networked graphics building networked virtual environments and networked games chapter 11: latency...

Networked GraphicsBuilding Networked Virtual Environments and Networked GamesChapter 11: Latency and Consistency

LATENCY IMPACT

ClientA ClientB

CarA A=1, V=0

CarB

A=1, V=0

CarA A=1, V=1

CarA A=1, V=2

CarA A=1, V=3

CarB

A=1, V=1

CarB

A=1, V=2

CarB

A=1, V=3

CarA CarB CarA CarB

Can’t apply open state

Door is Open & Locked

ClientA ClientB

Lock Door OpenDoor

Door is Closed & Unlocked

Door is Closed & Locked

Door is Closed & Unlocked

Door is Open & Unlocked

ClientA ClientBServer

Shooter (PlayerA)

Target (PlayerB)

ClientA ClientBServer

Shooter (PlayerA)

Target (PlayerB)

DUMB CLIENT AND LOCKSTEP SYNCHRONISATION

Quake ClientA

ReadInput

Rendering

Quake Server

ReceiveInput

Simulate

Quake ClientB

ReadInput

Rendering

MouseKeyboard

DrawLists, Game State

MouseKeyboard

DrawLists, Game State

CONSERVATIVE SIMULATIONS

Doom ClientA

ReadInput

Rendering

ReceiveInput

SimulateDoom ClientB

ReadInput

Rendering

Receive

Input

Simulate

Doom ClientC

ReadInput

Rendering

ReceiveInput

Simulate

ClientA

MessageI

Client=B Time=11.1

MessageI+1

Client=C Time=13.5

MessageI+2

Client=B Time=13.6

MessageI+3

Client=C Time=18.0

MessageI+4

Client=D Time=18.2

ClientB

ClientC

ClientD

Message Queue

TIME

EventExplode is delay at ClientC until after EventFire

ClientA

ClientB

ClientC

EventFire

EventExplode

ClientA

ClientB

ClientC

EventFire (0,1,0)

EventExplode (1,1,0)

EventFire (2,1,1)

EventExplode (2,1,0)

OPTIMISTIC ALGORITHMS

ClientA ClientB

Lock Door

OpenDoor

ClientC

AddZombies

RemoveZombies

CloseDoor

t0

t1

t2

t3

t4

CLIENT PREDICT AHEAD

ClientA Server

P0 P1

MoveP0 to P1

Move?P1 to P2

Move?P2 to P3

Move?P3 to P4

Move?P0 to P1

MoveP1 to P2

MoveP2 to P3

P2P1

P3P2

P4P3

P0 P1

P2P1

P3P2

ClientA Server

P0 P1

MoveP0 to P1

Move?P1 to P2

Move?P2 to P3

Move?P0 to P1

FailMoveP1 to Q1

FailMoveP1 to Q1

P2P1

P3P2

Q1

P0 P1

Q1P1

P3P2Q1

EXTRAPOLATION ALGORITHMS

1st Order Model

2nd Order Model

a) Player model sending three

updates

b) Ghost model path without

blending

to

t1

t2

c) Old ghost model and new ghost

model at t1

d) Blending between the old ghost and new ghost

over several frames

e) Ghost model path with blending

a) Old ghost position at t0, new ghost position at t0 and

new ghost position at t0+t

t0

New ghost t0+t

New ghost t0

Old ghost t0

b) Dotted line shows the planned path toreach the target position and direction

a) Player model showing the timings of dead-reckoning updates at the peaks of a periodic motion

Update at t0

Update at t1

b) On arrival of an update message, the ghost model plans to converge the current ghost model position

with an extrapolation of the received position

Correct player model path

Convergence pathGhost model location at

t0

Player model update at t0

Extrapolation of player model

c) On the next update message the ghost model is out of phase with the player model. T

to

t1

Player model update at t1

a) Player model showing the object avoiding the

wall

Path of ghost model after update at t0

b) After the update at t1 the ghost model cannot

converge

2nd Order Model with Error Threshold

INTERPOLATION, PLAYOUT DELAYS AND LOCAL LAG

Sender Receiver

P1

P2

P3

P4

t1

t2

t3

t4

P0 P1 P2 P3

t0 t1 t2 t3

Interpolate P0→P1

Playout delay

Sender Receiver

P1

P2

P3

P4

t1

t2

t3

t4

t5

t6

t0 t1 t2 t3

Interpolate P0→P1

Maximum latency

P0 P1 P2 P3

Playout delay

Sender

ClientA

ClientB

t0 t1 t2 t3

Interval (Tα)

EA1

Playout delay (T)

ClientA

ClientB

ClientC

EC1 EC2

EB1 EB2

t4

PERCEPTION FILTERS

ClientAClientB

x position1.0

Tnetwork

Adde

d de

lay

Time

1.0

x po

sition

1.0 2.0

3.0 4.0

Time

1.0

x po

sition

1.0 2.0 3.0 4.0

a) Both clients’ view of the ball x position using temporal corrections

x position of ball as seen from ClientA

x position of ball as seen from ClientB

Time

1.0

x po

sition

1.0 2.0 3.0 4.0

b) Both clients’ view of the ball x position without using temporal corrections

x position of ball as seen from ClientB

x position of ball as seen from ClientA

REVEALING LATENCY