Stateless generation of distributed virtual worlds

1. STATELESS GENERATION OF
DISTRIBUTED VIRTUAL WORLDS
JIŘÍ DANIHELKA, LUKÁŠ KENCL, JIŘÍ ŽÁRA

2. Motivation
 Complex 3D virtual world shared on multiple
mobile devices
– the devices cannot store the whole world
(the world can be potentially infinite)
– the world is generated on-demand based on view frustum
– we used infinite virtual cities as our main use case
– the mobile devices has to show the same geometry
– the devices has to work even when disconnected
Stateless Generation of Distributed Virtual Worlds

3. Paper idea
 How the problem can be solved
– mobile devices will share the same pseudo-random generator
(share the same seed)
– each device will generate the content of its view frustum
– the content is consistent does not depend on previously generated
geometry or states of other clients
– can work even offline
– we call our method “Stateless generation”
Stateless Generation of Distributed Virtual Worlds

4. Final result
Stateless Generation of Distributed Virtual Worlds

5. CityEngine CGA grammars
Stateless Generation of Distributed Virtual Worlds

6. Building modeling
Stateless Generation of Distributed Virtual Worlds

7. Transforming building to CGA grammer
Stateless Generation of Distributed Virtual Worlds

8. City generation pipeline
Stateless Generation of Distributed Virtual Worlds

9. Cars 2
Stateless Generation of Distributed Virtual Worlds

10. Related work
 Aliaga, Vanegas, Beneš:
Interactive Example-Based Urban Layout Synthesis
Stateless Generation of Distributed Virtual Worlds

11. Related work
 Aliaga, Vanegas, Beneš:
Interactive Example-Based Urban Layout Synthesis
Stateless Generation of Distributed Virtual Worlds

12. Related work
 Greuter S., Parker J., Stewart N., Leach G.
Real-time procedural generation of pseudo-infinite cities
Stateless Generation of Distributed Virtual Worlds

13. Our approach
 Delaunay triangulation
 But can we do this on an infinite grid?
Stateless Generation of Distributed Virtual Worlds

14. Our approach
 Delaunay triangulation - proof
Stateless Generation of Distributed Virtual Worlds

15. Street segment interfaces
 Generated consistently using a hash function
 Cannot be overlapping
Stateless Generation of Distributed Virtual Worlds

16. Stateless generation
 Creating street nodes
(inspired by ray-tracing sampling)
Stateless Generation of Distributed Virtual Worlds

17. Stateless generation
 Creating possible street segments
Stateless Generation of Distributed Virtual Worlds

18. Stateless generation
 Minimum weight path
 Angles can be transformed to edges using
the graph’s dual form called “line graph”
Stateless Generation of Distributed Virtual Worlds

19. Stateless generation
 Lot generation
Stateless Generation of Distributed Virtual Worlds

20. Stateless generation
 Variations of street layout
Stateless Generation of Distributed Virtual Worlds

21. Measurements
 Stateless approach is not too demanding
Stateless Generation of Distributed Virtual Worlds

22. Measurements
 Rendering speed on a mobile phone (Lumia 920)
Stateless Generation of Distributed Virtual Worlds

23. Examples
 Big city
Stateless Generation of Distributed Virtual Worlds

24. Examples
 Antic Greece town
Stateless Generation of Distributed Virtual Worlds

25. Examples
 City suburbs
Stateless Generation of Distributed Virtual Worlds

26. Conclusions
 Advantages
– infinite worlds generated on-demand
– consistent geometry in case of multiple clients
– cities look more natural compared to previous work
– can be used for scalable tasks (in cloud)
 Drawbacks:
– only for static content
– path adding algorithm is greedy
– currently only one level of streets
Stateless Generation of Distributed Virtual Worlds

27. Thank you for attention
Jiří Danihelka
danihjir@fel.cvut.cz
Stateless Generation of Distributed Virtual Worlds