Thread by @rothgar, After watching Pixar's Cars for the 1000th time I'm still not sick [...]

After watching Pixar's Cars for the 1000th time I'm still not sick of it. It's one of my favorite animated films full of easter eggs and unique story telling and technical challenges.

It also shares a mathematical method used with the atomic bomb!

Let's go for a ride

First of all, how would you tell a story where every character was just a head? No arms, legs, bodies. Just eyes and a mouth.

Because that's pretty much what Cars is. It's a master class in facial expression and voice acting.

Remember, that other animated cars typically used headlights for eyes and wipers for eyebrows. Cars just made up their own "eyebrows" but it totally works.

You should also read about the Chevron cars because they're really cool too https://www.chevronwithtechron.com/cars

Of course the 1952 short Susie the Little Blue Coupe helped inspire the character design.

So back to Cars, I don't watch nascar but I've seen enough clips and been around people who do to know Pixar really did their homework to make this look real.
I swear I've seen this in a race before

Maybe not that, but watch this

75,000 cars!

I counted them

This is my favorite shot in the entire movie

It's just so perfect!

Intentional imperfection makes the world so much more believable.

These are talking cars. No humans. No animals (carminals?).

And by taking an imperfection from our real world you believe this world can exist.

ICYMI https://twitter.com/rothgar/status/1271953761167015938?s=20

https://twitter.com/rothgar/status/1271953761167015938?s=20

I have to move ahead or this thread will be too long.

You see how they use color (or lack thereof) here. Compared to the vibrant colors of the race this world is dead. It has no beauty.

At least not in Lightning's eyes

But look at the colors later when Lightning falls in love with Radiator Springs

There are so many cool easter eggs in this whole part of the movie.

Like the tire treads in the sky
The car shaped clouds
Toy story clouds (they're all over)

This is my 2nd favorite scene. The lighting and reflections in this are amazing!
Remember this came out in 2006.

In 2006 you may have had one of these. The PowerMac G5 came out in 2006 which means Pixar was probably using G4s for Cars

The cruise is so great because it shows off the realistic light rendering are using ray tracing instead of traditional scanline rendering.
Seriously, it's super cool! You should go read the paper (PDF) https://graphics.pixar.com/library/RayTracingCars/paper.pdf

Pixar adapted RenderMan to use both scanline rendering AND ray tracing because computers couldn't ray trace full frames with available memory at the time

Scanline rendering relied on lighting and shadow maps which had to be created by artists. It was not easy with complex scenes

Ray tracing gives you
- realistic lighting from lots of sources. Some Cars scenes had thousands.
- Dynamic shadows (approximation with global illumination)
- reflections (especially close proximity self reflections)

Basically ray tracing makes light (and shadows) look more real

Cars needed it for large scenes, scenes with lots of light sources, and scenes with lots of reflections.

RenderMan used a hybrid rendering which basically did scanline rendering to determine how much detail they needed and ray tracing when they could afford to

The history of ray tracing in movies is in this paper (another PDF) https://graphics.pixar.com/library/PathTracedMovies/paper.pdf It goes into a lot of the details about how ray tracing works but also some of the challenges.

Like how do you render hair/fur with complex geometry with lights bouncing all over. How do you do fast/rough renders but also high quality finished renders when you have to bounce light from your eyes, through a window (camera), off objects, and back to a light source?

Rey tracing without enough light rays is really really noisy. How do you eliminate the noise? How do you add motion blur one picture at a time? How do you render clouds?

If you're really interested in ray tracing check out this video how the Hyperion renderer does it. (It's different than Renderman because a lot changed in ~10 years)

So, Cars. What did it have to do with the atomic bomb?

When they were making the bomb they wanted to make sure they wouldn't start a chain reaction but the math had way too many variables for the compute resources at the time.

They used the Monte Carlo method to take random samples of their variables and compute those to solve a deterministic problem. https://en.wikipedia.org/wiki/Monte_Carlo_method

Here's Monte Carlo method applied to solving pi

40+ years later Pixar used Monte Carlo method to determine which pixels they needed to shoot light beams through to reduce noise and get a realistic spread of light on their shots.