Physically based rendering from first principles • Hacker News Board

Re: Physically based rendering from first principles

#41

Post by tzumaoli » Wed, Sep 03, 2025, 12:39 AM UTC

kelseyfrog wrote: post #39

imadr wrote: post #38

Earlier quoted context omitted.

If i’m not mistaken that’s in part how they came up with micro facet models, or at least to verify their accuracy. Take this paper for example https://www.cs.cornell.edu/~srm/publications/EGSR07-btdf.pdf Real life measures are also useful for inverse rendering.

Interesting link, thank you! It looks like a good model for lower incident angles but begins to diverse at higher angles. There's also one huge caveat - it relates the GGX model to real world ground glass. Obviously it's important to compare like to like. However, very few materials in the real world are ground glass. Looking around my surroundings, I see painted drywall, wood, paper, plastics, and textiles. It would…

The same Cornell group has done more research in this area. Here is one for capturing the microgeometry of metals https://www.cs.cornell.edu/Projects/metalappearance/ Here's another paper from a different group on capturing the microgeometry using a lot of LED lights https://svbrdf.github.io/publications/MicroLightStage/Micros...

But I agree there should be a lot more work in this area!!

Re: Physically based rendering from first principles

#42

Post by asdaqopqkq » Wed, Sep 03, 2025, 12:49 AM UTC

godelski wrote: post #9

I'm not a fan of how people talk about "first principles" as I think it just leads to lots of confusion. It's a phrase common in computer science that makes many other scientific communities cringe. First principles are things that cannot be reduced and you have to have very good justifications for these axioms. The reason the other scientific communities cringe is because either (most likely case) it's being used im…

[flagged]

Re: Physically based rendering from first principles

#43

Post by grg0 » Wed, Sep 03, 2025, 1:55 AM UTC

magicalhippo wrote: post #23

imadr wrote: post #12

Earlier quoted context omitted.

Thanks for the constructive criticism! A few points I'd like to discuss: Let's suppose the aim of the article was indeed to learn PBR from first principles, what would it look like? Quantum electrodynamics? I think there is merit in exploring different physical models for fun and scientific curiosity (like I mentioned in the first chapter). I (personally) feel that it's boring to just dump equations like Snell's law…

> I dislike "Physically Based Rendering: From Theory To Implementation", I personally think that the literate programming approach of the book is way too confusing and disorganized. Interesting. Personally it's by far the best programming related book I've read. I didn't mind the literal programming, and I loved how it dove fairly deep into the math and physics but also into the details of implementing the math. The…

I agree with OP and find the literal programming in that book incredibly distracting and annoying. I prefer the theory up front and the code later. "Ray Tracing From the Ground Up" does a much better job in my opinion (although it also only covers a fraction of the topics in the PBR book.)

Re: Physically based rendering from first principles

#44

Post by chermi » Wed, Sep 03, 2025, 2:47 AM UTC

imadr wrote: post #21

delta_p_delta_x wrote: post #19

Earlier quoted context omitted.

> Let's suppose the aim of the article was indeed to learn PBR from first principles, what would it look like? Quantum electrodynamics? Something like that, yes. A truly from-first-principles treatment of photon-surface interactions would involve an extremely deep dive into quantum numbers, molecular orbitals, solid state physics and crystal lattices (which are metals), including a discussion about how electron waves…

I might be a stupid question but how hard would that be to explain, and to understand? If you had to teach an alien from another universe physically based rendering: - In an exhaustive manner and, - You're only allowed to explain something if it derives from something more "fundamental" until we reach the most comprehensive physical models we have How hard would be the math behind it for example? Because realisticall…

No, Feynman lectures won't get you there.

Re: Physically based rendering from first principles

#45

Post by chermi » Wed, Sep 03, 2025, 2:50 AM UTC

MangoToupe wrote: post #16

godelski wrote: post #9

I'm not a fan of how people talk about "first principles" as I think it just leads to lots of confusion. It's a phrase common in computer science that makes many other scientific communities cringe. First principles are things that cannot be reduced and you have to have very good justifications for these axioms. The reason the other scientific communities cringe is because either (most likely case) it's being used im…

I think Musk was the first person I noticed to really abuse this phrase. Not that it's not a useful phrase—of course it is. But it seems like it's an abuse of what should be called "core agreed assumptions" or something.

