1

Rendering Transitions in a Geometric Level of Detail Framework

Defended by Shaun David Ramsey

On July 27, 2004

2/41

Outline

Motivation - Hierarchy of Structure Contributions

Arbitrary Polyhedral Simplification Structure Combination Ray Tracing Techniques

Results

3/41

Video Generation

Large amount of detail dependent on viewing angle, and viewing location

4/41

Rendering Structure

Macro Meso Micro

5/41

Geometry

Mesh Sizes continue to grow Varied Representations

6/41

Simplification

7/41

Level of Detail Hierarchies

8/41

Progressive Meshes

Level Of Detail Hierarchy Edge Collapse Texture Mapping

9/41

What’s Missing?

Mesostructure Displacement maps Bump maps

Microstructure BRDFs

Algorithms to utilize Rendering Methods

10/41

What’s Missing? BRDFs

11/41

What’s Missing? Bump Maps

12/41

What’s Missing? Displacement Maps

13/41

What’s Missing? Rendering Transitions

Construct BRDFs, bump maps and displacement maps with consistent intensities

Redistributed bump mapping algorithm

Becker and Max 1993

14/41

Spanning the Gap

Combine simplifications for meso-, micro- and macrostructure

Incorporate view-dependent rendering techniques in a geometric level of detail framework.

15/41

Outline

Motivation - Hierarchy of Structure

Contributions Arbitrary Polyhedral Simplification Structure Combination Ray Tracing Techniques

Results

16/41

Arbitrary Polyhedral Simplification

Edge collapses for arbitrary polyhedra Ramsey, Bertram, and Hansen [CGIM 2003]

17/41

Normal Deviation

Use normal deviation to drive simplification Complicated records for APS

18/41

Changing Thresholds

Original Simplified Simplified21590 polys 5600 polys 5600 polys

cos=0.95 cos=0.0

19/41

Outline

Motivation - Hierarchy of Structure Contributions

Arbitrary Polyhedral Simplification Structure Combination (Rendering+LOD) Ray Tracing Techniques (BPs, Disp PMs)

Results

20/41

Structure Combination

Rendering System required to glue pieces together Ray Tracing Bilinear Patches for Normal

Distributions (BRDFs, RBM) Ray Tracing Displaced Progressive Meshes

(Combines LOD with Appearance)

21/41

Rendering Transitions

Becker [1992] and Becker and Max [1993] Construct BRDFs and RBMs from normal

distributions Transition between BRDFs, RBMs

(interpolation) and between RBMs and displacement maps (partial bumps)

22/41

Construct Normal Distributions

Ray Trace displaced plane with scalar height field (why not use bilinear patches)

23/41

Bilinear Patches

Eliminate Bias

24/41

Ray Tracing Bilinear Patches

Bilinear Patches [Ramsey, Potter, Hansen JGT 2004]

P(t) = r + t q P(u,v) = (1-u)(1-v) p00 + (1-u)v p01

+ u(1-v) p10 + uv p11

= a uv + b u + c v + d Solve P(u,v) = P(t)

25/41

Quadratics

Reduce numerical error and instability

26/41

Efficiency

790m intersection tests Ray-Bilinear Patches 754s (1.05m tests/s) Two Plane-Bilinear Patches 963s (0.82m tests/s)

27/41

Ray Traced PMs with Rendering Transitions

General Algorithm with Discrete LOD Determine LOD Li to use (d)

Ray Trace Li

Determine Rendering Method (d, ) If Displaced or Partial Bump, ray trace

Else compute intensity from BRDF and RBM

28/41

Negative Displacements

d

-d

29/41

Transitioned Displacements

Partial bumps with negative displacements

30/41

Ray Tracing Displacements

Many levels of 4-to-1 subdivision Pass proportion to each triangle

31/41

Contributions

Arbitrary Polyhedral Simplification Rendering (Ray Tracing):

Bilinear Patch Intersections Displaced Progressive Meshes Rendering Transitions

Combining Rendering Transitions in a Geometric Level of Detail Framework

32/41

Outline

Motivation - Hierarchy of Structure Contributions

Arbitrary Polyhedral Simplification Structure Combination Ray Tracing Techniques

Results

33/41

Effect of Subdivision Level

l=1, *4 l=2, *16 l=3, *64

l=4,*256 l=5, *1024 l describes subdivision level, * describes triangles rendered per original triangle in the model

34/41

Results - transitions

Disp are greenBumps are blueBRDFs are red

35/41

Results – changing LOD

4500 polys 3500 polys 3500 polys 2500 polys

2500 polys 1500 polys 1500 polys 500 polys

36/41

Results – user params

Change transitions, change PMs, heights

Disp are green Bumps are blue BRDFs are red

37/41

Results - Movies

Displaced Movie - Scintillation Color Movie – when transitions are used Rendered Movie – the full LOD/transition

system

38/41

Rendering Times

Rendering Method

Mesh 0.33s 0.11s 0.38s

BRDF 0.40s 0.11s 0.45s

RBM 3.70s 1.40s 3.99s

Displaced Detailed 24.95s 5.09s 41.52s

LOD Transition System 3.70s 1.33s 31.28s

39/41

Future Work

Shadows Displacement map rendering Distributed Ray Tracing

40/41

Other Rendering Techniques

Realistic Materials Subsurface scattering BRDFs (anisotropy, specularity)

Replace the BRDF with Bitextures Hardware (VDMs)

41/41

The End

•Questions?