LogInIt is calculated anew for each frame.
Take a look at this beautiful celebration of color. The light in the video above moves in a certain, realistic way thanks to a new approach described by Alexander Sannikov, a Senior Programmer at Grinding Gear Games – the developer behind Path of Exile.
Sannikov presented a novel data structure called radiance cascades, which allows for effectively storing and calculating a radiance field by decomposing it into multiple ranges and storing them separately.
Image credit: Asbjørn Lystrup
According to his paper, radiance cascades are based on the idea that "in order to resolve radiance emitted by an object, one needs to have higher linear resolution next to it and higher angular resolution farther away from it."
Image credit: Asbjørn Lystrup
"Radiance cascades exhibit a distinctly unique way of asymptotic scaling that for all practical purposes is equivalent to casting infinitely many rays in a finite amount of time while using a finite amount of memory."
Image credit: Alexander Sannikov
Sannikov also points out that radiance cascades are completely geometry-agnostic; "they encode radiance at a constant cost that is independent of scene complexity, number of light sources or polygons present in the scene." He says that the cascades are scene-independent and calculate lighting for 2, 102, and 1002 particles in the same amount of time of about 12ms.
This approach should remove the rays as the primary constraint for calculating global illumination, resulting in natural-looking, quickly processed lighting that works effectively within memory limitations.
The video at the beginning of the article, provided by Asbjørn Lystrup, demonstrates how this setup can run at 0.3ms per frame on the GTX 970 with no denoising or temporal accumulation. Radiance fields are built from scratch every frame without reusing any data from the previous frame.
Image credit: Alexander Sannikov
Sannikov's paper is still in development, but if you want to learn all the technical details, read the paper here. The author has also talked about rendering in Path of Exile, check it out if you're interested in his work:
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