Client prediction

The slow step

Kai is 150 ms from the server. Kai presses walk. The input takes 150 ms to reach the server, and the server's answer takes 150 ms to come back.

If the app waits for that answer, every step starts 300 ms late, and the game feels like walking through mud.

Predict

With client prediction, the app runs the same movement code the server runs, at once, and shows the result.

Valve's Source does this: the client predicts its own player, and the server still has the final say. When the server answers, the app checks its guess.

Why the same code

The guess is right only if the app and the server run the same rules on the same inputs. Shard Garden shares one movement file between both.

Then a prediction is wrong only when something the app did not know about happened, like another player's action.

What is not predicted

The app predicts only its own player's actions. Other players are drawn from snapshots, slightly in the past.

Anything the server decides, like which seed a mystery pack holds, is never guessed: the app waits for the answer.

Hidden, not gone

Prediction does not shorten the trip to the server. It shows Kai the result before the server confirms it, so the delay is hidden.

Feel it

Next, plant a seed three ways with a server 300 ms away, and see what prediction changes.

Bolt says: Next: hands-on, feel the round trip.