examples (& kind of tests)
I wish to add an Example folder with a few examples.
Basic MP setup This will be the base scene used for all other examples. The idea here would be to create some simple UI that can host / join games. That way people who want to use the framework could simply inherit from this scene or copy this scene to get a quick start.
Synchronizer Predictive Example I will make a predictive actor that simply travels in a random direction and bounces off the edge of the screen. Then it will spawn in a lot of them and maybe also a bunch of inactive ones as well just to give the synchronizer more work. The idea here will be to test / demonstrate the synchronizer and how it can keep clients in synch without much actual work. If it all works out any joining client should be synched and see the exact same thing as the server.
Interactive Rejoin Example This demo will have a simple player character (godot sprite) where the player can set some properties on it (like scale, position, random color). When a player leaves I will save the data about the sprite and when another player join they will be asked if they want to join as one of the leavers or a new player. The idea is to show off how you can store data from disconnecting players and allow for rejoin.
2D Shooter Example Top down 2D shooter where players can join whenever they want and be synchronized into the game. The game will show off how to do a lobby, start the game, join in progress. Basic hit detection on both client / server side. And how to interpolate properties to keep players in synch.
Once a player wins a map a new random map will be loaded. It will show how you can have joining players spawn in on any map while the game is in progress.
I also plan to make this example into a youtube tutorial as I recently started a youtube channel to do devlogs and tutorials. here is one where I talk about the MDFramework a bit.
Open Questions / Problems
The main problem I am having is I want to introduce an easy way to say that you want ticks with some member. Say you have player position and you want it to be tracked with ticks. Maybe even keep a history of values that you can access from the code so you don't always have to write code to keep a history. It would be nice to make this as easy as possible.
I have not yet decided on the best way to do this. If there are any suggestions for this that would be great.
I am probably starting on this tomorrow, if anyone has suggestions or think my solution is utter garbage and have a better solution then please let me know.