I went through several of your OpenGL videos last night. I have to say you present some of the most clear and correct content on the topic I have ever come across. No waffling, straight to the point and easy to understand. Thank you
Brian, I greatly appreciate the work you put into this subject and the accompanying book. It is concise, explained well and most of all touches on topics without over complicating them. Kudos to you!
5:50 k is a function of alpha, (alpha+1)^2/8 for a direct light source and alpha^2/2 for image-based lighting Regarding the term GGX, this is so funny, it cracks me up every time I see it. Nobody knows what it means. As in not a single person on earth. My theory: the guy who invented it was drunk and wrote it down. The next morning, he couldn't remember anything but still sent the paper to Disney. That's what happened.
If i'm not mistaken, the division by PI in the diffuse component and division by 4 * NdotL * NdotV is the normalization factor for keeping our NDF normalized (equal to 1)
Depending on the source, some use Pi, other use 4... I didn't find an explanation on why each value, but they're used. I think Disney and UE4 used 4, until Epic went to Pi in UE5
The line kD = 1.0 - metallic threw me off at first, but maybe now I understand. So kD+kS=1 is for dielectrics, however, conductors have also some kind of a grounding term (e.g. kD+kS+kConductiveGrounding=1)?
What boggles my mind: is not a N dot V always negative ? Since N points outwards of object and V inwards, so the angle is always greater than 90° isn't it ?
Not if those textures are already in the sRGB color space. GL can omit that transform of you have already the texture expressed in sRGB. But that isn't said
4:18 how can the sphere reflect light from a point of its surface that is not even exposed to light? images for α 0.1, 0.3 and 0.5 i can accept, but 0.8 and 1.0 must be incorrect?
In my opinion its right. he talking about roughness on the left its almost clear surface "mirror" this is how light should looks like in mirror and with higher roughness its starts spreading and bouncing into random direction instead of directly to "camera"
