Pixar in a Box – Khan Academy

by beneater • 11 years ago

753 65 11 years ago

britcruise4• 11 years ago

Hey HN! My name is Brit Cruise and I'm the lead content developer on the Khan Academy side of this equation (working alongside Tony DeRose from Pixar...plus a village of others), if you have any specific questions about this project I'll be happy to answer as best I can.

spb• 11 years ago

Looks pretty interesting. Was the domain for the content a Khan Academy decision, or was that just personal prerogative?

britcruise4• 11 years ago

The initial idea for this content came from Pixar (Tony DeRose had given talks in the past showing connections between math and the movies - see here a video he did with numberphile a while back: https://www.youtube.com/watch?v=2NzTAaYgk4Q). The goal was to turn that sort of thing into a series of interactive lessons.

drewblaisdell• 11 years ago

Not a comment about this specifically, but I'm a big fan of your other courses on Khan Academy. They changed the way I think about the world. I can't overstate how grateful I am that you created them.

Everyone should check out these lessons:

Journey into cryptography: https://www.khanacademy.org/computing/computer-science/crypt...

Journey into information theory: https://www.khanacademy.org/computing/computer-science/infor...

merpnderp2• 11 years ago

I can't believe you just posted this. I had a 5 hour drive this morning and listened to nearly all the cryptography lectures during it.

Yhippa• 11 years ago

These videos were the main reason I grokked Diffie-Hellman during my grad CS course in crypto last year. Those are very good resources!

Paul_S• 11 years ago

I'm trying out different videos and I can't find ANY instructional content in them - I mean in terms of technical information, something applied that you can learn and use. It feels like watching a TED talk and not a Khan academy lecture!

wbhart2• 11 years ago

I just watched the first two sequences of videos and so far they have shown how to compute midpoints of lines and how to compute the coordinates of points on parabolic arcs given three arbitrary control points, including how to prove the identities involved. They then explain how this is used in practice to generate the shape of a blade of grass. Is this not the kind of technical information you were expecting to find?

tinco• 11 years ago

I love Khan Academy, I used it extensively to practice calculus and I think also discrete mathematics back in college.

I just watched the videos of the first few sections of this math course and they're all very nice and I feel I really understand how to draw parabolas now, but the section I just watched ends with a proof.

I'm not convinced by the proof at all, it goes very fast through the basics and is very quick to point out the different relations between the ratios and the points. Now I know I've never been very quick with proofs, and I know the whole idea of Khan Academy is that you can pause and replay whenever you like, but I feel just a video isn't enough to explain even a simple geometric proof like this. Did you test this on any students? Could they reproduce the proof?

(p.s.: many events cause a bar to appear on the top of the page that pushes the entire page down, that's very not-done in web ux and causes disorientation and frustration with the user especially if the site is slow to respond (which the site is for me))

wbhart2• 11 years ago

The proof starts with two of the "string-art" lines, a line L1 (line Q'R' in the video) with parameter s and a line L2 (line QR in the video) with parameter t, and computes the intersection point P of these two lines. Keeping line L2 fixed, one gets a series of intersection points P as one varies the parameter s. One then notices that the point of intersection of line L2 and the parabola (the "touching point") is the limit of these intersection points P as s tends toward the value t. The proof finishes by showing that this limit point is just what it was hypothesised to be, namely the point along line L2 that divides it in the same proportions as its endpoints divide the control lines.

I agree that some students will not recognise the crux of the proof, but will simply see something ends up being equal to something else in some identity without understanding how that relates to what was being proved.

Euclid's Elements (an ancient Greek textbook on Geometry) is a good model in this regard. He first states what he is to prove. He then starts from the assumptions and finishes with what he was to prove. Each step in between is justified.

VikingCoder• 11 years ago

I've been lucky to see Tony DeRose, Alvy Ray Smith, and a few others give presentations in small, intimate settings at my local University.

