hierarchical data structures for efficient rendering and navigation

G. Müller, Dagstuhl Seminar 00251, 19/06/2000

1ComputerGraphics, TU Braunschweig

Hierarchical Data Structures for Efficient Rendering and

Navigation

Gordon Müller

Computer Graphics

TU Braunschweig



Overview

• Framework for Efficient Rendering Techniques

• Object Hierarchies for Visibility Culling / Rendering / Radiosity / Raytracing / ...

• Automatic Hierarchy Creation• System Architecture• Navigation• Conclusions



Visibility Culling

• Design goals• conservative culling• dynamic scenes• real 3D• memory efficient• fast pre-processing

occluded

culled



Visibility Culling using Object Hierarchies

• Given any object hierarchy, perform conservative visibility test at inner scene nodes when traversing the graph based on bboxes

1

2

3

4

56

78

7

5 3 46 1 2 8



Culling

• Conservative view-frustum test (inside, outside, partially)

• Conservative occlusion test (occluded, partially visible)

• Occlusion test: hierarchical occlusion maps, OpenGL extensions, ...

• Occluder selection: ray casting samples• Traversal order: OpenGL select mode• Avoid unnecessary tests!



Culling Test (De-)Activation

• Disable culling test on failure (i.e. bbox visible)

• Enable culling test by using an oracle• 2-pass algorithm for every frame

I. if (node.activated)visibility test;if (visible(node)) node.activated =

false;recurse(node.childs);

II. Oracle activates nodes



Activation Oracle

• Currently• Re-activation after inode frames• Global activation temperature based on activation

success

• Work in progress• Frame rate analysis• Optimizations for static and/or particular (ie 2½ D)

environments



Visibility Culling Results

• Performance gain in framerate: 5-50% compared to naive culling at every scene node

• Elimination of ~75% of unsuccessful tests• Method adapts well to different scene types• Slightly higher frame rate variance• Good object hierarchies are essential for

efficient culling performance!



Demo

• Frankfurt• molecules



Bounding Volume Optimization I• Recursively subdivide the set of objects into

two disjoint sub-scenes• Objects are sorted along coordinate axes• No fixed subdivision position...



Bounding Volume Optimization II

• …instead, we minimize a cost function describing the approximate traversal costs

• Greedy optimization• Object-specific costs• O(n logn) total construction time on average

C B C B p B B C BH ii

n

i i

1

,



Object Hierarchy Results

• Tight hierarchical bounding volumes• Automatic separation of distant objects• Run-time efficient• Automatic detection of homogeneous

geometric detail (detects object clusters)



Objects

• Methods• void render(view*=NULL, coherency*=NULL)• box boundingBox() const• bool intersect(const ray&, intersection&)• float costs(cost_type);

• Implemented• VRML97 input

• Work in progress• subdivision surfaces (view-dependent tesselation)



Dynamic Hierarchy Adaption

static

potentially dynamic

dynamic

optimized graph

optimized graph

list

buffer

optimize thread

update thread

list



Navigation

• Based on ray casting functionality



Conclusions

• Multi-threaded culling framework on static and dynamic environments (optimize, cull, render, update, navigate, intersect, ...)

• Interactive exploration of large models based on optimized scene hierarchies

• Easy to extend (culling, objects, ...)

hierarchical data structures for efficient rendering and navigation

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