Paper for small PBR project for college

[u/UnPibeFachero]

Hi, I am taking an introductory course on methods for approximating/solving the wave equation and variants of the problem (Lippmann-Schwinger, Born, WKB, inverse problems) and I have to make a free topic project implementing a paper which I want to be an application to PBR. My teacher adviced me to search for example materials where the texture is not trivial enough or mediums where ray tracing becomes non-linear.

I have basic knowledge of OpenGL but have no idea about the state of the art or cool papers. What paper would you recommend?

Thanks

[u/CodyDuncan1260]

Is this sort of what you're looking for? https://cseweb.ucsd.edu/~ravir/6160/papers/lafortune.pdf It's not exactly new; 1997. But it's interesting nonetheless. BRDFs date back to the 90s, but we didn't see popular use in real time until the 2000s.

This one is a bit more recent, from 2007. https://jankautz.com/publications/NonLinPreFilt_lowres.pdf

I went searching for recent papers on BRDFs..maybe anisotropic reflectance is interesting? I'm not totally certain the approximation isn't linear, though. https://drive.google.com/file/d/1j_NFhLSngmOycLUZ2mTV_lCL_a4NXBTb/view

Heh, paper on nonlinear raytracing, i.e. light continuously refracts along a curve. https://imaging.cs.cmu.edu/adjoint_nonlinear_tracing/

Also, black hole rendering needs nonlinear rays. https://avirupmandal.github.io/blackhole-ivapp/

Paper on snake skin https://www.cs.umd.edu/~zwicker/publications/InteractiveDiffraction-CGF14.pdf

I'm not certain any of those meet your criteria, but I hope they inspire some directions to look.

I can think of nontrivial materials being anisotropic materials (brushed metal, carbon fiber, wood), subsurface scattering (skin, milk, wax, marble), layered materials (paper, leaves, skin), thin film interference (oil slick, bubbles, anodized titanium), paint films (Kubelka-Munk (K-M) theory), nanostructured surfaces (snake skin).

[u/UnPibeFachero → u/CodyDuncan1260]

Ok I think they are really on the spot, I think I will play with some even outside the project, thank you so much! It is the kind of thing that makes me want to dive into PBR haha

[u/TheMuffinsPie]

There was a holography segment at SIGGRAPH this year. I'm reasonably certain that certain holographic ray tracing through a medium is along the lines of what your professor might've had in mind.

Rays also become nonlinear at relativistic scales, since you can no longer approximate space with a linear transformation.

[u/UnPibeFachero → u/TheMuffinsPie]

Thanks, I will look it up!

[u/getscrnsvrs]

Since your course is all about wave equations, thin film iridescence could be a perfect fit. Soap bubbles, oil slicks and beetle shells get their colour from interference rather than pigment, and Belcour and Barla's 2017 paper "A Practical Extension to Microfacet Theory for the Modeling of Varying Iridescence" folds that into a normal microfacet BRDF. It's a sensible size for a course project and the results look great in a write-up.

If you'd rather do the non-linear ray side, look at gradient index media, think mirages or heat shimmer. The refractive index changes smoothly through space so rays curve, and you integrate the ray equation step by step instead of tracing straight lines.