Death Stranding’s Impressive Fog System Revealed by Kojima Productions. Kojima Productions introduces the advanced height fog system being created for Death Stranding within the Decima Engine.

During a presentation at Siggraph 2017 in Los Angeles, Gerrilla Games Principal Tech Programmer Giliam de Carpentier and Kojima Productions’ Kohei Ishiyama hosted a presentation titled Decima Engine: Advances in Lighting and AAproviding a look into the fog system that is being developed for Death Stranding.

Decima Engine has a flexible atmospheric scattering system linked with clouds and outdoor lighting, but Kojima Productions needed a system optimized for photo-realistic rendering.

Normally precomputed atmospheric scattering is one of the best methods for photo-realistic games. It works well to create a photo-realistic atmosphere, but developers often need to express artistic quantities like dense fog and colored fog in the actual game.

Instead, it would be advantageous to be able to express the photo-realistic aerial perspective (which is a technique that creates an illusion of depth by representing more distant objects as fainter and more blue) and the artistic height fog with a single height fog model. In order to achieve this result, the developer created an analytic height fog model combined with a precomputed atmospheric scattering model.

While the precomputed atmospheric scattering model performs numerical integration, storing the in-scattering and transmittance information into Look-Up-Tables (LUT), the height fog model  calculates the fog directly when the scene is rendered.

Since Kojima Productions couldn’t find a satisfactory analytic solution for the height fog model, they developed it independently. In Kojima Production’s approach information about the sun like and the sky light us supplied to the height fog model from the precomputed atmospheric scattering model.

In sunlight conditions, the light is incident to the ground, and interacts with the atmosphere. The precomputed model generates the scattering information and stores it in the LUT. The height fog model then receives info in background radiation, sunlight and skylight from the precomputed model.

While the precomputed atmospheric scattering model used is nothing special, the LUT used is different from the typical model. The implementation used by Kojima Productions mainly uses Bruneton’s and Elek’s model with some optimizations.

Normally a precomputed atmospheric scattering model has in-scatter and transmittance LUTs, but Kojima Productions replaced the transmittance LUT with sunlight and skylight LUTs, because they want to feed the information for sunlight and skylight directly into the analytic height fog model.

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