Local Perception Filter

Transcription

1 Local Perception Filter 1

2 A S B With Time Sync 2

3 A S B Without Time Sync 3

4 Maintaining tightly synchronized states 4

5 States can go out of date. A player sees a state that happened t seconds ago. 5

6 Hybrid Model: Render objects within realtime interaction range in real time, other objects in delayed time. 6

7 happening now A B happened time t ago 7

8 Question: What if a player A throws a ball at player B? 8

9 happening now A B happened time t ago 9

10 Question: What if a player B throws a ball at player A? 10

11 happening now A B happened time t ago 11

12 Two Kinds of Entities Active: players (unpredictable) Passive: ball, bullet (predictable) 12

13 A happened t ago happened t - 1 ago happened t - 2 ago B 13

14 Question: What if a player A throws a ball at player B? 14

15 A happened t ago happened t - 1 ago happened t - 2 ago B 15

16 Question: What if a player B throws a ball at player A? 16

17 A happened t ago happened t - 1 ago happened t - 2 ago B 17

18 B throws ball at A. A sees that the ball s speed increases as it gets nearer to A. 18

19 A throws ball at B. A sees that the ball s speed decreases as it gets away from A. 19

20 A B Server not shown in this example. 20

21 From perspective of a player A, the other player is surrounded by a temporal distortion field defined by the communication delay between that player and A. 21

22 1D temporal distortion field from A s perspective. temporal distortion A B rendered position of ball 22

23 1D temporal distortion field from B s perspective. temporal distortion A B rendered position of ball 23

24 Extension to multi players temporal distortion A C B rendered position of ball 24

25 Limitations Delay jitter leads to fluctuating field. Can t interact directly with other players. 25

26 Local Perception Filter 26

27 Bullet Time 27

28 Slow down time to allow more reaction time. E.g. Max Payne 28

29 Difficult in multiplayer game -- naive implementation slows every player down. 29

30 Ideally, players who invoke bullet time slow down their game, but others play on. 30

31 bullet time -- bullet slows down as it comes near the player; increases speed as it moves away. 31

32 bullet time distortion field from B s perspective. temporal distortion A B rendered position of ball 32

33 overall distortion field temporal distortion A B rendered position of ball 33

34 overall distortion field from B s perspective. temporal distortion A B rendered position of ball 34

35 bullet time distortion field from A s perspective. temporal distortion A B rendered position of ball 35

36 You Are Here CS4344 Client/Server Architecture Synchronization Protocols 36

37 You Are Here CS4344 Client/Server Architecture Synchronization Protocols Interest Management 37

38 Bandwidth Requirement 38

39 A Measurement Study of Shen Zhou Online, an MMORPG. Images taken from 39

40 7 kbps Average bandwidth per client 40

41 2.5 : 1 Peak-to-Mean Ratio for Bandwidth 41

42 370,000 Simultaneous Number Of Players (Ragnarok Online, December 2004) 42

43 6.5 Gbps Peak Server Bandwidth 43

44 860 Terabyte Amount of data transfered per month 44

45 Need to reduce bandwidth overhead 45

46 Dead Reckoning 46

47 Interest Management 47

48 Relevance Filtering 48

49 Idea: only need to update another player p if the update matters to p. 49

50 Aura / Area-of-Interest 50

51 Update of p matters to q if the auras of p and q intersect. 51

52 Foci (what a player can see) 52

53 Nimbi (where a player can be seen) 53

54 Update of p matters to q if the foci of p intersects nimbi of q. 54

55 Calculating aura/foci/nimbi can be costly. 55

56 Idea: approximate use bounding boxes 56

57 or approximate using cells 57

58 Large cell: Redundant messages. Small cell: Large management overhead. 58

59 The white player will receive many messages he/she is not interested in. 59

60 Idea: we can dynamically partition the cells into smaller ones as needed. 60

61 Generalization: an entity may specify any other events/ entity it is interested in. 61

62 Communication Abstraction 62

63 Multicast: send a message to a set of subscribers 63

64 Group: a channel to publish messages 64

65 A client can subscribe to/ join a group to start receiving messages from that group. 65

66 A client can unsubscribe from/leave a group to stop receiving messages from that group. 66

67 Anyone can send a message to a group (need not be a subscriber). 67

68 a group a subscriber 68

69 Each cell is a group. A subscriber can subscribe to multiple cells. A group can have multiple publishers. a group 69

70 Implementation: IP Multicast 70

71 Multicast groups are identified using class D IP addresses ( to ) 71

72 Any message sent to a multicast address will be sent to all its subscriber. 72

73 Anyone listening to a multicast address will receive messages sent to it. 73

74 Problems with IP Multicast 74

75 Not reliable 75

76 join/leave takes time 76

77 not widely deployed 77

78 need states at the router 78

79 and many others.. 79