State-of-the-art 3D rendering involves bouncing light rays through a scene to capture color and texture with an amazingly simple algorithm called path tracing. In this tutorial session, Hunter will render beautiful images by tracing the paths of billions of photons with Go on cheap cloud hardware.

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Painting with Light
GopherCon 2018

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1940s: The Manhattan Project

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"Monte Carlo Integration"

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1986: Kajiya's rendering equation

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1986: Kajiya's rendering equation
$44,000,000 / GFLOPS

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1995: Toy Story

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“There are more PhDs working on
this film than any other in movie
history.”
- Steve Jobs, Pixar, 1995

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-$30,000,000

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-$30,000,000
+$364,545,516

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-$30,000,000
+$364,545,516
$46,000 / GFLOPS

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2006: Monster House

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2006: Monster House
$57 / GFLOPS

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2014: Big Hero 6

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2014: Big Hero 6
$0.13 / GFLOPS

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4 render farms

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4 render farms
4,600 servers

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4 render farms
4,600 servers
83 hrs / frame

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2016: Deadpool

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2016: Path-tracing only

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2016: Path-tracing only
$0.08 / GFLOPS

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v0.0.1

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2 obstacles...

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JavaScript!

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...time to learn Go!

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$ heroku scale worker=1
(1.6 million surfaces!)

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$ heroku scale worker=10
("embarrassingly parallel")

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Building a path tracer with Go

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Building a path tracer with Go
In plain English

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Building a path tracer with Go
In plain English
...with as little math as possible

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Building a path tracer with Go
In plain English
...with as little math as possible
...and just a touch of physics.

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What is light?

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origin

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origin
direction

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origin
direction
energy (RGB)

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Origin + Direction + Energy

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What happens when light hits a
surface?

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Reflection

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Reflection
Refraction

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"conductors"

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"dielectrics"

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transmittance diffusion
Once refracted, light is either transmitted or
diffused

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All incoming light is either...
3. transmitted
1. reflected
2. diffused

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How can we simulate these
three behaviors with Go?
3. transmitted
1. reflected
2. diffused

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BRDFs and BTDFs!
"Bidirectional Reflectance Distribution Function"
"Bidirectional Transmittance Distribution Function"

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BRDFs and BTDFs!
"Bidirectional Reflectance Distribution Function"
"Bidirectional Transmittance Distribution Function"

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A pure function that describes a material

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A pure function that describes a material

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A pure function that describes a material

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The physics have been done for us!
Metals
microfacet BRDF
Non-metals
microfacet + Oren-Nayar BRDFs
Transparent materials
microfacet BTDF + Beer's law
...car paint, hair, thin films, clouds, skin...

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But... that's just one random path!

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But... that's just one random path!

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“Monte Carlo integration”

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“Monte Carlo integration”

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“Monte Carlo integration”
Sample a bunch of values randomly.

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“Monte Carlo integration”
Sample a bunch of values randomly.
Add them all up and average them.

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“Monte Carlo integration”
Sample a bunch of values randomly.
Add them all up and average them.
That’s probably close to the real answer.

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Path tracing + Monte Carlo integration
rendered with github.com/hunterloftis/pbr

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Path tracing + Monte Carlo integration
rendered with github.com/hunterloftis/pbr

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Path tracing + Monte Carlo integration
rendered with github.com/hunterloftis/pbr

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15x improvement over JS!
rendered with github.com/hunterloftis/pbr

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How can we make
more interesting images?

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Complex geometry
rendered with github.com/hunterloftis/pbr

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Complex geometry
rendered with github.com/hunterloftis/pbr

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Complex geometry
rendered with github.com/hunterloftis/pbr

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Complex geometry
rendered with github.com/hunterloftis/pbr

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Complex geometry
rendered with github.com/hunterloftis/pbr

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Real materials
rendered with github.com/hunterloftis/pbr

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Real materials
rendered with github.com/hunterloftis/pbr

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Real materials
rendered with github.com/hunterloftis/pbr

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Real materials
rendered with github.com/hunterloftis/pbr

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Image-based lighting
rendered with github.com/hunterloftis/pbr

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Image-based lighting
rendered with github.com/hunterloftis/pbr

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Image-based lighting
rendered with github.com/hunterloftis/pbr

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Image-based lighting
rendered with github.com/hunterloftis/pbr

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💡moments with Go

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"direction = 2 meters up + a halogen light bulb"

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"direction = 2 meters up + a halogen light bulb"
"position = fuchsia turned 90 degrees"

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type define

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type define

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“Parallelization can fall out
[from concurrent design].”
- Rob Pike, Heroku Waza Conf, 2012

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“Goroutines aren't free, but they're
very cheap.”
- Rob Pike, Heroku Waza Conf, 2012

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Parallelization can fall out... but it
might not run fast.

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Parallelization can fall out... but it
might not run fast.
Goroutines are very cheap... but
communicating between them is
expensive.

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The Future

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2018

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2018

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2018

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2018

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2018

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An exciting, emerging field
Research that hasn't been implemented yet
"Embarrassingly parallel" algorithm
Fun to hack on!

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I would love your help!

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How's our doing?

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Thank you!
https://github.com/hunterloftis/pbr
https://www.chemie.unibas.ch/~steinhauser/teaching/FS2014/MD-Simulation/Handout_17.pdf
https://www.disneyanimation.com/technology/innovations/hyperion
http://www.cse.chalmers.se/edu/year/2013/course/TDA361/Pathtracing.pdf
http://blog.selfshadow.com/publications/s2015-shading-course/hoffman/s2015_pbs_physics_math_slides.pdf
https://www.cs.cmu.edu/afs/cs/academic/class/15462-f09/www/lec/lec8.pdf
https://www.atomicheritage.org/history/computing-and-manhattan-project
https://graphics.pixar.com/library/PathTracedMovies/paper.pdf
https://www.wired.com/1995/12/toy-story/
https://en.wikipedia.org/wiki/FLOPS#Cost_of_computing
Hunter@Heroku.com