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Realizing Multi-Hit Ray Tracing in Embree & OSPRay Christiaan Gribble SURVICE Engineering Intel HPC Developer Conference 12 November 2016 Take-home messages Multi-hit ray traversal Enables a new class of ray-based rendering &

  1. Realizing Multi-Hit Ray Tracing in Embree & OSPRay Christiaan Gribble SURVICE Engineering Intel HPC Developer Conference 12 November 2016

  2. Take-home messages • Multi-hit ray traversal Enables a new class of ray-based rendering & simulation applications • Embree permits efficient implementation • OSPRay permits easy integration 2 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  3. Take-home messages • Multi-hit ray traversal • Embree permits efficient implementation Intersection filter functions enable user-level implementation of state-of-the-art multi-hit ray traversal techniques • OSPRay permits easy integration 3 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  4. Take-home messages • Multi-hit ray traversal • Embree permits efficient implementation • OSPRay permits easy integration Supports scalable, high performance visual analysis tools across optical & non-optical domains 4 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  5. Acknowledgements • SURVICE • Joe Rosenthal • Mark Butkiewicz • Intel • Jeff Amstutz • Ingo Wald • Jim Jeffers 5 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  6. Overview

  7. Interval computation Optical rendering 7 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  8. Interval computation Optical rendering 8 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  9. Interval computation Optical rendering Non-optical rendering 9 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  10. Interval computation Optical rendering Non-optical rendering 10 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  11. Interval computation Non-optical rendering 11 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  12. Interval computation Non-optical rendering 12 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  13. Interval computation Non-optical rendering Interval computation 13 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  14. Interval computation • Difficult or impossible • Epsilon hacks • Missed/repeated intersections • Performance impacts 14 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  15. Interval computation • Difficult or impossible • Performance impacts • Traversal restart • Operational overhead 15 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  16. Interval computation • Difficult or impossible • Performance impacts Is there a better solution? 16 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  17. Multi-hit ray traversal • Which primitives are intersected? • One or more, & possibly all • Ordered by t -value along ray • Possible applications • GNK14 • AGGW15 • Gri16, GWA16 17 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  18. Multi-hit ray traversal • Which primitives are intersected? • Possible applications • Transparent rendering • Alpha textures • GNK14 • AGGW15 • Gri16, GWA16 18 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  19. Multi-hit ray traversal • Which primitives are intersected? • Possible applications • GNK14 • Spatial partitioning • Two algorithms: naive, buffered • AGGW15 • Gri16, GWA16 19 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  20. Multi-hit ray traversal • Which primitives are intersected? • Possible applications • GNK14 • AGGW15 • Object partitioning • User-level implementation mechanisms • Gri16, GWA16 20 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  21. Multi-hit ray traversal • Which primitives are intersected? • Possible applications • GNK14 • AGGW15 • Gri16, GWA16 • Enable early-exit in BVH • Implement in Embree & OSPRay 21 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  22. Implementation

  23. Mechanisms • Direct implementation • Kernels specific to multi-hit • Runs counter to our goal • Intersection callbacks • Traversal callbacks • Reference implementation 23 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  24. Mechanisms • Direct implementation • Intersection callbacks • Invoked on valid ray/primitive intersection • User accepts/rejects hit • Traversal callbacks • Reference implementation 24 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  25. Mechanisms • Direct implementation • Intersection callbacks • Traversal callbacks • Invoked on ray/node interaction • Two variants: every-node, leaf-node • Reference implementation 25 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  26. Mechanisms • Direct implementation • Intersection callbacks • Traversal callbacks • Reference implementation • Supports callback mechanisms • Opts for clarity & simplicity http://www.rtvtk.org/~cgribble/research/mhBVH/ 26 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  27. Embree implementation • Intersection filters • Compatible with mainline developments • v2.10.0+ – enables node-culling • Assumptions • Full source code available 27 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  28. Embree implementation • Intersection filters • Assumptions • Nquery known a priori • Preallocated hit data buffer • Initial value beyond range • Full source code available 28 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  29. Embree implementation • Intersection filters • Assumptions • Full source code available • Apache License, v2.0 • Public git repository http://www.rtvtk.org/~cgribble/research/ospMultiHit/ 29 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  30. Scalar implementation static void collectIntersectionsFilter(void* /* unused */, RTCRay& _ray) { 0 // Find index at which to store candidate intersection 1 uint idx = Nquery; 2 while (idx > 0 && ray.tfar < hits[idx-1].tval) 3 { 4 hits[idx] = hits[idx-1]; 5 --idx; 6 } 30 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  31. Scalar implementation 7 // Store intersection, possibly beyond index of the 8 // N ≤ Nquery closest intersections (i.e., at 9 // idx = Nquery) 10 HitData& hit = hits[idx]; 11 hit.geomID = ray.geomID; 12 hit.primID = ray.primID; 13 hit.tval = ray.tfar; 14 hit.Ng = ray.Ng; 15 16 // Update number of intersections identified so far 17 ray.nhits += (ray.nhits < Nquery ? 1 : 0); 31 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  32. Scalar implementation 17 if (ray.nhits < Nquery) 18 { 19 // Reject intersection to continue traversal with 20 // incoming ray interval, as in previous work 21 // [Amstutz et al. 2015] 22 ray.geomID = RTC_INVALID_GEOMETRY_ID; 23 return; 24 } 32 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  33. Scalar implementation 25 // Induce node culling 26 // Trick: set ray.tfar to farthest value among the 27 // N = Nquery intersections identified so far 28 // and (implicitly) accept intersection with 29 // modified ray interval 30 ray.tfar = hits[Nquery-1].tval; 31 } 33 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  34. Results

  35. Performance – tests • Find-first-intersection • First-hit v. multi-hit variants • Isolates multi-hit overhead • Find-all-intersections • Find-some-intersections 35 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  36. Performance – tests • Find-first-intersection • Find-all-intersections • Naive v. node culling multi-hit • Bounds performance expectations • Find-some-intersections 36 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  37. Performance – tests • Find-first-intersection • Find-all-intersections • Find-some-intersections • Naive v. node culling multi-hit • Demonstrates in situ performance 37 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  38. Performance – scenes sibe fair conf truck 80K tris 174K tris 282K tris 426K tris tank hball sanm pplant 1.0M tris 2.8M tris 10.5M tris 12.7M tris 38 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  39. Performance – truck scene 140.0 120.0 +1.08x 0.96x 0.97x 100.0 +1.64x 80.0 60.0 40.0 +4.60x 20.0 0.0 1 10% 30% 70% all Mhps naive culling 39 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  40. Performance – truck scene 140.0 120.0 +1.08x 0.96x 0.97x 100.0 +1.64x 80.0 60.0 40.0 +4.60x 20.0 0.0 1 10% 30% 70% all Mhps naive culling 40 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

  41. Performance – truck scene 140.0 120.0 +1.08x 0.96x 0.97x 100.0 +1.64x 80.0 60.0 40.0 +4.60x 20.0 0.0 1 10% 30% 70% all Mhps naive culling 41 C. Gribble, Realizing Multi-Hit Ray Tracing in Embree & OSPRay

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