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At some point every render-engine builder goes through the exercise of imagining purely physically-modeled photonic simulation. How soon one gives up on this c

At some point every render-engine builder goes through the exercise of imagining purely physically-modeled photonic simulation. How soon one gives up on this computationally intractable task with limited marginal return on investment is a signifier of wisdom/exhaustion. And, yes, I've gone way too far down this road in the past.

solardev 3y ago
Not being a graphics person, is this what hardware ray tracing is, or is that something different?
- ReactiveJelly 3y ago
  Even the ray tracing / path tracing is half-fake these days cause it's faster to upscale and interpolate frames with neural nets. But yeah in theory you can simulate light realistically
  - dexwiz 3y ago
    It’s still a model at the end of the day. Material properties like roughness are approximated with numerical values instead of being physical features. Also light is REALLY complicated when you get close to a surface. A light simulation that properly handles refraction, diffraction, elastic and inelastic scattering, and anisotropic material properties would be very difficult to build and run. It’s much easier to use material values found from experimental results.
    - dahart 3y ago
      If I understood Feynman’s QED at all, light gets quite simple once you get close enough to the surface. ;) Isn’t the idea was that everything’s a mirror? It sounds like all the complexity comes entirely from all the surface variation - a cracked or ground up mirror is still a mirror at a smaller scale but has a complex aggregate behavior at a larger scale. Brian Green’s string theory talks also send the same message, more or less.
      - Sharlin 3y ago
        Sure, light gets quite simple as long as you can evaluate path integrals that integrate over the literally infinite possible paths that each contributing photon could possibly take! Also, light may be simple but light interaction with electrons (ie. matter) is a very different story!
        arbitrandomuser 3y ago
        Don't the different phases from all the random path more or less cancel out , and significant additions of phases only come from paths near the "classical" path? I wonder if this reduction would still be tractable on gpus to simulate diffraction
        dahart 3y ago
        That’s what I remember from QED, the integrals all collapse to something that looks like a small finite-width Dirac impulse around the mirror direction. So the derivation is interesting and would be hard to simulate, but we can approximate the outcome computationally with extremely simple shortcuts. (Of course, with a long list of simplifying assumptions… some materials, some of the known effects, visible light, reasonable image resolutions, usually 3-channel colors, etc. etc.) I just googled and there’s a ton of different papers on doing diffraction in the last 20 years, more that I expected. I watched a talk on this particular one last year: https://ssteinberg.xyz/2023/03/27/rtplt/ https://ssteinberg.xyz/2023/03/27/rtplt/
      - dexwiz 3y ago
        Orbital shapes and energies influence how light interacts with a material. Yes, once you get to QED, it’s simple. Before that is a whole bunch of layers of QFT to determine where the electrons are, and their energy. From that, there are many emergent behaviors. Also QED is still a model. If you want to simulate every photon action, might as well build a universe.
- bufferoverflow 3y ago
  Rayteacing doesn't simulate light, it simulates a very primitive idea of light. There's no diffraction, no interference patterns. You can't simulate the double-slit experiment in a game engine, unless you explicitly program it. Our universe has a surprising amount of detail. We can't even simulate the simplest molecular interactions fully. Even a collision of two hydrogen atoms is too hard - time resolution and space resolution is insanely high, if not infinite.
  - zokier 3y ago
    > You can't simulate the double-slit experiment in a game engine, unless you explicitly program it. Afaik you can't even simulate double-slit in high-end offline VFX renderers without custom programming
  - Sharlin 3y ago
    And what’s more, it simulates a very primitive idea of matter! All geometry is mathematically precise, still made of flat triangles that only approximate curved surfaces, every edge and corner is infinitely sharp, and everything related to materials and interaction with light (diffuse shading, specular highlights, surface roughness, bumpiness, transparency/translucency, snd so on) are still the simplest possible models that five a somewhat plausible look, raytraced or not.
  - smolder 3y ago
    I wanted to make a dry joke about renderers supporting the double slit experiment, but in a sense you beat me to it.
    - hoseja 3y ago
      There sure has been a lot of slits simulated in Blender.
  - zokier 3y ago
    Btw there is some movement towards including wave-optics into graphics instead of traditional ray-optics: https://ssteinberg.xyz/2023/03/27/rtplt/ https://ssteinberg.xyz/2023/03/27/rtplt/
hutzlibu 3y ago
I have heard the hope expressed, that quantum computers might solve that one day, but I believe it, once I see it. Till then, I have some hope, that native support for raytracing on the GPU will allow for more possibilities ..
deleted 3y ago
[deleted]

solardev 3y ago

Not being a graphics person, is this what hardware ray tracing is, or is that something different?

