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Spectral Ray Tracing

larswander.com

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Re: Spectral Ray Tracing

#11

Post by Klaster_1 »

zokier wrote: post #7

Spectral rendering imho is good example how ray tracing in itself is not the end-game for rendering, it's more just starting point. Occasionally I see sentiment that with real-time ray tracing rendering is a solved problem, but imho it's far from truth. Afaik most spectral rendering systems do not do (thin-film) interference or other wave-based effects, so that is another frontier. Reality has surprising amount of de…

The closer rendering comes closer to underlying physical principles, the more game engines will become world simulation engines. Various engine parts commonly seen today will converge towards a common point, where, for example, we'll observe less distinction between physics and rendering layers. I wonder if this trend can be traced to some degree even today. Several orders of compute growth later, we'll look upon current abstractions in the same manner as on the 30 years old state of the art, shaped by technical limitations of the yesteryear, obvious in hindsight. Love the perspective this puts the things into.

Re: Spectral Ray Tracing

#12

Post by dagmx »

Some examples of Spectral ray tracers

Mitsuba is an open source research renderer with lots of cool features like differentiable rendering. https://www.mitsuba-renderer.org/

Maxwell has two spectral modes of varying accuracy. The more complex method is often used for optics. https://maxwellrender.com/

Manuka by Wētā FX is spectral and has been used in several feature films https://dl.acm.org/doi/10.1145/3182161 and https://www.wetafx.co.nz/research-and-tech/technology/manuka

Re: Spectral Ray Tracing

#13

Post by dagmx »

raytopia wrote: post #6

Does anyone know if someone has attempted real time spectral rendering? I've tried finding information before but have never had any luck.

Real-time is unfortunately a sort of vague term.

If you mean raster rendering pipelines then I don’t believe it’s possible because the nature of the GPU pipelines precludes it. You’d likely need to make use of compute shaders to create it at which point you’ve just written a patthtracer anyway.

If you mean a pathtracer , then real-time becomes wholly dependent on what your parameters are. With a small enough resolution, Mitsuba with Dr.JIT could theoretically start rendering frames after the first one in a reasonable time to be considered realtime.

However the reality is just that even in film, with offline rendering, very few studios find the gains of spectral rendering to be worth the effort. Outside of Wētā with Manuka , nobody else really uses spectral rendering. Animal Logic did for LEGO movie but solely for lens flares.

The workflow change to make things work with a spectral renderer and the very subtle differences are just not worth the high increase in render time

Re: Spectral Ray Tracing

#14

Post by 6mian »

If you want to play with ray tracing implementation, it's surprisingly easy to write one by yourself. There's a great free book (https://raytracing.github.io/books/RayTracingInOneWeekend.ht...) or, if you know a bit of Unity a very nice GPU-based tutorial (https://medium.com/@jcowles/gpu-ray-tracing-in-one-weekend-3...). The Unity version is easier to tinker with, because you have scene preview and other GUI that makes moving camera around so much easier. There are many implementations based of these sources if you don't want to write one from scratch, although doing so is definitely worth it.

I spent some great time playing with the base implementation. Making the rays act as particles* that bend their path to/away from objects, making them "remember" the last angle of bounce and use it in the next material hit etc. Most of them looked bad, but I still got some intuition what I was looking at. Moving the camera by a notch was also very helpful.

A lot of fun, great for a small recreational programming project.

* Unless there's an intersection with an object, then set the maximum length of the ray to some small amount, then shoot many rays from that point around and for each hit apply something similar to the gravity equation. Of course this is slow and just an approximation, but it's easy and you can implement a "black hole" type of object that will bend light in the scene.

Re: Spectral Ray Tracing

#16

Post by magicalhippo »

zokier wrote: post #7

Spectral rendering imho is good example how ray tracing in itself is not the end-game for rendering, it's more just starting point. Occasionally I see sentiment that with real-time ray tracing rendering is a solved problem, but imho it's far from truth. Afaik most spectral rendering systems do not do (thin-film) interference or other wave-based effects, so that is another frontier. Reality has surprising amount of de…

> Reality has surprising amount of detail.

Another one that few implement, and which can have a quite noticeable effect in certain scenes, is polarization of light[1].

[1]: https://www.giangrandi.ch/optics/polarizer/polarizer.shtml

Re: Spectral Ray Tracing

#17

Post by magicalhippo »

uoaei wrote: post #9

Are there any good resources for spectral ray tracing for other frequencies of light, e.g. radio frequencies?

What are the applications you have in mind?

I'm no RF guy, but I imagine you quickly will have to care about areas where the wavelike properties of EM radiation dominates, in which case ray tracing is not the right tool for the job.

Re: Spectral Ray Tracing

#18

Post by alkonaut »

dagmx wrote: post #12

Some examples of Spectral ray tracers Mitsuba is an open source research renderer with lots of cool features like differentiable rendering. https://www.mitsuba-renderer.org/ Maxwell has two spectral modes of varying accuracy. The more complex method is often used for optics. https://maxwellrender.com/ Manuka by Wētā FX is spectral and has been used in several feature films https://dl.acm.org/doi/10.1145/3182161 and h…

If you want to look under the hood and find the big production ones like too complex, I can recommend peeking at this one. It's a great example example of just the minimum of a spectral path tracer https://github.com/TomCrypto/Lambda

Re: Spectral Ray Tracing

#20

Post by pixelpoet »

dagmx wrote: post #12

Some examples of Spectral ray tracers Mitsuba is an open source research renderer with lots of cool features like differentiable rendering. https://www.mitsuba-renderer.org/ Maxwell has two spectral modes of varying accuracy. The more complex method is often used for optics. https://maxwellrender.com/ Manuka by Wētā FX is spectral and has been used in several feature films https://dl.acm.org/doi/10.1145/3182161 and h…

There's also Indigo Renderer and the open source LuxRender:

https://indigorenderer.com

https://luxcorerender.org

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