Smooth Control and Networking

Smooth movement is one of the hardest things in a networked action game: there's always a delay between your screen and the server, and you can't remove it — only hide it. This is the third and final post in the series catching the story up to 0.11.5, and it's about how we hid that delay to make the ship feel alive.

There used to be a delay the size of your ping between pressing a key and the ship moving: you'd press, then wait for the server to confirm. On a calm connection that's bearable, but as soon as the ping grew the ship started to feel mushy — as if your commands reached it late.

Now the client no longer waits for the server's reply to move the ship: your input is applied to it instantly, and the server just quietly confirms everything in the background. Acceleration, turning, braking happen the moment you ask for them — control no longer depends on how far away the server is.

Since the ship moves on your screen before the server knows about it, the two pictures inevitably drift apart a little. The question is what happens when the server sends its own, authoritative version. The ship used to just jump to the server's position — a sharp yank, as if pulled by a string.

Now the mismatch isn't fixed in a single jump: the ship is eased toward where it's supposed to be over a few frames, and the eye barely catches it. We also separated rotation from position — a positional correction no longer twists your aim sideways.

The most noticeable case of its own is collisions. Other ships and wrecks are shown on your screen with a small delay — essentially a little in the past. A hit against them used to be resolved only on the server: you'd fly into a bot that stood still for you, the ship would simply stop dead, and the reaction to the contact would arrive only after the delay. Now the client plays the collision out at once, right on your screen: the impact feels immediate and physical, and the picture then eases back into line with the server's, without a sharp snap.

Ping is almost never steady: packets arrive with uneven gaps, and the delay keeps spiking and settling again — this is what's called jitter. To show other ships smoothly, the client holds the picture at a small delay and constantly tunes it to the current ping. It used to do that tuning in jerks, whole frames at a time: on every change of ping the scene stuttered in little steps, as if it were being tugged back and forth.

Now the client does the tuning smoothly — instead of steps it gently draws the picture along, and you can barely notice it. The staircase stutter on ping spikes and recovery is gone, and the motion stays even.

Last time we were fixing the projectile itself — so that a fast round wouldn't slip through a target between frames. This is about something else: the delay between you and the server. Because of ping, what you see is slightly in the past, and the honest question of networked combat sounds like this: if the enemy was squarely in your sights on your screen, will the hit count, even though on the server it has already moved by then?

Now it does. At the moment you fire, the server rewinds the world back to the frame you saw and checks the hit against it. Your ping no longer steals the hits you earned: where you aimed on your screen is where it lands. The rewind has a sensible limit, so it stays fair to the one being shot at too.

That wraps up our story about version 0.11.5. All three parts were about the foundation — client, combat, and networking — that the game rests on. From here we'll start talking about the game mechanics themselves that will go into the first playable alpha: the core loop of warping into sector instances, mining resources, fighting pirates and other players, loot and repairs at the station, and progression through ships and modules. More on that in upcoming posts.