ReactiveJelly 3y ago
Even the ray tracing / path tracing is half-fake these days cause it's faster to upscale and interpolate frames with neural nets. But yeah in theory you can simulate light realistically
- dexwiz 3y ago
  It’s still a model at the end of the day. Material properties like roughness are approximated with numerical values instead of being physical features. Also light is REALLY complicated when you get close to a surface. A light simulation that properly handles refraction, diffraction, elastic and inelastic scattering, and anisotropic material properties would be very difficult to build and run. It’s much easier to use material values found from experimental results.
  - dahart 3y ago
    If I understood Feynman’s QED at all, light gets quite simple once you get close enough to the surface. ;) Isn’t the idea was that everything’s a mirror? It sounds like all the complexity comes entirely from all the surface variation - a cracked or ground up mirror is still a mirror at a smaller scale but has a complex aggregate behavior at a larger scale. Brian Green’s string theory talks also send the same message, more or less.
    - Sharlin 3y ago
      Sure, light gets quite simple as long as you can evaluate path integrals that integrate over the literally infinite possible paths that each contributing photon could possibly take! Also, light may be simple but light interaction with electrons (ie. matter) is a very different story!
      - arbitrandomuser 3y ago
        Don't the different phases from all the random path more or less cancel out , and significant additions of phases only come from paths near the "classical" path? I wonder if this reduction would still be tractable on gpus to simulate diffraction
        dahart 3y ago
        That’s what I remember from QED, the integrals all collapse to something that looks like a small finite-width Dirac impulse around the mirror direction. So the derivation is interesting and would be hard to simulate, but we can approximate the outcome computationally with extremely simple shortcuts. (Of course, with a long list of simplifying assumptions… some materials, some of the known effects, visible light, reasonable image resolutions, usually 3-channel colors, etc. etc.) I just googled and there’s a ton of different papers on doing diffraction in the last 20 years, more that I expected. I watched a talk on this particular one last year: https://ssteinberg.xyz/2023/03/27/rtplt/ https://ssteinberg.xyz/2023/03/27/rtplt/
    - dexwiz 3y ago
      Orbital shapes and energies influence how light interacts with a material. Yes, once you get to QED, it’s simple. Before that is a whole bunch of layers of QFT to determine where the electrons are, and their energy. From that, there are many emergent behaviors. Also QED is still a model. If you want to simulate every photon action, might as well build a universe.
bufferoverflow 3y ago
Rayteacing doesn't simulate light, it simulates a very primitive idea of light. There's no diffraction, no interference patterns. You can't simulate the double-slit experiment in a game engine, unless you explicitly program it. Our universe has a surprising amount of detail. We can't even simulate the simplest molecular interactions fully. Even a collision of two hydrogen atoms is too hard - time resolution and space resolution is insanely high, if not infinite.
- zokier 3y ago
  > You can't simulate the double-slit experiment in a game engine, unless you explicitly program it. Afaik you can't even simulate double-slit in high-end offline VFX renderers without custom programming
- Sharlin 3y ago
  And what’s more, it simulates a very primitive idea of matter! All geometry is mathematically precise, still made of flat triangles that only approximate curved surfaces, every edge and corner is infinitely sharp, and everything related to materials and interaction with light (diffuse shading, specular highlights, surface roughness, bumpiness, transparency/translucency, snd so on) are still the simplest possible models that five a somewhat plausible look, raytraced or not.
- smolder 3y ago
  I wanted to make a dry joke about renderers supporting the double slit experiment, but in a sense you beat me to it.
  - hoseja 3y ago
    There sure has been a lot of slits simulated in Blender.
- zokier 3y ago
  Btw there is some movement towards including wave-optics into graphics instead of traditional ray-optics: https://ssteinberg.xyz/2023/03/27/rtplt/ https://ssteinberg.xyz/2023/03/27/rtplt/

hutzlibu 3y ago

I have heard the hope expressed, that quantum computers might solve that one day, but I believe it, once I see it. Till then, I have some hope, that native support for raytracing on the GPU will allow for more possibilities ..

deleted 3y ago

[deleted]