Is there some way we could please SUBSCRIBE to notifications that wonderful speakers like these are coming to our area?

Okay, yes, I know this isn't your job, but please... you might be able to help me! :)

thespace123• 11 years ago

Are you going to add this content to your iOS app? Also my friend is looking forward to that Android app!!

andymatuschak• 11 years ago

The non-interactive content should mostly work in the iPad app. iPhone is trickier.

This is a tough area for us in general, unfortunately.

Keyframe4• 11 years ago

There is an undergrad (I think it's an undergrad) course on Ray Tracing for Global Illumination here https://www.youtube.com/playlist?list=PLslgisHe5tBPckSYyKoU3...

I've written an RSL tutorial that has been online for past 15 years (it's currently offline, I'll put it up again) and I've had people from all over the world from different studios (big and small) thank me.. it seems RSL doesn't have much resources online and considering this is tied to Pixar - do you have plans for RSL?

tomvbussel5• 11 years ago

The CG by UC Berkeley on EdX is a great starting point. One of the exercises involves building a simple ray tracer. A slightly more advanced source on ray tracing is http://www.scratchapixel.com/. Of course the best way to learn about ray tracing is by reading Physically Based Rendering: From Theory to Implementation by Pharr and Humphreys.

Pixar has ditched RSL in favor of BSDFs written in C++, so there is no real reason for learning RSL anymore. Open Shading Language (OSL) is a new shading language which is getting more and more use in the industry, but it's completely different by design.

Grantarvey• 11 years ago

This is such an awesome resource!!!! {Edit: I say this as a writer and not as a 3D animator / designer. I apologize for sounding very fan-boy about it, but I do really appreciate this.}

adsfasdf23f23f• 11 years ago

Some text indicating the target audience and any prerequisite knowledge would be great.

jameshart• 11 years ago

Love this. So important to show kids that there really are applications for the stuff they are learning in math classes, and computer graphics are such a direct way to see that connection. As a kid, I think the main reasons I cared about things like equations of motion or trigonometric functions were because I was using them to do stuff like animate bouncing balls.

ginko• 11 years ago

It's interesting that the Rendering chapter only covers ray tracing, while most classic Pixar movies were actually mainly rendered using the Reyes algorithm, which is a form of rasterization.

ska3• 11 years ago

Isn't Reyes essentially a speed hack [1]? As so, is it particularly relevant to learn about today in introductory material?

[1] by which i mean, inferior estimation of BSDF on/in model, but much much faster.

tomvbussel5• 11 years ago

The REYES algorithm is an algorithm that can very quickly produce batches of shading points (with the required information to shade them such as the viewing direction). It's not really a hack and you can still use path tracing (with BSDFs) to correctly shade these points. In fact this is what Pixar did for Monster's University; they used the REYES algorithm to determine shading points visible from the camera and then shaded those using BSDFs and path tracing. The problem with this is that you basically have to store the scene twice: once for rasterization and once for ray tracing.

sitkack• 11 years ago

I think it is important to know what the trade offs are in terms of speed, cost, quality. Lots of children's TV programs look like they are rendered with Unity or worse. Most likely on a single machine in real time.

tbabb3• 11 years ago

Pixar movies from Finding Dory onward will be exclusively raytracing, FWIW.

wyldfire• 11 years ago

You sound pretty authoritative here, so I'll ask a semi-topical question: are the creative teams the ones driving this kind of development? "We need better fidelity/IQ because I would like this film to look more impressive that previous ones." Or is it more along the lines of Pixar demonstrating industry leadership?

