Main content

## Pixar in a Box

### Course: Pixar in a Box > Unit 8

Lesson 1: Geometry of dinosaur skin- Start here!
- Introduction to Patterns
- What are shading packets?
- Shading Packets
- Voronoi Partition
- Constructing a Voronoi partition
- Distributing sites randomly
- Poisson disc process
- Modeling dino skin
- Make your own dino skin 1
- Getting to know Ana
- Getting to know Beth

© 2023 Khan AcademyTerms of usePrivacy PolicyCookie Notice

# Distributing sites randomly

What is the best way to distribute points in a Voronoi pattern? With the Poisson disk process, we balance randomness and structure by introducing a minimum site distance parameter that ensures points are not too close together. This gives us a smoother distribution and a more natural-looking pattern! You can explore the interactive program used in this video here and here.

## Want to join the conversation?

**Interactive programs used in the video**:

Voronoi partition with different distributions: https://www.khanacademy.org/pixar/voronoi-with-different-distributions/5994481558355968

Poisson disc sampling: https://www.khanacademy.org/computer-programming/poisson-disc-sampling-animation/5205033722707968(25 votes)- What is the dino film that is shown all the time called :D ?(9 votes)
- It's "The Good Dinosaur", one of Pixar's most recent movies.(11 votes)

- 0:46: Arlo is a she? I think there's a mistake(7 votes)
- In the transcript it says, "0:43- [Woman 2] Well, let's check the shading packet.0:46- [Woman 1] Our Dino's quite young, so she has relatively few scales on her legs." They are talking about the dino's leg that was on the screen at the time, not Arlo in the movie.(5 votes)

- what is the no drop zone?(5 votes)
- It is what they were calling the area around the site where no points could be added randomly, to help prevent clumping.(4 votes)

- my real question is how do u determine if the shapes are not the same?(4 votes)
- That is so cool that everything has randomness!(2 votes)
- Does the technique "poisson" at1:28have anything to do with the fact that poisson is the French word for fish, or did it just so happen to be the name of the person who invented it, or something else entirely?(2 votes)
- The "Poisson distribution" is named after the French mathematician Siméon Denis Poisson who came up with it. His surname indeed comes from the word for "fish".(1 vote)

- and this has what to do with poisson distribution is alevel mathematics?(1 vote)
- h! this was typed at3:45.(1 vote)
- Hello thats cool(1 vote)

- Can't they use examples from nature? This way they can get pretty accurate templates, good colour patterns and controlled randomness, right? And you have an example for almost everything in nature. Why go through all this? (even though it's very informative). Plus wouldn't shading packets be hard to

make?(1 vote)- In order to get those examples in the computer, they'd need to (1) photograph and convert them into materials with not only color but specularity, roughness, displacement/normals (depth), and possibly subsurface scattering values, somehow modifying them to also get the right stylized looks and making them varied overall in the right ways (e.g. changing the scale size depending on flexibility), or (2) digitally paint the bitmaps for the aforementioned material properties (which, as you can imagine, may be time consuming and not easily tweaked, and in addition does not easily allow for crisp detail). Both of these methods are still used by other studios (and may be used sometimes by Pixar), especially for completely realistic materials or ones that are more stylized than Pixar usually makes. All three methods can also be combined.

Writing versatile software to generate materials allows materials in Pixar's style to be created faster and easier, to be more easily changed, and to be as minutely detailed and sharp as the artists want. In addition, animated effects are easier to achieve.

The examples in nature are still very important, and that's why shader packets are put together with such examples. Without real examples, the artists wouldn't know as well how to make something look natural.

If you'd like to see how materials are generated, you might want to look up tutorials or timelapses for Blender node editing and Substance Designer. Materials are made in these applications by linking together "nodes", each of which has a certain algorithm and has inputs and/or outputs.(1 vote)

## Video transcript

(clicking noise) - Good work! Now that we now how to
partition the space into cells, we can write a program to
do all the drawing for us. Plus my hand is getting tired! Then you'll love this program. It generates a uniform grid of sites, then it draws the resulting
Voronoi partition for us. That looks like a chess board. If we shift every other line of sites, we get this, like a beehive. Definitely getting us
closer to the dino scales. Notice it's following the Voronoi rules we saw
in the previous video. Any point you pick on these lines is equidistant to two or three of our sites. Okay, so how many sites do we need, and where do they go? Well, let's
check the shading packet. Our dino's
quite young, so she has relatively few scales on her legs. Perhaps five or seven would work. There are more
scales around the claws, but we can deal with that later. What's important is that the cells aren't all the same shape. Yes, we have a subtle variation in both cell size and shape, unlike the perfect honeycomb
our program is generating. - This is where the power
of random numbers comes in. - But applying randomness
in a way that makes organic look and variation
is really tricky. Look what happens when
we scatter the sites completely randomly and
then draw the lines. That doesn't look right. Way too clumpy. Yes, it's too random. We need more of a balance
between randomness and structure. I think a Poisson Disk
Process will work well here. It sounds fancy,
but it's quite simple. It uses a new parameter we can control, minimum site distance. We can visualize this as
a disk around each site. Think of this disk as the no drop zone. It works like this. A random site is generated,
then we generate another site anywhere outside the disc,
and we repeat this over and over until the plane is filled. Notice it's a smoother way
of distributing the points. There's much
less clumping happening now. Watch what happens
when we draw the partition. We get really close to the
geometry of the dino scales. - Beautiful! Okay, in the next exercise, you'll have a chance to
play with these ideas. - What was the most unexpected use of randomness you've encountered at Pixar? - I think the most surprising
thing about randomness is that it's really everywhere. Even in materials that you
might think are really constant, like metallic car paint or
brick work or something, let alone something like
human skin or dino skin. There's really randomness in every single material that we create. (gentle orchestral music) - Woah!