!til &learningjam2024
Just finished processing this paper. I found it very informative but also hard to follow since the math notation made the equations look the same. My notes are basically a condensed version of the whole text, including all the 131 equations of which I'll review and color code the variables.
https://jcgt.org/published/0003/02/03/paper.pdf

&learningjam2024
Recently finished reading through the paper [PM] I mentioned in my last post. It certainly clarified some things and my summary has some inaccuracies in it.
Until I get around to address that I'd like to mention that equation (3), which I got from the Disney paper [DS], also has to be multiplied with a "normalization" term which is shown at the top of page 25 (eq. 3, the left fraction on the right side). This wasn't made clear to me until it was mentioned in [PM].
This is my usual experience with reading papers of this kind. Often I need multiple sources in order to fill in the gaps of my understanding.

Testing in my Shadertoy demo, the specular highlight (D-term) now behaves more or less as I would expect. Still got aliasing at the penumbra which appears to be due to the G-term (which handles micro facet shadowing), so that's what I'll be working on next.

!til &learningjam2024 Linking to the paper I mentioned in the recap stream. The best resource on the subject I've found so far.
https://blog.selfshadow.com/publications/s2013-shading-course/hoffman/s2013_pbs_physics_math_notes.pdf

!til &learningjam2024 Got started on implementing a material demo in Shadertoy but had to realize that it's going to take its time, so a brief summary will have to suffice. I've put it up for download on my site.
https://unlitart.com/download/HMN_LearningJam2024_BRDF_Summary.pdf
Big thanks to the HMN team for arranging this event. To be honest the concept didn't excite me too much when it was announced but it turned out to be a great opportunity to check off something from the mental bucket list.

!til &learningjam2024 Currently reading through this paper.
https://media.disneyanimation.com/uploads/production/publication_asset/48/asset/s2012_pbs_disney_brdf_notes_v3.pdf
The scope has shifted from understanding BRDF's to learn about material models based on the micro facet model, which are nowadays commonly employed in both games and films, what is usualy referred to as "physically based".
As mentioned before, BRDF simply denotes a function that returns reflectance based on view, and light direction, so to learn anything of substance we need to look at the models themselves. The time has come where I finally study lighting. I'm thankful for this jam giving me the incentive.

!til &learningjam2024 The concept of BRDF's turned out simple enough. It's a function that returns the amount of light being reflected based on a given direction pointing towards the viewer and a direction pointing towards the light source. Whether they are vectors or angles based on surface normal seems to vary between sources.
A BRDF is meant to be a self contained thing in the rendering algorithm that can be swapped at will. Basically it's an abstraction.
In practice a BRDF implements some material model. Apparently it's common to combine one for diffuse and one for specular. Any old material model you might have heard of (Lambert, Phong etc) counts as a BRDF. Nowadays BRDF's are usually based on the micro facet model, both in games and film.
This is currently my primary source, which I'm still reading through.
https://boksajak.github.io/files/CrashCourseBRDF.pdf