Behind the Scenes: Cloth shading (Patreon)

Greetings! Some expressed curiosity in game making under last month's report, so I decided to take some time out to briefly discourse on the dirty work we are currently pulling out in the black box. The technique part can get boring and nerdy, so you can safely ignore this article if not interested.

Many of you may have already heard of the term Physically Based Rendering, which is the fundamental concept behind BRDF or PBR pipeline. With Zbrush, Substance Painter and Designer ascending to the new standard nowadays, it seems that it is never so easy to accomplish a believable visual effect for materials in mainstream engines such as UE4 and Unity. All you need to do is baking a normal map and decide how smooth and metallic the material is, then connect the nodes in visualized shader manager like first-grade matching quiz. A large sum of amateur indie developers (and even a considerable portion of developers of well-known titles) stop here, but this is actually only the first step.

The default PBR shader of UE4 works well under most circumstances, but it's ability is limited when special specularity model is required. The formula I attached is a simplified form of Oren–Nayar reflectance model, derived from which we can implement a dedicated shader to better mimic textiles with multiple layers of reflection, such as silk and satin. In our case, the stockings.

There are two valid approaches to make sure the custom shader reflects the light in the same fashion as real textiles: TAs at Naughty Dog will model the micro fiber structure of the cloth and bake them into a depth map, then apply it as a tiling texture. Square Enix, on the other hand, adopts 3D scanning to analyze material's optical characteristics. By the way, those fancy foods in FFXV were mostly not modeled and colored by hand, but scanned and retopoed.

Lacking both the manpower and equipment, we resort to trail and error. With different combinations of parameters and constant improvements on the texture itself, the outcome will eventually be satisfying enough.