Interactive Ray Tracing of Dynamic Scenes

Tomáš DAVIDOVIČCzech Technical University

2

Three types of scenes

Static scenes Contained movement Explosions…

3

Three types of scenes

Related work Havran et al.

2001 Etc????

Static scenes Build acceleration structure once Trace the structure many times

4

Three types of scenes

Contained movement Build structure once Alter structure when

necessary Trace many times

Related work: Wald et al. 2007

5

Three types of scenes

Explosions… Objects appear, disappear, move

wildly Cannot alter structures

Solution Rebuild every frame Use only once

References Wald et al. 2007

6

What do we need?

Optimize Build + Trace time! Good structure – slow build, fast trace Poor structure – fast build, slow trace Need to find the balance

Fast build of acceleration structure Fast traversal Fast intersection Fast shading

7

What do we need?

Optimize Build + Trace time! Fast build of acceleration structure

Bounding Volume Hierarchy Surface Area Heuristic approx. [Wald et

al.???] Fast traversal

Packet tracing [Wald et al. ????] Fast intersection

Vertex culling [Reshetov et al. ????] Fast shading

8

BVH – SAH cost ratio

Influences: Depth of tree Triangles per

leaf

CTCI

Cost TraversalCostIntersect

Ratio = 0.1~30 tris per leaf

Depth ~20

Ratio = 1.0~3 tris per leaf

Depth ~30

9

Packet traversal

Packets of rays (16x16) Uses SIMD

Traverse the tree Early hit Early miss

When in leaf Intersect triangles

10

Intersection – Vertex Culling

Packet - triangle Beam plane test Triangle edge

test

11

Intersection – Vertex Culling

Packet - triangle Beam plane test Triangle edge

test Standard ray-tri

test

12

Packet shading

For all rays store: Hit point, view direction, normal,

material Go through all hit materials

Store Phong model coefficients Shoot light packets from light to hit

points

13

Packet shading

For all rays store: Hit point, view direction, normal,

material Go through all hit materials

Store Phong model coefficients Shoot light packets from light to hit

points Compute Phong shading for the packet

Using SIMD Add color to the picture

14

Models – no shading

Happy Buddha1M tris

A10218k tris

Sibenik’s Cathedral80k tris

15

Ray tracing performance

less triangles

Primary rays, packets 16x16, resolution 512x512

16

Build + trace performance

less triangles

Primary rays, packets 16x16, resolution 512x512

17

Vertex culling speedup

Many combinations tested; packets 16x16

AB – only rays that hit leafBP – Bouding planes testNF – Triangle edge and Near Far test

18

Shading “speedup”

Packets 16x16, direct illumination, no textures

19

Summary and future work

Can reach 4fps for 200k tris Optimal leaf sizes

2-4 tris per leaf for Trace optimal 20-40 tris per leaf for Build + Trace

optimal Combine acceleration structures

Dynamic and static parts separated Try different acceleration structures

BIH reported to be 2.5x faster (build)

Thank you for attentionQuestions?

Tomáš DAVIDOVIČCzech Technical University