1 A Novel Page-Based Data Structure for Interactive Walkthroughs Behzad Sajadi Yan Huang Pablo Diaz-Gutierrez Sung-Eui Yoon M. Gopi

2 Outline  Page-Based Rendering  Data Fetching Algorithm  2-Factor Data Layout  Implementation and Results  Summary  Conclusion and Future Work

3 Traditional Rendering Workflow

4 Page Based Rendering Workflow

5 Page Format  Self contained information Less bytes for vertex indices Effective compression # vertices # faces List of vertices with attributes List of vertices with attributes Indexed triangle list with attributes Indexed triangle list with attributes

Eliminating fragment accesses 6 Traditional K-d treePage based K-d tree Storage OS cache Process heap space High data management cost No data management cost  Low data management cost

7 Major Steps of the Workflows  Traditional rendering workflow  Page based rendering workflow Scene Data structure Layout Approximated scene Data structure

8 Advantages  Less space required for the data structure K-d tree on pages instead of triangles  Independence of the layout and data structure Any layout can be converted to the page based format

9 Outline  Page-Based Rendering  Data Fetching Algorithm  2-Factor Data Layout  Implementation and Results  Summary  Conclusion and Future Work

10 Rendering Flow K-d tree structure Render Fetch data Page numbers after VF Culling Triangles

11 Sorting the Page Numbers  Access pattern is based on storage …... K-d tree without sorting …... 1,72,54,125,79,148,16 1, 2, 4, 5, 7, 8, 9, 12, 14, 16 K-d tree after sorting 1,72,54,125,79,148,16

12 Rendering Flow K-d tree structure Sort page numbers Render Fetch data Page numbers after VF Culling Triangles 1, 2, 4,

13 Backface Culling

14 Rendering Flow K-d tree structure Sort page numbers Render Fetch data Backface Culling Page numbers after VF Culling Triangles 1, 2, 4,

15 Outline  Page-Based Rendering  Data Fetching Algorithm  2-Factor Data Layout  Implementation and Results  Summary  Conclusion and Future Work

16 Related Works  Cache oblivious layout by Yoon et al. [2006]  Space filling curves Morton layout (Z-Order) Hilbert layout

17 Graph Construction  Nodes: Group of triangles  Edge weights: Distance between the primitives of the nodes

18 Steps of the Method  Use GLA (Generalized Lloyd's Algorithm) to partition the primitives  Use [Diaz-Gutierrez and Gopi 2005] to get a 2-factor  Iterate in a hierarchical manner

19 The Layout Hierarchy Ordering using 2-Factor Layouts Partitioning using GLA clustering Final Layout:

20 Advantages  Operates globally  Scalable  Amenable for multiple proximity measures

21 Outline  Page-Based Rendering  Data Fetching Algorithm  2-Factor Data Layout  Implementation and Results  Summary  Conclusion and Future Work

22 The City Model  Floor planned using role playing city map generator 5.40

23 The City Model (Contd.)  3D models of houses and trees were replaced  Cars were added in the streets

24 The City Model (Contd.)  Specifications 110 million triangles 90 million vertices Spans 4528 MB Around 10,000 objects 115 million vertices in page format Spans 3814 MB in page format

25 Texture Based Simplification [Aliaga and Lastra 1997]

26 Statistics  Frame rates Raster scan layout: 20 FPS Cache oblivious layout by Yoon et al. [2006]: 27 fps 2-factor layout: 28 FPS  Rendering statistics (our layout) Page size: 4 KB Average disk-page per frame: 2365 Average triangle per frame: 240 K

27 Statistics (Contd.)  Computation times Page format conversion: 15 min (Offline) K-d tree construction: 5 min (Offline) Billboard rendering: 20 hour (Offline) Program initialization: 20 sec  Consumed memory Billboards: 640 MB K-d tree: 96 MB (including bounding boxes and normal cones)

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29 Outline  Page-Based Rendering  Data Fetching Algorithm  2-Factor Data Layout  Implementation and Results  Summary  Conclusion and Future Work

30 Before Rendering (Offline) Steps Given layout Convert to the page format Construct the disk-page hierarchy

Rendering (Online) Steps K-d tree structure Sort page numbers Render Fetch data Backface Culling Page numbers after VF Culling Triangles 1, 2, 4,

32 Outline  Page-Based Rendering  Data Fetching Algorithm  2-Factor Data Layout  Implementation and Results  Summary  Conclusion and Future Work

33 Conclusion  A simple data structure on the disk pages Simplicity High Performance Generality  A new cache oblivious layout

34 Future Work  Analyzing the disk-page hierarchy on other data structures  Exploring other applications that can make use of this data structure  Including simplification techniques  Adding a cache management system  Analyzing the number cache hits and misses

35 Questions?