Paws, claws and jaws in Attack the Block

In director Joe Cornish’s debut feature film, Attack the Block, a South London teenage gang squares up against an army of invading alien monsters. Stockholm visual effects and animation studio Fido contributed around 100 shots to enhance the on-set creatures. We take a look at how they created CG fur, paws, claws and jaws for the film. Warning: spoilers.

Enhancing monster movement

On set, stunt performers were filmed in practical creature suits with animatronic jaws designed and created by Spectral Motion as dark and menacing aliens. “One of the main points about the creatures was that they have a negative light – they’re always the darkest thing in the picture,” says Fido’s senior visual effects supervisor, Mattias Lindahl. “The characters even say, ‘I’ve never seen anything so dark before in my life’. I think Joe always thought there was going to be some grading work to enhance the suits where it was needed and initially the idea was going to be to grade these creatures down and take off the highlights.”

Ultimately, Fido was called upon by principal vendor Double Negative to carry out a number of effects enhancements for the creatures in terms of their fur, jaws and front legs. Lindahl, it turns out, was actually involved in some of the early production meetings for the film while still working at Dneg in London, and then revisited the film back in Stockholm.

“The suits had quite long front legs,” says Lindahl. “The stuntmen did such an incredible job running around on stilts, but they couldn’t really get the front joint working for the paws, so we ended up creating CG paws and claws. The suits were always great reference for our work.” Fido artists tracked the paws, adding secondary animation in Maya to allow the paws to turn and have deformation. In addition, artists would paint in various gaps or remove hints of human-like motion in the limbs.


The jaw rig

Fido worked also on enhancing the animatronic jaws, seen on screen as luminous sets of teeth, and in some scenes when the creatures’ mouths were closed, almost as peering eyes. “The animatronic jaws looked great on film,” notes Lindahl, “but in terms of the expressions, Joe wanted to show them sniffing, growling, grinning and making a big roar. So we ended up mostly replacing the jaws in CG.”

Beginning with photographs of the animatronic jaws and new concept art, Fido fleshed out the look of a new CG muzzle, complete with extra teeth inside the throat. “We created a series of key frames that could be stepped through to illustrate movement and poses,” says Lindahl. “Then once Joe was happy with the design and the key poses, we started the work on the modeling and rigging.”

For that, Fido’s Magnus Eriksson took the key frames into ZBrush for sculpting and then used Maya to create the animation rig, which was shaded and rendered by Aron Makkai in RenderMan. “While working on the design and placement of all the teeth we used transpose throughout the process to make sure that the design was functional and could accommodate the movements of the jaw,” says Eriksson.

Grey shaded render of inside the jaw

“Once the design was finalized, an animation mesh was created based on the digital maquette and all the details were transferred from the maquette to the animation mesh. After a final cleanup and detailing pass the mouth ended at 24,000,000 polygons and each tooth at roughly 2,500,000 polygons. We then brought these high resolution models into Mudbox to generate the displacement maps.”

“When building the rig for the mouth,” adds Eriksson, “we needed a great deal of control in how to animate the jaws since we needed to match the head movements of the filmed monsters but still create animation that went beyond what they could do and still feel believable. This included individual controls of the upper and lower jaw, tools for the animator to control the rotational pivot of the mouth and a combination of blend shapes and direct controls for the lips and throat. To achieve nice deformations on a mouth that should be able to open 180 degrees we decided to use Comet’s Pose Base Deformer tool.”

Furthering fur

A two-pronged approach was taken for the fur. Where there was a significant amount of parallax involved as a creature was turning around or the camera was moving, Fido relied on a CG fur solution. For shots with less movement, patches of fur were tracked onto the creatures. “Joe wanted to push the look of the fur a bit further to make it spikier, clumpier, more hard shaped and contrasty,” notes Lindahl. “A lot of work went in to transforming the actual look of the fur, but also in changing the shape of the creatures to make sure there were no clues left to the fact that these alien creatures were actually stunt performers in suits.”

The CG solution began with a complicated body tracking process of the live-action performers using a rough model of the creature. “We made a rig that allowed us to both animate or roto-mate the creature to the plate, but also push the geometry around to fill in the areas that were needed in screenspace,” says Lindahl. “A lot of time was spent on roto-mating the creatures. It was of course important that the mesh matched the plate on every frame, but we also had to make sure that the animation was smooth enough to not end up with any twitchy sudden moves that would then translate to how the fur behaved.”

To create and render the fur, Fido started with the built-in system in Houdini and Mantra and then worked on extra details such as clumping and dynamics. “We then wrapped it up into a neat little package,” explains Fido’s Timmy Lundin, “which made it easy to import any number of animated monsters from Maya, apply the fur and have easy access to commonly used parameters such as clumping density and profile, hair length, hair density and so on for each of the four different fur systems each monster consisted of. When required we could easily paint specific attributes onto our skin mesh to control the look of the fur.”

The 2D approach, for shots where little parallax was occurring, were completed in Nuke using patches of pre-rendered fur. Says Lindahl: “Sequences of fur moving were rendered out with an alpha and used by the compositor by tracking the motion of the creature and applying a new updated outline to the monsters. It worked great for shots where you only really saw the creature from one angle.”

Fido developed a ‘startup script’ in Nuke with a given structure so that the 2D fur shots could be done in a similar manner. “All shots were de-grained with the Neatvideo plugin for Nuke,” says lead compositor Fredrik Höglin. “Then, at the end of all scripts we made a hard dif key, applied scanned grain and then slapped all the modified re-grained pixels onto the original grained plate, to make sure we would not be modifying pixels we shouldn’t and at the same time applying correct grain to every modified pixel.”

“We used Mocha to track the background to create clean plates,” continues Höglin. “In most cases we couldn’t use Mocha or the tracker in Nuke to track the motion of the monsters due to the fact that the fur was always moving, so plain old hand-tracking had to be done. Joe encouraged us to experiment with the motion and shape of the monsters. We strived to get away from the light floppy puppet feeling, and make it more heavy and aggressive.”

Breaking down the grand finale

Fido’s visual effects work is seen most notably in the film’s final showdown between the teenagers and the creatures in the apartment block. Here, one of the lead characters, Moses, is chased down a corridor by 15 creatures before a set of fireworks is let off against the beasts.

“For that sequence,” explains Lindahl, “they shot the actor running down the corridor on a replica set with two guys in suits after him. Repeat passes were then shot of the additional creatures on greenscreen, without the help of motion-control. Careful tracking and stabilizing of each individual creature had to be applied to make them sit in with the main plate. Each individual creature was body tracked to allow us to replace the fur and jaws. We also added CG claws and front paws to each creature, both to help making the creatures scarier looking, but also to add a wrist to the front leg to smooth out the motion of the run.”

To realize the fireworks shots, production again filmed passes of the monsters running through the frame knocking over furniture and with interactive lighting. “They shot fireworks elements but unfortunately we weren’t able to extract them,” says Lindahl. “However, the director loved the reference footage, so we had to re-create it in CG and exactly match what the director liked. We had a Houdini solution for the smoke trails, using 2D fluids and exporting a lot of positional data to Nuke in terms of locators to make sure the compositors had full control of things like the flares for the fireworks.”

For Lindahl, Fido’s 100 Attack the Block creature shots, completed over a four month period with a team numbering around 25 artists, lent a distinctive feel to the film. “It’s actually one of those things,” says Lindahl, “looking back at it, if you would have done it differently by going in with a completely CG creature, it would have been a completely different look. What we created in the end was something quite unique. I think the audience isn’t quite sure what they’re looking at. Is it real? Is it CG? It’s not easy to tell.”

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