CGSociety

A far and near based setup simplified the artist's job of determining and correcting the stereoscopic shift. Trying to calculate without those controls meant every time a lens was changed, the distance of the lens to the nearest object would require the calculation of a new interaxial distance. “You might have a number which is 1.0582, and you want to give it 5% more stereo volume, but the numbers are so complicated that it’s hard to get a language of what you want and how to get it. When we use the tools we have now, we are talking a simple language of pixel shifts. I’ll give notes like ‘near plane should be set on Dr. Cockroach at negative 20 pixels and make the back of the room at plus 10’. If we decide to make the room look deeper, I can say ‘OK, let’s make the background plus 15’.” It’s a surprisingly sensitive process. “If we put in a sky element and it looks a little two close to some buildings, we’ve done as little as shift that background by half a pixel in one of the eyes and be able to drop that back in space just enough so it feels more natural.”

The B.O.B. Blob
Five different departments worked on the animation and look of B.O.B.. He was created and rendered entirely in proprietary software, using a new technology. The first decision was whether or not B.O.B. should be created through FX or as a character. In the earlier versions he was much more blob-like, more of a traditionally rendered isosurface, but within a few months it became clear that he couldn’t look like an effect in a world populated by the usual characters. Normally that would mean the design would be entirely an FX task instead of animation, but B.O.B. had to be treated as a main character and not as an effect, while still having character FX handling much of his technology.

The result was B.O.B.s animation controls looked more like a Slinky toy, a cylindrical shape that could be posed. “One thing that was tricky,” said Boylan “was making sure all the built in gags played well with each other. There were definitely some constraints, but we didn’t want to restrict the animators too much.” A simplified rig was given to animation with controls that were reasonably familiar, basically a tube with arms that could turn on and off. One plate was included that could be placed at the proper tearing point separation was needed for scenes where B.O.B. tries to pass through something and breaks in two, connecting again in a later scene. Any more pieces had to be done in Character FX.

Character FX
Various gags included B.O.B.’s interaction with the environment. A special deformer called the ground deformer, written by Scott Cegielski in FX, showed the contact between B.O.B. and when he’s sitting on the ground. Different parts of his face, which at times occupied two-thirds of his body, could blend on and off, disappearing into the blob surface then reemerging. His head could detach, his eye could float and move separately from other parts of his face, and could come out of his body. “He was transparent,” Boylan added, “which means that all of his internal anatomy had to be visible. He had a mouth interior that needed to be visible without drawing unnecessary attention, and it had to deform properly. This affected the character rigging because traditionally, characters are built with layers of skin, starting with the skeleton to muscle structure to the surface. All of B.O.B.’s deformations had to be completely volumetric. That was something we didn’t realize until we started to have problems with the interior of his mouth poking through the back of his head, etc. We had to fall back and rethink our approach on deforming him.”

One of the big gags throughout the film was B.O.B.’s arms turning on and off, appearing from his body. B.O.B.’s arms appeared when he needed to gesture then they disappear back into the surface of his body. The rigging allowed for the arms to be detached from the body if needed. “Another thing that was very helpful was per vertex attributes which allowed us to embed a lot of information into B.O.B.’s model. If you were to look at B.O.B.’s polygonal model, there is a vertex attribute called “arm weight” that determines how much of that vertex is his arm. Parts on his torso would have a ‘0’ value, and parts on his arm would have a ‘1’, and vertices midway would have a value in-between. I was able to do that as part of the rig, then that information, the surface texture and surface ID information was picked up later on by Lighting for doing motion blur or other things. That was crucial. There were two things that were tricky with B.O.B. that made him different. One was generating proper surface normals and the other was generating motion blur.”

Interior bubbles gave B.O.B. depth and volume inside. “He’s made up of a particle system of 12,000 volumetric bubbles that were part of the character rig, the most expedient place to put it, and it helped to deform the bubbles along with everything properly.” They added a simulation with a little spring motion in the bubbles based on dynamics in the characters setup as well. “If the motion was extreme enough to have the bubbles drift out of his body, they wouldn’t be counted and rendered. There was nothing for them to collide inside of him. It made sense with him. He’s not supposed to be made out of water and plastic bubbles inside; he’s supposed to be a viscous fluid where the bubbles are part of the volume.”

The meshes ended up being quite dense, hundreds of thousands of polygons, presenting yet another challenge, namely performance. Boylan ended up rewriting quite a bit of code in C++ to optimize performance. “Normally we work with a very C-like scripting language that is interpreted, but B.O.B. was a battle on two fronts; one was artistically achieving the desired effect, and the other was making sure his performance was sufficiently fast for our production.”

Two Sides to B.O.B.
It’s important that all the stereo is locked down before a scene goes to Lighting and Rendering, which was particularly challenging because B.O.B. was mostly reflective and refractive. Normally surfaces in a movie are predominantly diffused but in B.O.B.’s case it was tougher to define his shape. Rim lights normally used to separate something from the background were ineffective since the light wouldn’t land the way you expected it to. Digital Supervisor Mahesh Ramasubramanian described the solution, “In B.O.B.’s case, we needed so much control and fine tuning, we ended up putting him together more in compositing. He was broken down into multiple layers of reflections and refractions and rim lighting and normal passes.”