Interstellar movie black hole implemented with Einstein's equations in C++

https://twitter.com/bitfield/status/1020632237493112833

by sawirricardo • 2 years ago

139 106 2 years ago

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usrnm• 2 years ago

I wonder if people who wrote that code also consider their job boring and uninspiring

dvh• 2 years ago

Jeez not another stand-up on spaghettification before lunch!

KaiserPro6• 2 years ago

Standup! god I wish.

It'd more like a producer going:

"is it done yet?"

"what do you mean it'll take half our rendering budget, I need that for delivery"

"Is it done yet?"

"can you make it look more spacey?"

"no thats too spacey now"

"Why isnt there lens flare?"

"Why does it take two weeks to render, can't you fake it?"

gigatexal• 2 years ago

do you? sorry to hear that!

krona• 2 years ago

Perhaps they resented not being able to write it in MATLAB.

newswasboring• 2 years ago

Are you implying people like writing MATLAB? I've been writing MATLAB for about 10 years now, never once enjoyed it.

moomin• 2 years ago

They work in VFX, so their primary concerns are getting enough sleep and being able to pay rent.

zerr• 2 years ago

Repetitively translating existing formulas to code is not that satisfying.

mr_mitm• 2 years ago

Writing numerical solvers isn't that inspiring by itself to be honest. But I agree that the subject is fascinating. I suppose the code is not public so we could see ourselves, is it?

jebarker• 2 years ago

I don't understand the motivation for this comment, can you explain?

hermitcrab10• 2 years ago

It is a pity they didn't spend comparable effort on the story. I thought it was a really disappointing film, especially after they banged on so much about how good the physics in it was (apart from the black hole rendering, it wasn't).

guitarlimeo• 2 years ago

Did we watch the same movie? They got bunch of physics stuff right, like the water planet, the relative aging due to being near the massive black hole etc. Only thing that wasn't "correct" was the wormhole and especially the tesseract, but that was some creative writing which allowed for a nice twist. I enjoyed it, a nice scifi.

kawa• 2 years ago

Their starship was bullshit. On earth they needed a big Saturn 5 like rocket to bring it into space and later they fly into orbit like it's nothing.

If the planets they visited had much lower gravity then earth this may be possible, but this wasn't noticeable or talked about. And even on Mars you need much more fuel to get into orbit than could be stored in their tiny ship.

tambourine_man• 2 years ago

The whole premise is bogus and explained by Michael Caine in only a few sentences.

We have a plague on Earth and doing an interstellar travel is the solution?

I was very disappointed. I’m OK with a few plot holes, but this is so fundamental to the story that the movie can’t stand on its own.

bhickey2• 2 years ago

It was completely uneven.

Cooper sobbing as he listened to years of messages from his family? I wish I could've written that. The twist where Mann activated his beacon because he didn't want to die alone? Solid.

We need the gravity equation to get off Earth because the crops are dying? Love can escape a black hole through the tesseract? This is just patent technobabble nonsense.

Where _Interstellar_ fails is in exposition. Love is the most powerful force in the universe? The Fifth Element pulled that off by not pretending to be serious. Anything is permitted in science fiction, but once you commit to explaining it, you need to make sense.

anentropic• 2 years ago

100% agree, like you I was hyped after the pre-release teaser PR stuff came out about the realistic black hole rendering etc, was hoping for an actually decent sci-fi

and then just a lame story culminating in "space ghosts"

for me, arguably most disappointing movie ever

hermitcrab10• 2 years ago

Don't watch 'Ad Astra' then. That's also incredibly disappointing (IMHO).

throw3108223• 2 years ago

We're talking about a movie in which a space agency builds an enormous rocket entirely in secret and without any suppliers; then enrolls the astronaut at the head of the mission on the same day of the departure; and finally launches the rocket from inside its office halls. ¯\_(ツ)_/¯

https://www.youtube.com/watch?v=x9xFRch7N5o

actionfromafar3• 2 years ago

Well, if the launch fails, they won't need the office anymore. If the launch succeeds, same.

hermitcrab10• 2 years ago

It also hard to believe that being close enough to a giant black hole that it causes massive time dilation, doesn't seem to cause any other issues beyond large waves.

hermitcrab10• 2 years ago

They obviously used the same contractors that Bond villains use to build super bases inside volcanoes without anyone noticing.

