Interactive Ray Tracing of Dynamic Scenes Tomáš DAVIDOVIČ Czech Technical University

2 Three types of scenes Static scenes Contained movement Explosions…

3 Three types of scenes Related work Havran et al 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 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 Buddha 1M tris A10 218k tris Sibenik’s Cathedral 80k 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 leaf BP – Bouding planes test NF – 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 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 attention Questions? Tomáš DAVIDOVIČ Czech Technical University