The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

Soft Shadows using Hardware Cameras

Kyle MooreCOMP 870

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Previous Work

• Cone Tracing ♦ Amanatides, J. 1984. Ray tracing with

cones. In Proceedings of the 11th Annual Conference on Computer Graphics and interactive Techniques H. Christiansen, Ed. SIGGRAPH '84. ACM Press, New York, NY, 129-135.

♦ Uses cones shaped rays instead of lines to calculate light intersections with objects

♦ Lots of difficult computations

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Previous Work

• Forward Hardware-Based Techniques♦ Assarsson, U. and Akenine-Möller, T. 2003. A

geometry-based soft shadow volume algorithm using graphics hardware. ACM Trans. Graph. 22, 3 (Jul. 2003), 511-520.

♦ Uses silhouette edges to case penumbra volumes which are to create shadow maps

♦ This is an approximation and can be inaccurate

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Previous Work

• Backwards silhouette edge detection♦ Laine, S., Aila, T., Assarsson, U., Lehtinen, J.,

and Akenine-Möller, T. 2005. Soft shadow volumes for ray tracing. ACM Trans. Graph. 24, 3 (Jul. 2005), 1156-1165.

♦ Uses a hemicube acceleration structure to find silhouette edges to calculate the amount of light occlusion

♦ Doesn’t take advantage of hardware

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My idea

• My Inspiration♦ While working on my ray tracer♦ Unhappy with soft shadows♦ Wanted to shoot more rays, but high cost

• New approach♦ Let graphics hardware simulate shooting

many rays♦ Perhaps get performance increase as well

as quality enhancement

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My Approach

Area Light Source

Occluder

Surface

Hardware Camera

View Frustum

Camera’s ViewAverage Pixels to getOcclusion percentage

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My Approach

Area Light Source

Occluder

Surface

Camera’s View

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My Application

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Results - Quality

Old approach 4x4 grid My Approach 4x4 grid

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Results - Quality

Old approach 17x17 grid My Approach 17x17 grid

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Results - Performance

Old approach 17x17 grid152 seconds

My Approach 32x32 grid96 seconds

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Performance

Rays Camera naive

Camera w/ small optimizations

4x4 42 secs 151 secs

17x17 152 secs 158 secs

32x32 447 secs 160 secs 96 secs

64x64 181 secs

128x128 241 secs

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Room for improvement

• Each pixel draws a frame and the fetches the results

• Feedback loops are slow in hardware

• Does not take advantage of parallelization of using CPU and GPU at the same time