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26 cgw j u ly • a u g u s t • s e p t e m b e r 2 0 2 1 3D with a Twist around the characters and environments. Another challenge was lighting the char- acters and determining how the brush- strokes would integrate with that lighting. "Similar to what we did on Spider-Verse, we broke the lighting. We quantized the normals, removed all the so shadings, and broke the shading down into bands of light. Then we broke that up into brush- strokes," explains Lasker. "Whereas on Spider-Verse, we broke it up with Ben-Day dots and hatch marks." Furthermore, the artists did not want it to look like the lighting was done by computers. "It looks like someone painted light around the body. We are imitating 2D cel anima- tion," says Art Director Toby Wilson. "It's ei- ther 100 percent lit or 25 percent lit; there's not a lot of in-between in order to make it look and feel like classic animation." The team additionally developed a paint- erly process for the trees, grass, and vegeta- tion, since it takes up so much of the frame. Once the vegetation was generated, the group developed a tool it had started using on Spider-Verse for Gwen Stacy's universe, to simplify geometric detail into swaths of color. "We could take a field of grass, and instead of it looking like every blade of grass was there, we would change it into patches of color," Lasker says. Meanwhile, the artists used Autodesk's Maya to build models in the human world with irregularities — they are lumpy, squishy, and wobbly — then developed a paint- erly depth-of-field style and inserted the brushstrokes into that. When the outlines were added on top, it accentuated that look even further. Also, the textures had a painterly, irregular style, which was married with the brushstroke detail. "It was tough. We had to figure out a formula for it," Lasker adds. For effects, the group used SideFX's Houdini. Lighting was done in Foundry's Katana (which originated at Imageworks), compositing was done with Foundry's Nuke, and rendering in Autodesk's Arnold. The Robot Realm The robot realm is introduced starting in the second act of the film. Whereas the Mitchells' world has a very specific visual feel and shape vocabulary, in contrast, the austere tech universe is full of sharp angles. It is more perfect and sterile, with clean lines and sleek, reflective surfaces. It is the exact opposite of the imperfect, hand- craed aesthetic that mimics 2D, since it is a world designed by AI. "Our look had to transition into [the robot world] over the course of the movie. What made it espe- cially difficult was that our characters had to exist in both worlds," says Lasker. For instance, the outline tools that produced irregular and messy results at the beginning of the film would have clean lines by the end. "We had this evolution happening slowly so the audience would just sense that it's happening but it wouldn't be that obvious," he continues. Generally, the robot world had a more typical CGI aesthetic but also required new shaders, tools, and workflows for the glitzy, flowy, reflective, ray traced look. Whereas the human world is smaller and filled with objects, the robot world is stark, open, and minimal. And here, everything is in its proper place. The backgrounds, meanwhile, project a feeling of isolation. All of this helps drive the performances. The main characters here are the unique Stealthbots, which had to move in a very clean way, despite how they break apart and reassemble into various geometric shapes. According to Lasker, when they first saw the designs of the Stealthbots, they knew that the bots needed to move in a unique way. Since they are made by an AI, which was made by humans, it would make sense there was some holdout of bipedalism, but that it was starting to evolve into some- thing different. So,, the group performed many tests, experimenting with different kinds of morphing, breaking apart, warping, and so forth, and ultimately landed on what is on the screen. To achieve this look, they developed two new tools. One is a tool that slices the robot like a knife, and one that uses Booleans to create positive and negative shapes inside the robot. The slice tool performs a macro of actions aer a simple click-and-drag of The Stealthbots break apart and reassemble into geometric shapes. For the film, Imageworks developed an outliner and brushstroke tool.