Impulse responses for precomputing light from volumetric media

In Proceedings of the Eurographics Symposium on Rendering (EGSR), 2019

In-game screenshot (a) with complex surface and volume shading. Standard lightmaps (d) ignore volume-to-surface transport, while directly-attenuated volume-to-surface illumination (b) captures media shadowing only. Our method (c) additionally capture volumetric single- and multiple-scattered light from emitters and surfaces (e).

Abstract

Modern interactive rendering can rely heavily on precomputed static lighting on surfaces and in volumes. Scattering from volumetric media can be similarly treated using precomputation, but transport from volumes onto surfaces is typically ignored here. We propose a compact, efficient method to simulate volume-to-surface transport during lighting precomputation . We leverage a novel model of the spherical impulse response of light scattered (and attenuated) in volumetric media to simulate light transport from volumes onto surfaces with simple precomputed lookup tables. These tables model the impulse response as a function of distance and angle to the light and surfaces. We then remap the impulse responses to media with arbitrary, potentially heterogeneous scattering parameters and various phase functions. Moreover, we can compose our impulse response model to treat multiple scattering events in the volume (arriving at surfaces). We apply our method to precomputed volume-to-surface light transport in complex scenes, generating results indistinguishable from ground truth simulations. Our tables allow us to precompute volume-to-surface transport orders of magnitude faster than even an optimized path tracing-based solution would.

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Acknowledgements

We thank the anonymous reviewers for their suggestions on improving our exposition, as well as Michal Drobot, Michał Iwanicki, Kyle McKisic and Ari Silvennoinen for insightful discussions. We thank Wenzel Jakob for the Mitsuba renderer [Jak13] we extended to generate the images in Figs. 8 and 9, as well as blendswap.com artist Wig42 and Benedikt Bitterli for the staircase scene in Fig. 8. This work was supported by funding from Activision and an NSERC Discovery Grant (RGPIN-2018-05669).

Cite

@inproceedings{dubouchet19impulse,
    author    = {Dubouchet, Adrien and Sloan, Peter-Pike and Jarosz, Wojciech and Nowrouzezahrai, Derek},
    title     = {Impulse responses for precomputing light from volumetric media},
    booktitle = {Proceedings of the Eurographics Symposium on Rendering (EGSR)},
    year      = {2019},
    month     = jul,
    doi       = {10/gf6rx8},
    publisher = {The Eurographics Association}
}

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