Paper Presentation- Micropolygon Ray Tracing With Defocus and Motion Blur -

Qiming Hou, Hao Qin, Wenyao Li, Baining Guo, Kun Zhou

Presenter : Jong Hyeob Lee

2010. 10. 28

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Micropolygon

● What is a micropolygon?

Polygon Micropolygon

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Defocus and Motion Blur

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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.

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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.

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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]

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Overview

● Hyper-trapezoid

● BVH Construction

● Ray Generation

● BVH Traversal

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Overview

● Hyper-trapezoid

● BVH Construction

● Ray Generation

● BVH Traversal

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Hyper-trapezoid

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

linearly across T

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Hyper-trapezoid

● Axis-aligned bound box & Bounding box based hyper-

trapezoid

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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=0T=1

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Comparisons with AABB

● Test scenes (Furball, Ladybug, Fairy, Car)

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Comparisons with AABB

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Overview

● Hyper-trapezoid

● BVH Construction

● Ray Generation

● BVH Traversal

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BVH Construction

● Basic topology is the same as general BVH.

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BVH Construction

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

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BVH Construction

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

node

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BVH Construction

● In-grid level BVH● Unit : Micropolygons● Split strategy : Parametric space mid-split● Termination criterion : Less than 8

micropolygons in a node

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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.

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Overview

● Hyper-trapezoid

● BVH Construction

● Ray Generation

● BVH Traversal

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Ray Generation

● Reducing the alias● Lens permutation : magic square● Time permutation : magic square shuffled

and shifted per-pixel

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Overview

● Hyper-trapezoid

● BVH Construction

● Ray Generation

● BVH Traversal

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BVH Traversal – Ray and OBB

● Transforming rays into per-box local frame.

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BVH Traversal – Ray and OBB

● Transforming rays into per-box local frame.

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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.

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Comparison with Rasterization

● Better quality

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Comparisons with AABB

● Test scenes (Furball, Ladybug, Fairy, Car)

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Comparison with Rasterization

● Faster sampling time

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Result – Total rendering time

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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.

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Q&A

● Thank you.