Lol apparently reasoning by analogy is first principles to him -- see human drivers using only vision therefore no lidar somehow being "first principles".

Re: Physically based rendering from first principles

#46

Post by Krei-se » Wed, Sep 03, 2025, 5:49 AM UTC

godelski wrote: post #13

jiggawatts wrote: post #10

Earlier quoted context omitted.

The author went down to the electromagnetic wave theory of light. How much more “first principles” could this article be!?

> How much more “first principles” could this article be!? I think you've answered your own question and demonstrated my point. See my third sentence. The notion of " more 'first principles'" is like asking who's before the first person in line. If there's more people in front, then they aren't the first person in line and if there aren't, well you're right, how can you be more first? But I think we both know this is…

i have a similar background to OP and went into physics mostly by accident learning geometric algebra, so i wonder why it's shunned skipping the deductive concepts you have to forget/correct later anyways - for me it makes a lot more sense building from the most abstract ground i can barely stand on.

Re: Physically based rendering from first principles

#47

Post by deadbabe » Wed, Sep 03, 2025, 6:47 AM UTC

godelski wrote: post #9

I'm not a fan of how people talk about "first principles" as I think it just leads to lots of confusion. It's a phrase common in computer science that makes many other scientific communities cringe. First principles are things that cannot be reduced and you have to have very good justifications for these axioms. The reason the other scientific communities cringe is because either (most likely case) it's being used im…

This comment eliminated any motivation I had to read the original article.

Re: Physically based rendering from first principles

#48

Post by godelski » Wed, Sep 03, 2025, 6:51 AM UTC

asdaqopqkq wrote: post #42

godelski wrote: post #9

I'm not a fan of how people talk about "first principles" as I think it just leads to lots of confusion. It's a phrase common in computer science that makes many other scientific communities cringe. First principles are things that cannot be reduced and you have to have very good justifications for these axioms. The reason the other scientific communities cringe is because either (most likely case) it's being used im…

[flagged]

Published a bunch of papers, created state of the art machine learning models you might have used, wrote blog posts there's a good chance you've read, publishing open sourced software, made companies millions of dollars while not getting a dime and having random internet users fail to see the irony of telling us we're useless by using a computer. How do you think we got here?

Re: Physically based rendering from first principles

#49

Post by godelski » Wed, Sep 03, 2025, 6:52 AM UTC

Krei-se wrote: post #46

godelski wrote: post #13

Earlier quoted context omitted.

> How much more “first principles” could this article be!? I think you've answered your own question and demonstrated my point. See my third sentence. The notion of " more 'first principles'" is like asking who's before the first person in line. If there's more people in front, then they aren't the first person in line and if there aren't, well you're right, how can you be more first? But I think we both know this is…

i have a similar background to OP and went into physics mostly by accident learning geometric algebra, so i wonder why it's shunned skipping the deductive concepts you have to forget/correct later anyways - for me it makes a lot more sense building from the most abstract ground i can barely stand on.

Mostly because it is like trying to teach people how to swim in the deep end. It's definitely possible but not a great idea for the majority of people.

Do you really want to start learning physics from String Theory? You could, but it isn't a great idea. Even if you replace ST with an alternative proposed ToE.

Re: Physically based rendering from first principles

#50

Post by godelski » Wed, Sep 03, 2025, 6:54 AM UTC

chermi wrote: post #45

MangoToupe wrote: post #16

Earlier quoted context omitted.

I think Musk was the first person I noticed to really abuse this phrase. Not that it's not a useful phrase—of course it is. But it seems like it's an abuse of what should be called "core agreed assumptions" or something.

Lol apparently reasoning by analogy is first principles to him -- see human drivers using only vision therefore no lidar somehow being "first principles".

  > see human drivers using only vision

Which is such a naive assumption too! Do you not feel the road? Listen to the road? I mean you might not think you do the latter but I bet if you closed your eyes you could get a decent estimate of how fast you are going.