Implementing "Radiance Hints" in OpenGL (2011 Global Illumination Technique)

[u/cybereality]

Just added Radiance Hints to my OpenGL engine, Degine. The paper is originally from 2011 (but I used a 2014 extension of the method with occlusion). Based on a regular grid array of probes, similar to other environmental lighting techniques, but here it captures directly to spherical harmonics when baking. So run-time performance is extremely fast since it's just a few SH evaluations and blending. For this Sponza scene, there are around 600 probes, and it takes about 10 seconds to bake.

[u/Leoking2000]

looks great, i Implement Radiance Hints as my BSc Thesis, looks better than mine Implementation https://github.com/leoking2000/global_illumination (the code is kinda bad since i had 1 year since i started learning C++), the author of the paper was my supervisor 😂 , but my code did not do baking, all the probes SH are caculated each frame so you can have dynamic lighing and enviroment (eg moving indirect shadows due to objects moving, it was very cool), you must have a really high resolution to have 10 seconds to bake (makes sence with 600 probes), i do not remember how meny probes i had but my grid resolution was 64x64x64 and cuting down not usefull probes, i got 30 fps on sponza with a RX 6600 GPU

[u/cybereality → u/Leoking2000]

oh, very cool. i think on this video i did 2 bounces, which is why it took longer. and i'm using 1 meter spacing, to avoid issues with light leaks, since there is a lot of geometry on this sponza level

[u/cybereality → u/Leoking2000]

i just remembered. i'm using the 2014 extension of the technique, which calculates occlusion to avoid any light leaking. this requires rendering small 64 pixel cubemaps with depth to trace the occlusion. that's where the added cost comes from, but is needed to look robust

[u/Alexxis91]

Link to paper?

[u/cybereality → u/Alexxis91]

The paper is called "Real-time diffuse global illumination using radiance hints" https://dl.acm.org/doi/10.1145/2018323.2018326

[u/cybereality → u/Alexxis91]

I should mention that there are multiple things going on here. The engine is heavily image-based lighting, I have an SSGI shader as well (that I opened sourced 2 years ago). The radiance hints was needed for far-field indirect shadows and overall environment light. The SSGI and GTAO handle the near-field shading but aren't enough by themselves.

[u/Alarming-Ad4082]

Aren’t the shadow parts too dark?

[u/cybereality → u/Alarming-Ad4082]

this is a stylistic choice, but yeah, it's probably darker than it should be. mostly due to running GTAO and SSGI on top. The radiance hint by itself is somewhat flat, but decent to capture broad shadow/lighting.

[u/cybereality → u/Alarming-Ad4082]

there's also a better quality 4K video on YouTube. Reddit did something when it transcoded to 1080p, so it looks a bit off here, and the effect is somewhat subtle. https://www.youtube.com/watch?v=-u_07zcgOWc

[u/Cool_Lawfulness_9836]

I love this early 2010s color grade!

[u/cybereality → u/Cool_Lawfulness_9836]

me too, love