VyseofArcadia• 2 years ago

Incredible soundtrack, though.

Qem• 2 years ago

Also the robots were cool.

bachmeier• 2 years ago

The title is basically nonsense. They're talking about the black hole in that movie.

kjrfghslkdjfl• 2 years ago

What did you expect from the title? That they used Einstein's equations to render the actors? Of course it's the black hole.

didgeoridoo2• 2 years ago

Since the digital movie camera used to film the actors relies on the photoelectric effect to turn light into pixel data, you could say Einstein’s equations were used for the live-action portion too!

antegamisou• 2 years ago

And it's not even Einstein's equations

     The geodesic equations are not Einstein's equations.
     The code for Interstellar only had to ray trace on a fixed analytical background spacetime (Kerr metric),
     rather than solve partial differential equations for the metric itself.

https://x.com/duetosymmetry/status/1020714102354776064

lmpdev• 2 years ago

Interstellar blackhole VFX implemented in 40k lines of C++

Would be a better title

sigmoid10• 2 years ago

Implemented using semi-realistic Einstein equations. They do talk about implementing a fully realistic version in the paper, but the director deemed it visually too confusing for the audience, so you only get to see a dumbed-down version in the movie.

fredski42• 2 years ago

Is there a visualization of the fully realistic version available somewhere?

indigoabstract2• 2 years ago

It's clickbait, but I'm amused since it implies the blackhole is the main star of the movie.

tgv• 2 years ago

Is it not? Would you say the Sun was the main star then?

NKosmatos• 2 years ago

If you want to avoid opening Twitter (now known as X), here is the link to the paper: https://arxiv.org/pdf/1502.03808

TLDR “A typical IMAX image has 23 million pixels, and for Interstellar we had to generate many thousand images, so DNGR had to be very efficient. It has 40,000 lines of C++ code and runs across Double Negative’s Linux-based render-farm. Depending on the degree of gravitational lensing in an image, it typically takes from 30 minutes to several hours running on 10 CPU cores to create a single IMAX image. Our London render-farm comprises 1633 Dell-M620 blade servers; each blade has two 10-core E5-2680 Intel Xeon CPUs with 156GB RAM. During production of Interstellar, several hundred of these were typically being used by our DNGR code.“

slig2• 2 years ago

How fast could this run in a modern CPU with a modern GPU?

jsheard3• 2 years ago

GPUs are almost irrelevant for VFX work at this scale due to the memory requirements. The render nodes used for Interstellar had 156GB of RAM, and a decade later the biggest GPUs still don't have that much memory (unless you count Macs I suppose but the existing software ecosystem is very CUDA-centric).

Small VFX shops do typically render on GPUs nowadays, but the high end is still dominated by CPU rendering.

KaiserPro6• 2 years ago

Its a particle simulation, so a lot of it is memory management.

I can't remember the actual size of the simulation in terms of number of particles, but it was using something like 2 150TB fileservers to store it on.

With NVME and cheap ram, it would probably at the point where it'd be useful on a GPU.

0xf00ff00f• 2 years ago

There's a nice recreation on Shadertoy:

https://www.shadertoy.com/view/lstSRS

No idea if it's doing the same simulation though.

ginko• 2 years ago

There was a pretty good talk[1] on this at SIGGRAPH 2015. Speakers included later Nobel prize winner Kip Thorne. I tried to find any recordings but had no luck. (Presumably it's on the conference DVD)

[1] https://history.siggraph.org/learning/double-negative-presen...

idk1• 2 years ago

[possible spoiler alert]

Is Intersetllar the movie where Matthew McConaughey turned into a bookcase?

