Virtual Light Field Groupvlfproject@cs.ucl.ac.ukUniversity College London

GR/R13685/01

Research funded by:

Ray Tracing Dynamic Scenes with VLF-RT

Pankaj Khanna

p.khanna@cs.ucl.ac.uk

VLF Project

Dynamics in a scene

Structured motion– Animation of all polygons

in dynamic object can be expressed by a single transformation matrix

Unstructured motion– Polygons of dynamic

object undergo unrelated transformations

BART Museum7 Scene: Jonas Lext, Ulf Assarsson, and Tomas Akenine-Möller, ``A Benchmark for Animated Ray Tracing'', IEEE Computer Graphics and Applications, pp. 22-31, March/April 2001. http://fibbla.ce.chalmers.se/BART/

VLF Project

Changes to the VLF-RT data-structure

Each tile now has a linear list of dynamic polygons that overlap it– Currently a fixed-size array allocated on demand

Global frame-counter and local update-frame counter mechanism to track validity & updates

VLF Project

Updating tiles on an animation change

Rasterization of dynamic polygons (in tile-space) at float-precision

– Problems with integer-arithmetic rasterization– CPU vs GPU rasterization– Set tile’s update-frame counter to global counter– Multithreaded (1/2 PSFs each)

VLF Project

On-demand tile updating

Updating a PSF’s tiles is only important if rays are to be tested along that PSF

Update a PSF on-demand if a ray is to be tested for intersection along it

– Implicitly multi-threaded (as ray-tracing is multi-threaded)– Locking of updates (critical section)

Minimize locking by interleaved traversal of screen rows in top-down & bottom-up orders

– Significant speed-up for Simple (false-colour) & OpenGL shading, marginal (or possibly negative) for Whitted

VLF Project

Ray-intersection test

First intersect static scene using Tile-BSP scheme discussed earlier (for static VLF-RT)

Then intersect linear list of dynamic polygons in the corresponding tile– Alternative scheme to do dynamic first & then

static could significantly reduce intersection-test time

VLF Project

Intersecting dynamic polygons

Structured motion– Can use pre-processed information to use faster

intersection kernel Wald, I, “Realtime Ray Tracing and Interactive Global Illumination”, PhD Thesis,

2004

Unstructured motion– Pre-processing not possible as polygons change

shape/size/orientation per-frame– Currently using (slower) Möller-Trumbore intersection test

Tomas Möller and Ben Trumbore, “Fast, Minimum Storage Ray-Triangle Intersection”, Journal of Graphics Tools, Vol. 2, No. 1, pp. 21-28 1997.

VLF Project

Results

Structured Motion– Video/Demo

207 static & 564 dynamic polygons, 1 emitter

(32x32 Tiling, On-Demand PSF updates)

Simple ‘OpenGL’ Whitted

Total 9.611 10.862 40.559

Min 0.126 0.143 0.521

Max 0.139 0.166 0.617

Avg 0.129 0.146 0.548

StdDev 0.002 0.003 0.022

VLF Project

Results

Unstructured Motion– BART Video

BART museum7 scene

10,284 static polygons

16,384 dynamic polygons

2 point-emitters

Total: 3,867.66 seconds

Max: 38.88 seconds

Average: 12.89 seconds

StdDev.: 8.1543

Tiling: 64x64

Tile-BSP Depth: 6

(Offline Rendered on Dual 2.8Ghz Xeon, 3GB RAM)

VLF Project

Limitations & Future-work

Currently dynamic objects must remain within confines of static scene

Currently polygons (triangles) only– Other primitives are possible if a fast 2D rasterisation &

intersection can be performed

Alternate approach to represent structured dynamic object in its own VLF-RT space (with associated directions) so that coarse tile-updates will suffice

VLF Project

Related publications

Khanna, P., Mortensen, J., Yu, I., Slater, M. (2004) A Visibility Field for Dynamic Ray Tracing, Technical Report, University College London

Khanna, P., Mortensen, J., Yu, I., Slater, M. (2004) Fast Ray Tracing of Scenes with Unstructured Motion, Technical Report, University College London

For these and other related work, see: http://www.cs.ucl.ac.uk/research/vr/Projects/VLF/Media/