Ive been working on a prototype for client side prediction in multiplayer games, Ive managed to make it work but for some reason the prediction breaks when the latency fluctuates.
For example if I have a constant 200ms latency, client side prediction works just fine, but it starts doing weird things when latency fluctuates, first I tought it may have to do with packages arriving out of order (packets have an ID) but discarding duplicates / out of order packets didnt really change anything.
The purple point represents the position received from the server and the yellow one the predicted position based on the one received + all non processed inputs.
Client Moving with constant 400ms latency: 
Client Moving with only 200ms latency (but fluctuates +-25ms): 
Code for the client movement (prediction, called every frame):
private void Predict(float delta) { instruction_count++; byte instruction = PlayerMovement.ReadInput(); network.SendClientMovementInstructions(instruction_count, instruction); instructions.Add(new Instruction{tick = instruction_count, data = instruction}); Position += PlayerMovement.Movement(instruction, delta); } Code for the reconciliation (this is called when a package arrives from the server):
private void Reconciliate(int tick, Vector2 received_position) { Vector2 prediction = received_position; foreach(var entry in instructions) if (entry.tick >= tick) prediction += PlayerMovement.Movement(entry.data, 1.0f / 60.0f); instructions.RemoveAll(i => (i.tick < tick)); //i dont use it here but if this goes past certain threshold we snap back the client to were it should be. float deviation = (prediction - Position).Length(); } 