Waterluvian• 2 years ago

It’s the one where Matt Damon gets stuck on another planet.

No not that one.

Not that one either.

fouronnes3• 2 years ago

New Fermi estimation interview question just dropped: are there more movies where Matt Damon is stuck on a planet, or movies where Tom Hanks plays a captain?

ane• 2 years ago

Is the third movie supposed to be Elysium?

danielbln• 2 years ago

He didn't turn into a book case, but a book case as a sort of representation of multi dimensional space was a part of the movie, yes.

cossatot• 2 years ago

And the infinite book case is a shout out to Borges, right?

ropejumper• 2 years ago

Not turned into, he got put into a projection of a higher-dimensional space at the location of his daughter's bookcase some time in the past.

jbverschoor• 2 years ago

Hilarious

manuelmoreale• 2 years ago

There’s an interesting discussion related to this in this video: https://youtube.com/watch?v=Z4oy6mnkyW4

mode80• 2 years ago

ScienceClic did an excellent video about the accuracy with a better recreation: https://youtu.be/ABFGKdKKKyg

KaiserPro6• 2 years ago

I worked on this movie, I was at DNEG at the time. One of the standout things that I remember is that this particular simulation was toxic to the fileserver that it was being stored on.

From what I recall, I don't think that it was running on that many machines at once. Mainly because it required the high memory nodes that were expensive. I think it was only running on ~10 possibly 50 machines concurrently. But I could be wrong.

What it did have was at least one dedicated fileserver though. Each of the file servers at the time were some dual proc dell 1u thing with as much ram as you could stuff in them at the time (384 gigs I think). They were attached by SAS to a single 60 drive 4u raid array. (Dell PowerVault MD3460 or something along those lines. They are rebadged by Dell and were the first practical hotswap enclosure that took normal 3.5" SAS drives, that didn't cost the earth)

The array was formatted into 4 raid6 groups, and LVM'd together on the server. it was then shared out by NFS over bonded 10gig links.

Anyway. That simulation totally fucked the disks in the array. By the time it finished (I think it was a 2 week run time) it had eaten something like 14 hard drives. Every time a new disk was inserted, another would start to fail. It was so close to fucking up the whole time.

I had thought that the simulation was a plugin for houdini, or one of the other fluid simulation engines we had kicking around, rather than a custom 40k C++ program.

greggsy2• 2 years ago

The paper mentions that the accretion disc was rendered in Houdini.

It also mentions that ‘several hundred’ of their 1633 10-core, 156GB (weird number?) blade servers were used, but didn’t seem to go into details on data storage.

Is it possible you were working at the compositing phase, which would have been very heavy on random read and writes, resulting in more wear on the disks?

KaiserPro6• 2 years ago

you were working at the compositing phase,

I was a systems engineer at the time. Compositing is actually really quite ideal linear streaming. You read the images serially and tend to write them back serially. which for spinny hard disks is about as optimal as possible. each frame tends to be between 20-150 megs (resolution, layers, bitdepth). but they are rarely read in a random IO way, you start at frame 1 and go to frame

there were 32 primary fileservers at the time, two were spare, and, including the nearlines (which were _n_ lustre machines and each had 4 raid arrays attached by SAS rather than one) we'd normally expected to replace twoish disks a week.

They ran particle sims all the time. Water, smoke, explosions are all staples of VFX. It was just something weird about this particular sim.

My understanding was that the actual simulation was causing the disks to die, rather than the render. A render can be restarted, a sim, less so. Well, this sim at least.

FrustratedMonky• 2 years ago

Is it just so much read/write? I'm having hard time understanding why a simulation would need so much read/write to disk? Wouldn't the CPU and RAM be more important for calculations, then write them to disk when done?

greggsy2• 2 years ago

I was thinking the same. It took 30 minutes to ‘several hours’ to produce 23 megapixel renders, which are 100MB max.

