‘This is where we add the 30 foot liquid metal shark’

#Shotmakers: Weta Digital breaks down this fun single scene from Robert Rodriquez’s ‘We Can Be Heroes’.

Today I’m launching a new series at befores & afters called #shotmakers. It’s about looking at a single shot or sequence with the VFX team from a particular project and breaking just that shot or sequence down.

The first article in this series is a super-fun one about Weta Digital’s work on a scene from Robert Rodriquez’s We Can Be Heroes. The sequence features superhero kid Guppy (who happens to be the daughter of Shark Boy and Lava Girl) conjuring up a liquid shark, and then riding it, before it eats some Squiggle Monsters.

Here, Weta Digital visual effects supervisor Dan Macarin and sequence visual effects supervisor Mark Gee break down how the studio made the shark scene happen.

Background to the scene

Dan Macarin (visual effects supervisor): We have worked with Robert Rodriguez several times in the past and when he approached us on this project he wanted the designs to be simple, as if kids designed them. He also wanted the saturation levels to be punched up, and the humor to always be a part of the storytelling.

When working with Robert, it’s always a wild ride. You ask him what he wants to do next and you hear something like, ‘Well, this is where we add the 30 ft liquid metal shark’. Needless to say it was a lot of fun to work on this film.

Early on in the classroom scene Guppy shows her ability to manipulate water. She jokingly creates a water shark that mimics the poster for the movie Jaws. Not long after this you see Guppy’s father riding a great white shark before he heads into battle. So the shark itself isn’t a random idea in the movie, it’s an ongoing part of the story. It’s a sort of back and forth between Guppy and her parents, each going bigger and bigger with their powers.

Vivien Lyra Blair as Guppy on the greenscreen set.

The creative brief

Mark Gee (visual effects sequence supervisor): As the daughter of Shark Boy and Lava Girl, Guppy has the power to manipulate liquid. During the battle against the Squiggle Monsters, Guppy creates various liquid weapons but quickly gets into trouble when she runs out of water.

As a last-ditch effort, Guppy channels the liquid metal pyramid and creates a giant liquid metal shark. She jumps on its back and commands the shark to attack and defeat two of the Squiggle Monsters with a few big bites.

Robert Rodriguez wanted the shark to materialize over four shots. At first, you can’t decipher what Guppy is creating; you only see her summoning a stream of molten metal out of the pyramid. This begins to pool together, forming a basic shark shape. Guppy turns away from the pyramid and whips the form into a fully formed giant liquid metal shark ‘swimming’ through the environment.

Animation pass.

Shooting the scene

Robert had produced some rough assemblies in editorial for the shark shots, but he also wanted flexibility in post. Live-action was shot on a greenscreen stage with a partial floor build and the console that Wheels operates. We removed the practical floor in the first shot and replaced it with our CG environment, giving us more control over the CG lighting and assets.

The ‘swimming’ shark shots were the most challenging. We shot everything we could in-camera, then Robert worked with Weta’s animation supervisor Stephen Clee and his team to design the final shot. Guppy was shot riding on a shark gimbal against greenscreen, and a Technocrane was used for the camera move. Our animation team put Guppy on a card rig to give Robert the flexibility to pull back on the virtual camera just before the shark bites down on the Squiggle Monsters.

We used the same method for the shot where Guppy and the shark are chasing down the Squiggle Monsters. The original plate was shot wider than what you see in the final shot, but the shot looked far less dramatic that way. Animation pushed the camera closer to Guppy and the shark for more of a POV feel, which helped create more drama in the shot.

The scene takes shape with the CG shark.

Making a liquid shark

Guppy forms the shark with liquid-metal from the pyramid, but Robert didn’t want its surface to look exactly like the pyramid’s—more of a derivation. The shark needed to look menacing but not so scary that it would give the kids nightmares!

Robert had a scale model of the shark’s head from Jaws which we used as reference for the head and mouth area. For the body, we referenced a great white. Once we had the basic model, we experimented with shading. We started by with an adapted version of the pyramid shader, but these first tests were too chrome-like and grey. Robert wanted more complexity to the texture and color to correlate with the surrounding environment.

We experimented with various levels of specular roughness and reflectance before settling on a multi-layered approach and outputting various AOVs to give comp full control over the look and keep it consistent across various lighting.

The FX department also got involved by simulating a ripple-like liquid flow over the shark’s surface, which was very similar to what they had done with the pyramid. Even though this is subtle, it added to the complexity of the surface

FX also created the liquid metal trails left in the sharks wake, and FX artist John Perrigo came up with the idea of having liquid metal ripples around the shark fin when it first lands on the pyramid platform. This was a really nice solution to the tail penetrating the floor in those few shots.

Guppy composited in.

Animating a liquid shark

Robert wanted a large menacing shark. He didn’t want it too cute or cartoony looking or to look as though it was smiling. It was to be more of a Jaws moment on a kids level. But when we first showed Robert the initial animation, he thought the shark looked like it was smiling! So we had to go back and adjust the mouth shapes to give us a more serious-looking shark.

To sell the scale and mass of the shark, we kept the motion slow and flowing. Even when the shark bites down on the Squiggle Monsters at the end, the jaw comes down slowly but with force. At that point, we deformed the jaw around the walkway as it hits and added camera shake to really sell the point that this is a huge shark with a lot of punch behind it.

As bad-ass as the Squiggle Monsters are, we added some light-heartedness and humor to the sequence by seeing them try to escape as Guppy and the shark chase them down. The Squiggle Monsters then get cornered and huddle together shaking in fear as they realize they’re about to be chomped. Finally, as the shark bites down on them, their tentacles are left out wriggling like they are still trying to get away. Hopefully that was enough to get a laugh out of the kids rather than a scream of horror!

The final shot.

Delivering a virtual set

We spent a fair amount of development time on the virtual set, especially with the look-development of the pyramid. Since there were so many shots that featured this environment, we also worked out the most efficient ways to render and composite the shots together.

Lighting-wise we built one large lighting rig which worked for a majority of the angles. There were only a handful of shots that we had to beauty light, but in a lot of cases, we rendered out multiple shots from one Katana scene. Since we were dealing with a very reflective environment that was angle-dependent, lighting outputted various AOVs to help comp balance the shots together.

The look of the pyramid was very angle-dependent, and there was a lot of iterating before we had something that worked, and Robert liked. In the end, lead compositor Michele Benigna took over the look development of the pyramid after basic render passes were done and created a 3D set up in Nuke that the compositors could use and place in their shots.

This was also the case for the spinning vortex below the walkways. It was entirely a comp solution using textured spheres and glows and an Eddy simulation to add to the atmospherics of the vortex.

Once all of this was set up, we created templates in comp for the various scenes, and were able to quickly turn the virtual sets for the shots. The challenging part was when we had to integrate any of this in with the live-action, especially when we had to match the pattern and alignment of the CG walkways to the onset walkways, as they were rarely the same orientation. In many cases the fastest and cleanest way around it was to roto the actors off the plate and replace the walkways.

The biggest comp challenge in the shark riding shots was integrating Guppy onto the shark. Because of the way Guppy was shot with the green screen covering some of her legs and hands, we had to push her down a little more than we had hoped. Making it look convincing that’s she’s sitting there riding on a giant reflective liquid metal shark isn’t easy, but the compositors did a great job with that.

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