Pixar’s Inside Out 2 is a journey into anxiety and the changes in our belief system. Although this concept is metaphorical in our lives, it’s very much a real place in Riley’s mind and one that had to be meticulously crafted by the brilliant artists at Pixar.

Strings

Early concepts by Pixar’s Art department envisioned a place inspired by nature with a focus on harmony and elegance, an aesthetic which was very closely followed by the Sets and Effects departments.

To make sure the look was art directable, the Effects team created rigs of strings for the belief system, which were later passed down to Presto, Pixar’s proprietary animation system, via Houdini Engine and openUSD.

The shading of the strings was another important challenge, as it needed to convey a sense of energy slowly rising up towards Headquarters. This was achieved by layering together several animated shading signals, with separate controls for the timing and frequency of each component. “Wide shots typically called for larger-scale, faster-moving patterns compared to tighter shots, to create a sense of scale while not being distracting,” said Brandon Montell, Lead Sets TD at Pixar. The different shading signals were fed into Arbitrary Output Variables (AOVs) so that compositing artists could have control over their strength in the final image.

This shading rig was built in Flow, Pixar’s proprietary shading tool, giving artists control over the glow colors, helix twist, animation speed, and more. “We wanted the strings’ material to have an ethereal, volumetric effect,” Brandon added. “We found that we were able to achieve the majority of this by animating the opacity and glow on the surface of the string meshes, instead of rendering any volumes or animating the geometry. By fading out the surface presence at the edges and breaking it up with noise and helical ribbon shapes, it created the illusion of an internal structure. This was huge for being able to iterate on shaping and timing, because the effect was lightning fast to render.”

The Sets and Effects team also worked together to generate particles at render time with Houdini Engine, to finish off the shimmering subtleties in the strings.

Water

The water was a different challenge, where the memory orbs needed to interact with the water and create a whimsy. “We knew that there would be these grand strings and pools of water, but we knew there were many opportunities to do something different and abstract with the water effects,” said Alyssa Lee, FX artist at Pixar.

“The only simulation involved is a really fast 2D particle simulation, with particles that float around from a noise force and repel from any input objects. After that was simulated, we randomly stretched out the Z position of each particle, increasing the scale and softness as they got deeper. This helped fill in large areas while still seeing detail on top. In the end they got rendered as planes with a soft circle texture,” continued Alyssa.

In the end, particles were sourced from the edges of the terrain, strings, and memory spheres and later rendered with RenderMan on a separate layer and composited in Nuke. “We also wanted to be able to represent flowing water, so we made a similar particle system, but with a sideways force,” added Alyssa.

To rough out the position of the waterfalls, the FX team created a Houdini Engine asset, which allowed the Sets team to dress the waterfalls. “Instead of rendering them as circles, the flowing version takes the trail of each particle and uses that to create a ribbon. Then the ribbons were rendered with the same soft circle texture,” Alyssa concluded.

Lighting

The initial concept was to have the strings predominantly made up of large beads of energy traveling upwards, with large glowing orbs forming a significant aesthetic of the strings.

Inside Out 2 © Disney/Pixar

Art by Noah Klocek and Jason Deamer

“Some of our early lighting tests leaned into the idea of the large orbs. This led to the beads being the brightest source of light, plus we used fog and glow in comp to really make them pop,” said Eman Abdul-Razzak, Lighting TD at Pixar.

“During production, we decided to move away from the large orb idea to avoid having two spherical visual elements compete for attention in the frame. Instead, we used the beads as a way to illuminate the strings. This allowed us to ‘feel’ the beads instead of seeing them. We started to hone in on the idea of the strings being the main focus of the belief system,” added Eman.

Another thing the lighting team tested early on was the illumination from the strings onto the set, which was achieved with Foundry’s Katana, and relied heavily on RenderMan geometric area lights or mesh lights, for subtle water interaction. “Initially I had tested just using all the string geometry as a mesh light, which quickly proved to be way too expensive for render times, and it also acted more like a general fill light, which wasn’t the intended look,” added Eman. “To improve this, Allysa created an optimized string geometry cut off just above the waterline, which significantly reduced render times and provided a more localized lighting interaction between the strings and terrain,” continued Eman Abdul-Razzak.

“In special cases where characters were directly interacting with a string we would just create an additional mesh light for that shot using a single string, which helped us optimize render times and have more artistic control on that localized light,” said Eman.

Compositing

After using RenderMan’s machine learning denoiser to clean up noise typical in pathtracing, the lighting team also uses Nuke extensively to compose our beautiful renders. Although we strive to get as close as possible to the final output in the renderer, typically, volumes are rendered separately and many Light Path Expressions (LPEs) and Arbitrary Output Variables (AOVs) accompany the final renders, also called beauty passes, to have finer control in post.

“With multiple visual elements such as the memory spheres, water FX, terrain, and of course the strings, Nuke was really a beneficial tool for being able to dial in each of the elements in a quick and iterative way,” said Eman Abdul-Razzak, Lighting TD at Pixar. “There were also specific elements created in Nuke, like the string auroras and lensing effects which did well to tie the image together and really enhanced the ethereal feeling of the belief system,” she concluded.