Either the renders were heavily paging memory to disk, or OP was working at the compositing phase.

KaiserPro6• 2 years ago

TLDR: the number of particles used, and the memory required was far too big to fit on one machine. more over, machines needed to pass data to each other, they chose to use files for that.

Long story:

Forgive me if you already know this, I'm going to start with a toy example and then ramp up the scale.

Imagine that you are doing a "normal" simulation of something like a ball rolling down a ramp into a pot. That's fairly simple, but you need to know the position of the ball, the force vector and the location of any object near by that might collide with it.

It gets a bit harder when there are two balls, as they might also interact, so you need to store the state of two balls.

At a thousand balls, you start to need to think about scaling/threading/parralising (I mean you probably don't, you'd just use physX from nvidia and make it the library's problem, but bear with me) One way is to divide up the simulation area into a bunch of voxels and treat them as individual processing areas. When an object enters/exits an simulation area, you pass the object over with its force vector, and mass, and let that simulator deal with it.

Now, I'm not a physics engine person. The above may or may not happen as I describe, but the key thing is, there are sub simulation to allow you to run in parallel. You need to make sure that each processing voxel has completed it's processing for that time step before you can move on.

Once you have calcuated the position of each object, you can save that to disk and begin to calculate the next frame. Note, this isn't rendering, this is just working out the "pose" (position and rotation) of each active object.

The simulation of the black hole was effectively a massive particle simulation. I don't recall how many particles, but something like 14 billion sticks in my mind. It might have only been a billion. So they need to calculate and store the id, position, rotation, velocity and probably other details for every single particle. Even if everything is in a single float for a billion particles, its 28 gigabytes for position and rotation alone (xyz for position, quaternion for rotation) That's without any other state info like heat, force vectors, the weird quantum stuff or weight.

Once you have the position of all the particles, you then need to fire photons through them to work out what colour the pixel should be. That involves loading in the position of the particles, firing rays through them all and recording what it hits and why.

But why so much file IO? didn't the machines talk directly?

DNEG at the time was as close to being a "perfect" unix/linux shop as you could get. everything was ephemeral, even the file servers. All the nodes in the render farm could configure themselves from scratch (pretty much) from power on. You'd plug it in, switch it on and it would work out what it's hostname is, image themselves and join the rendering system autonomously. Most binaries that you used were stored on an NFS share somewhere. this meant that you had more or less complete control over the data flow. For example `rm` wasn't actually rm, it was a wrapper that moved files into a 'deleted' area, rather than binning them.

There were many layers of backup, all the way to tape.

Your home directory followed you everywhere, which meant so did your environment. This meant that if you wanted a specific version of a program, we had a wrapper that set that for you. So typing "maya" would spin up the right version of maya, use the correct plugins, and safe your files to the correct fileserver.

Everything was divided into shows. so you'd cd /shows/$showname/$department/$shotnumber/$version and you'd magically be on the right fileserver. This was done via the magic of symlinks.

So everything was files, and if you wanted to exchange large amounts of data, you'd use files.

If anyone is interested I'll talk about the system they used to coordinate all the rendering (no it wasn't k8s)

mike5032• 2 years ago

Thank you for working on this movie :)

tempoponet• 2 years ago

a 32,000-core render farm at about 20 core-hours per frame

~26 2/3 frames per minute, not bad

sidcool• 2 years ago

This movie gives me chills everytime I see it. The attention to detail is immaculate.

DerekL• 2 years ago

Title is misspelled, should be “black hole” (two words).

dang• 2 years ago

O K. Thanks!

joelwallis• 2 years ago

I could do it with Photoshop, two candles of Red Bull and a 5K USD payment in my account.

Jokes apart — this is the best SciFi movie ever! It’ll become one of these movies one’s got to rewatch every 5y or so.

mike5032• 2 years ago

I watch it multiple times a year :)

Interstellar movie black hole implemented with Einstein's equations in C++

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