
The Tech of Pixar: Piper (2017) - gdubs
https://www.fxguide.com/fxfeatured/the-tech-of-pixar-part-1-piper-daring-to-be-different/
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Animats
The approach is straightforward. "Every shot in Piper is composed of millions
of grains of sand, each one of them around 5000 polygons." With enough compute
power, you don't have to fake as much.

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Joeboy
Unless you're looking at it very, very closely, does 5k polygon sand look any
different from 500 polygon sand, or even 50 polygon sand? Even the very close
ups in the article look like they'd be much the same with a lot fewer
polygons.

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have_faith
That was my first question. They mention in the article the high number is for
close ups.

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Joeboy
Also says:

> Every shot in Piper is composed of millions of grains of

> sand, each one of them around 5000 polygons.

I'm guessing the article is just confused. The important point, I think, is
about using real geometry for sand particles rather than the beach being a
surface with a displacement map.

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jobigoud
But with instancing. So they could have a few dozens of grain types 5K tris
each and the total number is from instances, no need to load 5 billion
triangles into memory.

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mschaef
What does that look like from a data structure perspective? Each grain has a
bounding box and you only look at the geometry for that grain if a ray crosses
the box? (I'm way, way out of my wheelhouse here, if it's not already
obvious.)

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w0utert
Reduced ad absurdum I thinks that is pretty much how it works. There is an
acceleration structure that is traversed for each ray, to reduce the search
space for ray-geometry intersections (probably a bounding volume hierarchy of
some sorts), and using instancing only a very small subset of the total of all
grains of sand actually need to be stored and processed. I imagine the sand is
modeled using some particle system where each particle is actually a small
scene of sand grain models in itself, with its own BVH etc, and the raytracer
somehow reuses whatever happens inside them for every other particle that has
the same lighting conditions.

It’s probably way way more complicated than that though. Extremely interesting
stuff.

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froindt
I saw this when I saw Finding Dory. The sea foam was _so_ good! I geek out
about digital animation and was absolutely blown away.

I'm not ashamed to admit I teared up a bit at how good it was.

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Angostura
I thought the sea in Moana was even better.

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froindt
I'm very much behind on movies. It's on my list though.

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Operyl
This trailer[0] has a few shots of the sea.

[0]
[https://www.youtube.com/watch?v=LKFuXETZUsI](https://www.youtube.com/watch?v=LKFuXETZUsI)

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wmertens
This was a fascinating and humbling read, and only after reading did I realize
this was almost 3 years old… What are they animating now? Snowstorms with
individual unique flakes?

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fenwick67
They already generated ~2000 different flakes and a snow simulation system for
Frozen.

[https://en.wikipedia.org/wiki/Frozen_(2013_film)#Technology_...](https://en.wikipedia.org/wiki/Frozen_\(2013_film\)#Technology_development)

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spongeb00b
This is absolutely amazing. When I first saw Piper I assumed they were cutting
real video of the water and beach is was just so realistic.

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knolan
The article makes the point that it became inefficient to use displacement
maps due to their size ballooning beyond '36 times' what they would normally
use. So this means that the ground displacement map was just not detailed
enough and pushing it to higher resolutions didn't scale. Instead they used
Houdini to generate sand grains, I presume Houdini used some sort of
displacement map per grain? The final result is a mesh nevertheless.

They also mention that, "this result was driven by a combination of culling
techniques including camera frustum, facing angles and distance, creating a
variance of dense to coarse patches of sand for optimum efficiency."

So while they had grains each of ~5000 polygons available to them and
positions that they could occupy, they cut down on that polygon count using a
combination of techniques (many common in games too) to make it all work. So
the polygons of any grains outside the camera frustum were ignored. The faces
of the grains point away from, I presume, any light source and therefor not
contributing to the path tracer were ignored and also some soft of LOD to
reduce polygon count as distance.

As an amateur blender user I'm reminded of microdisplacement as a way for us
mere mortals to achieve something in this space:
[https://www.blenderguru.com/tutorials/introduction-
microdisp...](https://www.blenderguru.com/tutorials/introduction-
microdisplacements)

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willis936
Doesn’t aggressive culling present issues with ray traced lighting? If you
remove an umbrella that’s behind the frustum then a shadow in the scene is
missing. Even harder is if you cull a second layer of sand grains then you
don’t get the light that reflects off of them (assuming partial transparency
of grains).

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knolan
Yes, so I presume they only remove the faces that are not exposed to any light
bounce.

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macintux
2017.

Didn’t understand most of it, but it is a jaw-droppingly beautiful short, and
the stills in the article are well worth the skim.

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joezydeco
Pixar shorts have always been test beds for techniques and technologies that
show up in their feature films in the years afterward.

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berkut
Indeed. And rumour is they've stopped doing them now.

On the VFX side of the industry we were often jealous of Pixar and Dreamworks
being able to do shorts, in terms of having the scope and ability to test out
new tech / pipelines.

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KaiserPro
Yeah, but then you realised why they were doing them, because they were using
their own in-house tools.

Pixar was the last holdout for maya, they only converted in the last few years

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ahaferburg
Are you saying that Pixar is using Maya now? For which parts of the workflow?

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hathym
Remind me of this [https://empwaynek.files.wordpress.com/2014/01/draw-an-
owl.pn...](https://empwaynek.files.wordpress.com/2014/01/draw-an-owl.png)

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mroche
Don't forget Part 2: Finding Dory - making waves

[https://www.fxguide.com/fxfeatured/the-tech-of-pixar-
part-2-...](https://www.fxguide.com/fxfeatured/the-tech-of-pixar-
part-2-finding-dory-making-waves/)

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zuhayeer
After a certain threshold of processing power, you can just use earth as it
is, pretty amazing

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knodi123
After a certain threshold, earth as it is can be seen as a tool for powerful
processing. At least, that's what a little white mouse told me.

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unnouinceput
And this was 2017! Imagine what Pixar have in stores now. I, for one, can't
wait to see what they come up with next, in term of shorts I mean.

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milleramp
Is there a HDR render of this available?

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thomasjudge
Is the beach shared somehow shot to shot? Is there a database storing each
sand grain?

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anibalin
The sand is mind blowing. Every grain is a mesh itself.

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Gravityloss
But what about the plastic?

