Kristóf Ralovich

Budapest University of Technology and Economics

Agenda

• Quick overview of ray tracing• Programmable pipeline• Storing the scene• GPU ray tracing• Results• Future work

Concept of ray tracing

occluder

camera

light

viewport

diffuse objectprimary rayshadow ray

reflectiveobject

reflected ray

Accelerating ray shooting

• uniform grid space subdivision• 3D DDA traversal [Amanatides & Woo]

Pipeline > computing stage

fragment program(kernel)

screen covered byrasterized fragments

fragments torender target(s)

texturememory

draw full screen quad

1 : 1 mapping ofrays to fragments

render targets canbe fed back as textures

programmable pipeline

texture

memory

vertexprocessor

rasterization

fragmentprocessor

render target(on/off-screen)

rendering pass /kernel execution

Scene encoded in textures3D RGB grid texture

ptr cnt proxcld.

R G B030

triID

2D LUMINANCE triangle list texture L

320 000

0 2 3 0 2 4 7 8

...

9 ...2x 3D RGB texturefor triangle data4 sliceseach

x

R

y

G

z

B

x y zx y zr g bx y zx y zx y zrc

...tri0 tri1 tri2 tri3 tri4 tri5 tri6 tri7 triN

v1v2v3coln1n2n3refl

540

vox0 vox1vox2 vox3 voxK

tri listreferencedin vox0

tri listreferencedvox2

GPU ray tracer (ray generation)

scene AABB hit? (masking)and 3D DDA initialization

ray generator

shading

traverse

intersect+

stage output inrender targets:

ray origins ray directions

GPU ray tracer (initialization)

scene AABB hit? (masking)and 3D DDA initialization

ray generator

shading

traverse

intersect+

xyz

xyz

xyz

xyz

xyz

xyz

xyz

xyz

xyz

xyz

xyz

xyz

xyz

xyz

xyz

xyz

3D DDA tMax

xzyfin?xzyfin?

xzyfin?xzyfin?

xzyfin?

xzyfin?xzyfin?

xzyfin?xzyfin?

xzyfin?xzyfin?

xzyfin?xzyfin?

xzyfin?xzyfin?

xzyfin?

curr. voxel +finished? flag

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

hit record:barycentric u,v +ray param. t +triID

stage output inrender targets:

GPU ray tracer (trav. + isec. 1)

scene AABB hit? (masking)and 3D DDA initialization

ray generator

shading

traverse

intersect+

xzy#trisxzy#tris

xzy#trisxzy#tris

xzy#trisxzy#tris

xzy#trisxzy#tris

xzy#trisxzy#tris

xzy#trisxzy#tris

xzy#trisxzy#tris

xzy#trisxzy#tris

3D DDA tMax +# of proc. tris

xzyfin?xzyfin?

xzyfin?xzyfin?

xzyfin?

xzyfin?xzyfin?

xzyfin?xzyfin?

xzyfin?xzyfin?

xzyfin?xzyfin?

xzyfin?xzyfin?

xzyfin?

curr. voxel +finished? flag

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

hit record:barycentric u,v +ray param. t +triID

stage output inrender targets:

pass repeated until all ray are finished(halting cond. det. by occlusion query)

GPU ray tracer (trav. + isec. 2)

scene AABB hit? (masking)and 3D DDA initialization

ray generator

shading

traverse

intersect+

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

hit record:barycentric u,v +ray param. t +triID

stage output inrender targets:

GPU ray tracer (shading)

scene AABB hit? (masking)and 3D DDA initialization

ray generator

shading

traverse

intersect+

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

uvtID

hit record:barycentric u,v +ray param. t +triID

accumulatedcolorvalues

stage output inrender targets:

Evaluated scenes

Knight Torus Knot Bunny (low poly) Stanford Bunny

14x16x14 grid

636 tris

16x16x16 grid

1024 tris

20x20x20 grid

1764 tris

128x128x128 grid

69451 tris

2.6 - 9.7 FPS 1.5 - 8.4 FPS 3.3 - 11.6 FPS 0.8 - 3.0 FPS

Experiences: Lessons learned

Pros.

ray tracing and GPU are both paralell uniform grid traversal is fast and simple

Cons

abstraction over graphics APIno stack for recursiongrid is not adaptive

Future

• SM 4.0 GPU: integer arith, geom. feedback

• others RASs on GPU: KD-tree [Foley & Sugerman 2005], BVH [Thrane & Simonsen 2005], geometry images [Carr et. al. 2006]

• better API to HW: CUDA• different HW: Cell

Thank you for yourattention!

• Questions?