Doom3world

I wonder if there are people out there willing to join in rewriting Doom3's netcode from currently "extrapolated" (forward prediction) snapshots to "interpolated" snapshots. The idea is to make Doom3's internet clientside network performance less vulnerable to latency towards the game server...

These two videos showcase what difference a change of the netcode is having on the clientside gaming experience (click the images below to playback the videos):








It would be great being able to get enough capable people together to pull this off...

That's quite the difference.

Neat.

How would this work for increased use of physics & scripting over the network?

In fact going for interpolation would improve performance on pretty much every level since extrapolating the snapshots is really CPU intense. When running Doom3 in interpolated mode I get a solid 33% FPS performance increase...

Is that a server side performance increase? Could a standard D3 client connect to an optimized server?

No. The client and server would have to be running custom code.

From iddevnet.com:



So as simulation says, clients would require the same codebase update as the server...

awww bummer. I was hoping for a R1Q2 like solution to Doom 3's netcode.

Also, keep in mind that just because the movement is nice and smooth doesn't mean the players are in the right place - with that build you presumably need to lead your shots by your latency, which you don't with d3 base. There will be other negative effects too, such as the local player view not being as correct wrt the server view.

The d3 method works pretty well for pings up to ~100, and these days, do you really need to play on 400?

I see lots of Quake 2 players with 200+. Seems most of the Doom 3 community it outside the USA (or at least the bulk of the players & content creators) so a relatively high ping is still a concern.

I live in South Africa.

My ping to london is about 220ms and to the US east cost about 240 - 270ms. Before xbox live was officially launched in south africa I use to play Battlefield bad company 2 on the overseas servers. Except for some minimal lag with the rocket launchers the game runs smooth.
Quake wars and doom 3 is completely unplayable with pings above 120ms. Characters jumping around getting stuck in corners it is horrible. More stable net code would be wonderful. Also for modding you can focus more on co-op games.

There is a good reason why the majority of fps games use interpolation instead of Forward Prediction. Forward Prediction actually attempts to do the impossible by trying to predict on a game client what the server's gameworld looks like at the very moment. But since every game client (even the ones in a LAN environment at 0ms Latency) always runs with a certain delay behind the server, there are always going to happen prediction errors, which then, when the confirmed snapshots from the server finally arrive, have to be corrected. We are experiencing these corrections as "snapping". And I am witnessing that kind of snapping even at the LAN environment where actually the latency is very low.

A 100ms server radius, like you define as pretty fine, (which in fact it isn't, as there is already a lot of snapping happening for all the game entities and also a lot of skipping for the particle & projectile effects spawning) actually narrows down the server's client pool quite heavily, compared to a game server that can offer acceptable gameplay for clients with a ping of up to 400ms, like visually illustrated in the below images for a server located in London.

Server Client Coverage at 100ms


Server Client Coverage at 400ms


And finally I would like to add that I rather prefer to lead my aiming (or have the shooting be current and then later backwards calculated like in CSS with "unlagged") than shooting at a jerking-snapping-teleporting target where I barely can make up where it actually is located like showcased in this youtube movie. After all there is a reason why multiplayer-only game developer Splash Damage introduced interpolation networkcode with Brink to idtech4.

Another issue with the D3 tech way is the "springback" when you're ping gets to high. Because it's anticipating where you should be and the latency is so high, the client does something but the server never uses that info and you never end up firing, never move (spring back to position), etc.

The other way will compensate for this but makes things more inaccurate. I prefer the old way myself, as someone who's ping can occasionally spike (the old way causes "springback" too but not as bad and you need a much higher ping).

Hey devils, a cvar to let the server choose would be awesome!

THIS wikipedia article gives a nice sum up of the pro and cons of both methods: