Volumetric participating media can significantly impact the realism of virtual scenes, due to both the subtle interplay between surface-and volume-transport effects and the presence of entities like smoke and clouds. Modern video games increasingly seek to include such effects to improve realism and artistic flexibility. While many works propose efficient simulation methods for volumetric single- and multiple-scattering (e.g., [Hil15; Wro14]), no interactive methods accurately model the effects of scattering from a volume onto other surfaces/locations in a scene, let alone several such bounces. Volume-to-surface transport has been studied in offline image synthesis but these methods are too costly for interactive content pipeline. We propose a very efficient method to include the neglected volume-to-surface interactions during precomputation, resulting in more accurate lighting with only modest performance overhead. Instead of relying on costly volumetric light transport simulation, we model the spherical impulse response of volumetric light in a form that allows us to quickly precompute volume-to-surface transport.
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