Are there any materials or objects that are canonically known as extremely difficult to trace light for? In lecture sushi is mentioned as harder because it internally reflects, is there anything worse?
Another example of difficult materials to trace could be a multi-layered material that reflects, refracts, and absorbs light at every level.
was trying to search for materials that are difficult to render and found this quote (That I found amusing):
In response to a question concerning what was the single hardest shot in “Shrek”, DreamWorks SKG principal and producer of “Shrek”, Jeffrey Katzenberg, stated, It’s the pouring of milk into
a glass. [Hiltzik and Pham 2001]."
As a person who makes 3D animation for fun, I think the property of the material definitely makes rendering challenging. Sometimes, though, it could also be about how they are grouped or shown in scenes. For example, if we render one strand of hair, that wouldn't be too difficult. But it becomes very complicated when you need to render the entire head because light bounces off in between each and every hair, making each strand absorb different amount of light.
It's so cool how much of a role light plays in materials. I find hair particularly interesting and I'm curious as to how it translates once you start to animate it.
Great discussions here!
Subsurface scattering is quite costly but there are some estimators (some better than others) for evaluating the light in these cases. And the milk pouring shot in Shrek is a great example of subsurface scattering.
Another material I could think of right off the top of my head is glitter. Linqi Yan was an 184 TA and he researched about them: https://sites.cs.ucsb.edu/~lingqi/ You can also find some of his work on hair rendering!
I heard skin is also expensive to render. Light penetrates skin in a weird way so that it glows red at certain angles and you have to account for the tiny pores on skin too.