I found this application of refraction particularly intriguing. With a higher refractive index in the water than in the air, the light would travel towards a smaller angle the light ray formed with the normal vector, regardless what angle the light 'enters' water from the air. Here are some interesting examples I found with the air-water refractive rate and snell's window: http://www.divephotoguide.com/underwater-photography-techniques/article/underwater-photographer-s-guide-snell-s-window/.
Adding to that, this gets me to think about how to render a scene underwater. Because underwater there is always turbulence, lights do not travel in a straight path. This is why underwater images can sometimes appear to be distorted. For example, http://area.areaware.com/liquid-body/. I wonder how should we render this distortion?
I'm kind of confused about what total internal reflection is. In project 3-2 part 1, we just reflected if we got total internal reflection, but I don't think I really understand what it is. Also, since the light is coming from every direction, this is environment light right?
@jchen12197 Total internal reflection is when a ray of light cast from within a medium doesn't actually exit the medium; rather, it bounces back into the medium because the angle of incidence is > than the critical angle. The critical angle for water is ~48.6 degrees. So when looking up from underwater, your field of vision is restricted -- you don't have a full 180 degree view; instead you see a circle formed by a cone of 48.6*2 = 97.2 degrees because at angles beyond this, total internal reflection occurs and you just see light reflected from elsewhere underwater.
This excerpt helped clarify this slide for me: https://books.google.com/books?id=B8S3DAAAQBAJ&pg=PT171&lpg=PT171&dq=critical+angle+97.2&source=bl&ots=Q_M1yMivFf&sig=ACfU3U2qCHqcPgp9rVUCyCuE-pnrvj5-9A&hl=en&sa=X&ved=2ahUKEwiWwvz08b_hAhVhFTQIHV92Be8Q6AEwD3oECAcQAQ#v=onepage&q=critical%20angle%2097.2&f=false