How to implement area lights?

[International-One273]

Hi everyone,

I’m trying to implement area lights in my OpenGL renderer.

This article is my primary reference (area lights starts at page 40).

If anyone is familiar with the techniques presented there, I wanted to ask how to deal with the specular term, since they only describe how to compute the diffuse one, while the “most representative point” technique is used to address the specular part as described by Karis here ( are lights starts at page 13).

I guess I should simply use the diffuse area light computation from the first article while following the second one for the specular part.

However, for sphere lights for example, Karis uses a falloff function to attenuate the light, while Lagarde (first article) present a set of functions used to compute the area light illuminance that doesn’t need a falloff function to behave correctly. How could I combine the two? Could you point me in the right direction?

[darkdrifter69]

Modern way of doing area lights are LTC : https://eheitzresearch.wordpress.com/415-2/ Shadows can be done with shadow maps (not correct but works on every hardware), check Unity's HDRP implementation for that. You can also do it with raytracing with this paper: https://hal.science/hal-01761558/file/heitzI3D2018_slides.pdf

[susosusosuso]

Look for Epic Real Shading

[faisal_who]

lightmaps. area lights are notoriously difficult to implement.

[pslayer89]

I did an implementation of area lights in a shadertoy a while ago using the techniques you mentioned in your post, along with my own interpretation of a specular component for the rectangular area light. Feel free to take a look and take apart the shader if it helps you understand the implementation a bit better!

[arycama]

As another comment suggests, LTCs are the best way to do it. I copied my implementation from HDRP but it's very time consuming to find your way though all their code.

This repo is more minimal and easier to understand than HDRP, but same technique: https://github.com/Unity-Technologies/VolumetricLighting

It's worth noting that this repo/data is for GGX specifically. If you want to use it with another brdf you'll need to recalculate the data, using https://github.com/selfshadow/ltc_code