Weta Digital on how they made those raging rapids in ‘Jungle Cruise’

Water sims, CG environments…and lots of bubbles.

At one point in Jungle Cruise, the characters played by Dwayne Johnson, Emily Blunt and Jack Whitehall venture down the Amazon River where they hit some significant rapids and almost go over a waterfall.

Tasked with the visual effects for the exciting rapids sequence was Weta Digital. Here, Weta’s visual effects supervisor Luke Millar, who worked with production VFX supes Jake Morrison and Jim Berney, breaks down how the shots featuring water sims, CG jungle and boat plates were realized.

b&a: What were the things story-wise that you knew you had to solve in terms of the look and feel of water for the rapids sequence?

Luke Millar: The big trick with that was the art direct-ability of the boat, the speed of which you went through the rapids and what kind of splashes it made. I think with a sequence like that, it’s so heavily buried in physics. And if you start to try and cheat those physics, which is what happens a lot of the time, then the simulation stuff all goes right out the window, and it breaks everything.

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One of the trickiest things with water in particular is that it scales terribly. So you have to nail the scale. We did a lot of work upfront to figure out how fast the boat could move.We had to figure out, what’s the maximum speed it can move, with the river moving at X speed? How much more does that give us on our boat speed? Because one negates other.

b&a: How did you build the river environment?

Luke Millar: The whole thing was one large land simulation, where literally, the water started off at one end, and it ended up going over the waterfall at the other end. It wasn’t chunked up into pieces, but we did add layers of detail as you went closer to the surface. So the ground at the bottom of the river was quite chunky. And then as you got further up, one core sim fed into the next more detailed sim, and that fed into the next more detailed sim.

On top of that, we’d developed a way of being able to blend any other detailed sections in. So if the boat needed to then spin around or go backwards or do anything like that, we could actually do a subtle self-contained sim that would take the main river as an input, but then you could blend it back into the rest of the big river.

It really pushed our computing power here at Weta. To do the whole river was about a two-week turnaround. Every time we got notes from the client, our FX supervisor would always wince just a little, especially if it was like, ‘It’s great, but I don’t like this rock here…’.

Fortunately, because we had set our boundaries and our rules up, it meant that everything did feel very real. And we weren’t having to combat the usual things of splashes that went three miles into the air, because the boat was going at 200 kilometres an hour, all of those kind of things that usually trip you up. From that point of view, it actually went quite smoothly, to the point where they kept on adding more shots, because it got more and more exciting.

b&a: What tools does Weta now use for that kind of water simulation?

Luke Millar: For this show, we used a combination of Houdini plus some proprietary tools to read in the caches and blend it together. It was great, because it did allow us a good flexibility, which was nice. It gave us a lot of control, and obviously artists were very familiar with it. So it made the process quite straightforward.

b&a: How did you tackle the bubbles, in particular?

Luke Millar: They did do a plate shoot in a river in Colorado. The river there is about three times wider than the rapids, but it gave us some good visual references. There’s as much bubbles under the water as there is above the water. We had to do a lot of bubble simulation, not just what was sitting on top, but what was actually underneath, to make sure that when you see between the foam that it still looked like turbulent, aerated water.

b&a: How were the actors filmed for this sequence?

Luke Millar: They built a huge tank of water, and the boat was always on water. I don’t think it actually floated, but it was on at least an articulated arm underneath water. And then they fired a lot of water jets, blowing air into that tank to start to try and simulate the turbulent rapids. Then they had wind machines which gave us a lot of in-camera spray.

Now, when we actually tried to transplant and blend that water back into the digital water, it became quite tricky. So there’s a few shots where we are using the practical water in the movie, which is great to see. But as soon as you started to get a little bit of distance from the boat, it became easier to take the CG water right up to the hull.

For some shots, too, they couldn’t move the boat, the practical boat, fast enough. So we obviously had to hijack that a little bit and add additional movement to both the plate boat and the camera to have it travel through the environment at a faster rate.

b&a: One thing I also loved in that sequence was the wider environment in those shots. How did you leverage some of Weta Digital’s tools to produce foliage and jungle imagery?

Luke Millar: As part of the production, we went on a plate shoot to the Amazon, which was amazing. It gave us absolute real world reference. We would take sections of real world Amazon jungle, and then built up from there. It was like pre-canned dressed building blocks with foliage, with pre-canned motion, for birds and monkeys and all sorts of things, butterflies even.

Then we’d start to construct the wider jungle from laying out all of those building blocks together. We could also do an additional dressing pass, just to vary them up from scene to scene, so it felt that we were travelling to different places. It was a bit of a different approach. Normally, we’d build the whole environment and then populate out trees along the whole space. But once you got off the banks of the river, it was very dense foliage, so it didn’t make as much sense to do that. We wanted to get that real world fidelity along those river banks, with the plants that are in the water.

One thing we did do, though, especially in those wides, is you could start to see a lot of repetition, which is not actually dissimilar to what you do see in the real Amazon. You do see a lot of repetition, because the jungle is so dense. To deal with that, we added some additional vines layering up over the top, to start breaking up areas and also bridge tree to tree growth, which is the thing which you typically don’t get when you start placing plants. You build a tree, and you start placing it amongst your environment. You don’t get a lot of interconnected foliage between the pieces. That was a nice way of bringing all the components together.

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