Paper Presentation - Micropolygon Ray Tracing With Defocus and Motion Blur - Qiming Hou, Hao Qin, Wenyao Li, Baining Guo, Kun Zhou Presenter : Jong Hyeob Lee

2 Micropolygon ● What is a micropolygon? Polygon Micropolygon

3 Defocus and Motion Blur

4 Rasterization vs Ray Tracing ● Tracing a ray is slower than rasterizing a pixel. ● Every ray returns something useful. Rasterization waste time on not-covered or occluded pixels. ● Tradeoff between per-operation cost and useful operation percentage. ● Stochastic sampling favors ray tracing.

5 Goal ● A 4D micropolygon ray tracing ● Performs up to an order of magnitude faster than rasterization. ● Eliminates the quality-performance tradeoff in defocus and motion blur rendering.

6 Related Works ● Micropolygon ● Reyes [Cook et al. 1987] ● RenderAnts [Zhou et al. 2009] ● Defocus and Motion Blur ● Adaptive sampling [Hachisuka et al. 2008] ● Hyper-trapezoids ● Collision detection [Hubbard 1995]

7 Overview ● Hyper-trapezoid ● BVH Construction ● Ray Generation ● BVH Traversal

8 Overview ● Hyper-trapezoid ● BVH Construction ● Ray Generation ● BVH Traversal

9 Hyper-trapezoid ● A hyper-trapezoid is… ● Two faces at T=0, T=1 interpolated linearly across T

10 Hyper-trapezoid ● Axis-aligned bound box & Bounding box based hyper-trapezoid

11 Hyper-trapezoid ● 4D OBB hyper-trapezoids ● The T=0 and T=1 faces are 3D OBB, analogous to 3D Hyper-trapezoids with 2D Bouding Box faces. T=0 T=1

12 Comparisons with AABB ● Test scenes (Furball, Ladybug, Fairy, Car)

13 Comparisons with AABB

14 Overview ● Hyper-trapezoid ● BVH Construction ● Ray Generation ● BVH Traversal

15 BVH Construction ● Basic topology is the same as general BVH.

16 BVH Construction ● Build process ● Top level BVH ● In-grid level BVH ● Compute bounding volume

17 BVH Construction ● Top level BVH ● Unit : Micropolygon grid ● Split strategy : Surface Area Heuristic ● Termination criterion : One gird in every node

18 BVH Construction ● In-grid level BVH ● Unit : Micropolygons ● Split strategy : Parametric space mid-split ● Termination criterion : Less than 8 micropolygons in a node

19 BVH Construction ● Compute bounding volume ● Compute grid-level orientation ● Bottom-up merge : use the orientation that results in smaller surface area. ● Top-down simplify : use parent node’s orientation if surface area isn’t increased too much.

20 Overview ● Hyper-trapezoid ● BVH Construction ● Ray Generation ● BVH Traversal

21 Ray Generation ● Reducing the alias ● Lens permutation : magic square ● Time permutation : magic square shuffled and shifted per-pixel

22 Overview ● Hyper-trapezoid ● BVH Construction ● Ray Generation ● BVH Traversal

23 BVH Traversal – Ray and OBB ● Transforming rays into per-box local frame.

24 BVH Traversal – Ray and OBB ● Transforming rays into per-box local frame.

25 BVH Traversal - Micropolygon ● Use a rasterization-like method to compute pseudo-intersections for micropolygons. ● Project micropolygon to view plane. ● Use even-odd rule to test it.

26 Comparison with Rasterization ● Better quality

27 Comparisons with AABB ● Test scenes (Furball, Ladybug, Fairy, Car)

28 Comparison with Rasterization ● Faster sampling time

29 Result – Total rendering time

30 Conclusion ● The first time ray tracing is faster than rasterizaion. ● A novel acceleration structure based on oriented hypertrapezoid. ● Limitation : ● Inefficiency of transparency handling ● The BVH is not effective when tracing rays inside objects over rasterization methods.

31 Q&A ● Thank you.