4th edition of Physically Based Rendering is now freely available online

Pretty sure the 3rd edition already contained that, no? At that time (not sure if that's still the case now) the choice was a compile time option, iirc.

How do you deal with materials in a spectral renderer? Use something like a gaussian for each rgb component?

Firstly, "physically based rendering" has become a term of the art. This means that today, it's correct to use it to mean this specific thing no matter what the grammar rules say about the phrase. Furthermore, another phrase that would mean the same thing and is grammatically correct (like "physics based rendering"), is less correct in this context because it loses the specific meaning attached to the term of the art.

Secondly, "physically" is an adverb. This means it is grammatically correct for it to preceed "based" if used as a verb. If "based" could only be used as an adjective, then you're right, "physics based rendering" would be more correct.

Anybody more knowledgeable feel free to correct me!

The ship has sailed on this term of art, but as a native English speaker, I agree with you that it's ungrammatical. I would use a hyphen, though: "physics-based." This answer agrees with you (and me): https://english.stackexchange.com/a/428679.

Here's one way to think about _why_ it sounds wrong. "Physically based" would mean that "physically" is the answer to the question "How is it based?" To a native English speaker, that question sounds odd. A more natural question is "What is it based on?" To answer that question, you need a noun: "It's based on physics." Hence the construct "physics-based," like "evidence-based medicine" or "merit-based scholarships."

English is my native tongue, but it doesn’t really help analyze this type of thing. Titles often use terms-of-art and shortened phrases.

But, fwiw, to my eyeballs “Physics based rendering techniques,” because it uses the word Physics, as in the whole big field of study, looks like it is a Physics text that happens to include a bit of rendering.

“Physically based rendering techniques” seems like it is a work about rendering techniques, which will draw a lot from physics.

It should be "physically based" since it's about rendering based on how light works physically, in the real world. See https://en.wikipedia.org/wiki/Physically_based_rendering

Now with SYCL and CUDA supporting most C++ proper, using it instead of shading languages is starting to be a thing.

Although I do think shading languages are still more appropriate, or other kind of more high level modelling.

In any case as long there is a toolchain to generate SPIR-V or PTX, there is a way for the favorite language into the GPU.

PBR is not really a new rendering stack or a new framework, but a way of thinking about the asset creation process and shader development that allows for more of a separation between material models and lighting. There were a few things associated with the PBR trend that do not have anything, strictly, to do with PBR, but came along for the ride and helped things:

* The recognized importance of specularity in materials, outside of the ones that are obviously shiny. Something something, everything has fresnel. Look at your wood desk, or your matte walls, and you'll notice you'll see some glossy reflections on them.

* We switched away from art workflows that generated normal maps out of Photoshop filters, and towards programs and workflows that kept a much better idea of 3D-ness throughout the stack. Substance Painter, Substance Designer, and baking normal maps from ZBrush are a huge and understated part of the PBR transformation.

* We changed around our terminology, and put more floorboards underneath the rugs. e.g. in the before times, if you had a material that was "unlit", it probably just displayed as the diffuse color texture, and nothing else. That doesn't make sense, that's the reflectance properties of the material. So we changed things around to be lights-first, and a lot of things fell into place from that. Together with that, basic kinds of global illumination started becoming more and more mainstream through probes.

* We redesigned lighting and shading models to use more physics in them. Out went the observational Phong and Blinn-Phong, and in came the more empirical Trowbridge-Reitz and GGX. We fixed lights to have accurate inverse-square-law falloffs. We replaced (or are in the process of replacing) point lights and spotlights with area lights. And GI became a reliable tool.

Before the PBR revolution, things were far more scattershot, though there were definitely attempts at trying to integrate physics. Half-Life 2, Unreal 3, and Halo Reach might not have strictly been "PBR" by modern standards, but definitely had a lot of good ideas floating around it with regards to lighting.

So PBR has become the default in the industry since starting around 2009 but really took off around 2013 - 2014. It was adopted because it could represent a larger range of physical surfaces then previous models while looking more consistent and being easier to understand [0]. Before then most 3d games either used Phong or Blinn-Phong [1] but they were hard to control for artists and they didn't really represent many materials very well.

[0] https://marmoset.co/posts/physically-based-rendering-and-you...

[1] https://en.wikipedia.org/wiki/Blinn%E2%80%93Phong_reflection...

My understanding is that in the past you could try to make some random shader and tune it to make it look good/real in some condition, but then it will not look good in other conditions. With PBR you take more complex shaders, but they are based on real physics, and they will look good in almost all conditions.

Veach thesis was truly years ahead.

veach thesis gives me "damn I wish I could read" moments

I love the Watt and Watt "Advanced Animation and Rendering Techniques" book as well; it was IMHO the best book on those topics in its time.

Do you mean "Literate" programming style?

http://literateprogramming.com/

That didn't get any attention, otherwise the dupe detector would've come into play.

In the book it explains that it is a homegrown tool. It’s likely secret sauce they do not release publicly.