Keyframe4• 11 years ago

REYES is now one of in newer PRMans for quite some time.

harywilke• 11 years ago

REYES (Render Everything You've Ever Seen) has been the basis of PRMan since the start. Recently PRMan has shifted away from this approach and towards more ray tracing. see the following for descriptions of REYES: http://renderman.pixar.com/view/reyes-renderman-under-the-ho... or the 1987 paper by Cook, Carpenter and Catmul http://graphics.pixar.com/library/Reyes/paper.pdf

pcote• 11 years ago

I think the name "Pixar in a Box" sounds like a neat play on words on the term "Particle in a Box" from quantum mechanics. Sometimes, it's called an "infinite potential well".

So the title appears to come from the suggestion that there'a a well of infinite potential in terms of creative usages of math in computer animation. Or at least that's what I read into it.

ChicagoBoy11• 11 years ago

Wonderful initiative -- wish this was around when I was in school.

Any projects in the works to tie this into Khan Academy's CS offerings? I work at a school which is about to pilot a programming class with 3d animation, but I found the content which you guys have put up to be far more engaging. If there were an accompanying suite where students could code and render an entire scene (especially if some Pixar assets were included!) it would absolutely be incredible and a great resource, and I certainly wouldn't hesitate one second to transition our course into it.

pamelafox• 11 years ago

I'm Pamela, the programming teacher for KA. We're thinking about adding highly guided coding challenges to the PIAB content in the future, to entice students to go deeper into programming. Alternately, we could add advanced coding challenges that have a higher prereq. We haven't quite figured out the approach yet (and that applies generally to introducing programming to other areas of KA). Feel free to email compsci-feedback@khanacademy.org with your thoughts. :)

ausjke• 11 years ago

Love Khanacademy, I wish I can bookmark course like this for later viewing, could not figure out how to do that yet. I'm a coach there but like to bookmark course for myself once a while.

prezjordan• 11 years ago

Start watching some content and it'll appear on your homepage next time you visit :)

anjc2• 11 years ago

It's odd that people in the comments seem to think this is for kids. It surely isn't intended to be for children, right?

Great lessons.

tomvbussel5• 11 years ago

I think this is aimed at middle/high school students. It probably can be interesting for adults, but I'd really recommend picking up a book such as Fundamentals of Computer Graphics by Shirley and Marschner [1].

[1] https://www.cs.cornell.edu/~srm/fcg3/

anjc2• 11 years ago

Yeah it seems to be aimed at teens, but this is so far beyond most excellent high school students. They're dropping in terms and concepts which you don't touch on until the final years in an undergrad, with a focus on graphics.

gdubs• 11 years ago

I brought a computer graphics textbook into my high-school math class and asked my teacher if he could help me figure it out. His response was that I needed to pay attention to the current lesson plan, and would need to get through trig, then calculus before we could approach the book.

What's amazing about this video series is that they have actually captured the elements that _can_ be taught to kids of various ages and skill levels. Man how I wish there were a resource like this when I was younger.

dman• 11 years ago

You are younger than you will be two years from now.

hueving• 11 years ago

Not relevant to what happened to him in high school.

Animats• 11 years ago

That reflects a high school math teacher view.

To understand basic 3D computer graphics, you need some linear algebra, matrices, some analytic geometry, and some trigonometry, but not much calculus. Once you learn what a 4x4 matrix multiply can do, you have most of the key ideas. You need that to use OpenGL effectively. Actually, you only need about 10% of each of those areas of math, but you do need that 10%. "Graphics Gems" has some good background.

(Physics engines, though... I used to work on that, and struggled through two-volume books on nonlinear differential equations.)

kragen• 11 years ago

Your teacher was a fucking idiot. What was his name, and what city does he live in?

danielrw7• 11 years ago

FYI the image formatting is off on mobile chrome. http://imgur.com/0dyvQJP

JabavuAdams• 11 years ago

Nice! I was just thinking about using CG as an enticement to teach linear algebra. Basically, turn the curriculum upside down: here's how you rotate an object ... a point is a vector .... here's a matrix ...

That's how I learned it.

anderspitman• 11 years ago

Khan Academy got me through calc III and diff Eq

Pixar in a Box – Khan Academy

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