VFX Artist Explains the HARDEST Visual Effect to Make

Imagine that the reason for "Avatar: The Way of Water" to have taken so many years to be released was due to the caustics finally finished rendering.

I always loved seeing the ins and outs of VFX, it's a perfect example of "if you do things right, people won't be sure you've done anything at all."

Just watched avatar the way of water and it’s definitely simulated. The light patterns changes accurately when a creature is disturbing the water surface. It’s crazy how good it looks.

These Wren videos are some of the highest quality videos out there. His understanding and ability to explain these concepts is so unreal. Great stuff!

it's a shame to come back to a video i used to enjoy, now knowing this company is so comfortable with art theft and is even complicit in it.

"Real life runs constantly in real time without ever crashing." Well, I would certainly hope so. Great video Wren.

omg I cant believe mark is actually doing normal stuff for the channel this is so cool. this just made corridor crew 10x better.

I think the main case where simulated caustics for an underwater shot would be more notably different than the gobo option, is when the thing catching the caustics is very close to the surface of the water. The parts of the dinosaur that are right up against the water would catch very different caustics than the parts further away, not just in brightness but in sharpness as well. If you move the dinosaur further underwater, the difference between the close parts and the far parts becomes less significant, and the result looks a lot more like the gobo.

The history of long hair in animated movies. Simulating hair has been such an interesting subject. I think it would make a pretty good video.

Man I missed Wren's deep-dives into very specific topics. I enjoy most of the content on this channel, but those hit particularly hard for me since he usually does either a science-y topic, or something crazy and obsessive about a sci-fi franchise... in either case, I love the effort you (Wren + the whole team involved) put into these vids.

As far as I'm concerned I saw the trailer of Avatar the way of water multiple times and each time I caught some new details but talking about Caustics, yes they were both a mixture of original shots under water and perfect cgi because one can clearly see the rays of light in the trailer but that doesn't happen in real life and the Caustics get dull as depth increases also the clarity of water is the biggest factor in play here, cleaner the water more crisp are the Caustics

I've always simulated water wave caustics simply by using a Voronoi noise shader in World space under a Colorizer filter in the Luminance channel. The gradient of the colorizer is then mapped to an inverse-square falloff (I use a Python node to generate the gradient knots from a formula) to give it the sharp contrast between the bright thin regions and dim falloff characteristic of these kinds of caustics. It looks very close to real, and adds zero to the render time.

When you consider if someone were to actually run that 11 year render, by the time it finishes you would probably be able to run an equivalent render in an hour with the advances in both hardware and render algorithms, probably also with some sort of AI enhancement thrown in.

Wren : finds an amazing shot Wren a few minutes later: realizes the shot was simpler than imagined Also Wren : fuck it, I wanna try the hard way and see it's worth it And that's why we love this channel

I think the gobo shot can be improved just by altering the actual video used for the light. So if you want to change the light falloff, you could try and change the light gradients and shapes, and adjust the intensity and contrast of the light source.

I was working on that in uni decades ago. The reason caustics are hard is there's no obvious way to trace a path from the camera to the light through 3rd surfaces. Normally you trace from camera to surface and then you trace in the direction of each light to see if the patch of surface is illuminated. But if light is to come through reflection or refraction it could be coming through any path. You'd have to render the entire scene from the PoV each surface patch just to calculate 2nd level lighting. Or you could trace photons forward from the light, have them deposit on surfaces randomly like textures, and then trace the scene from the camera and hope you got enough photons. That's the slow technique that I worked on way back. You could do better with fancy sampling and compression of photons, or some differential approximation of path tracing, which I'm guessing form part of the new renderer.

Wow I can't believe wren was able to speak under water so clearly!!! Fantastic job!

Wren is honestly a great educator. Has a passionate energy, knowledgeable background, and ability to simplify complicated ideas. He really could have his own education channel and I bet it'd be huge!

I find it interesting that caustic filters of animation and film is like the filtering of convolution reverb on audio. You can take the room sound reflection response of something and put it on audio to simulate that a recording is taking place in a specific place like a bathroom or a tunnel.

Congratulations, Wren. I think this is the best video you've ever done. Well done, you did a great job putting this together <33