Death Stranding created quite a buzz when it was announced at E3 last year. The graphics looked good then, but Hideo Kojima later revealed that his company would be using Guerrilla Games' Decima Engine for the project. Since then, we haven't heard much about the game, but we did get an update on the engine from a SIGGRAPH presentation in Los Angeles this week.
Giliam de Carpentier, principal tech programmer with Guerrilla Games, and Kohei Ishiyama of Kojima Productions held a session on the Decima Engine: Advances in Lighting and AA (via DualShockers), showing of the fog system in the upcoming PS4 exclusive game. The duo explained that Death Stranding needed photo-realistic rendering for the game, and that the engine had to be modified to accommodate that. While the Decima engine is built with that type of rendering in mind, Kojima Productions wanted the ability to show dense or even colored fog, which requires modifications to the engine. The studio had to develop the system independently.
The technical aspects are best understood by engine programmers, but here is a bit on what exactly the engine is doing and how it is accomplished (again via DualShockers):
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.
Two weather types were precomputed, sunny and dense fog. They can be used as a base to express various weather conditions with no further precomputation required.
The videos below offer some visual explanation of the description above.