Creating Accurate Anisotropic Lights with Linear Transformed Cosines

Linearly Transformed Cosines, or LTCs, are a set of tools used for quick and accurate shading in games. They're great because they can be calculated quickly. Right now, game engines use LTCs to mimic a model called GGX, but only in its simplest form called isotropic GGX. When it comes to the more complex anisotropic GGX, things get tricky. The extra dimensions in anisotropic GGX cause problems when trying to fit, process, store, and interpolate LTCs. Each step can lead to issues in the final look. To fix this, we need to be careful with how we handle these steps. By finding patterns in how LTCs behave, we've solved these problems.Now, we have a guide, like a little encyclopedia, that helps us adjust LTCs for anisotropic GGX. This guide is small, only $8^4$ in size, and it lets us make realistic light shading without any visible errors. This brings anisotropic GGX into real-time shading for the first time. Think about it like trying to make a really accurate shadow. If you're working with just one light source, it's easy. But when you add more lights and angles, it gets hard. You need a good guide to make sure everything looks right. That's what this discovery is for LTCs and anisotropic GGX.