Computer Graphics World

March 2009 18 n n n n CG I•Stereoscopy Dick Walsh, who received a Scientific and Technical Academy Award in 2002 for developing PDI's facial animation system, rigged BOB's face. "I was proud that we re ally challenged Dick [Walsh] to fulfill a lot of unusual requests for our movie," Burgess says. "When you can tell him to give me a guy with one eye, a huge mouth, multiple chins, brow ripples that come and go, and to swivel the eye around the head, then he gets excited." In his blobby state, BOB was a consis tent set of metaballs. "Imagine 30 flat meta balls that could separate running up and down a spine," says Boylan. "His head can separate between his mouth and his eye, or under his mouth." To create arms and fin gers, the crew added curve primitives to the studio's metaball system, which previously used ellipsoid primitives. en, to bring the two versions together, the character TDs developed a system that mapped from the metaball version to the patch version, and used the patch version, that is, the motion system side, to warp the metaball version. In other words, it was like wrapping a lump of JellO with a net, and then pulling on the net to squash the JellO into specific shapes. "It all comes back to having two differ ent representations and blending between them," Boylan points out. We blend be tween one patch and one tessellated surface; the patch drives the tessellated isosurface." In practice, BOB is always both versions at the same time—both versions plus one. A second patch version made it possible for BOB to lose his head and rotate his eye. "In order to make that gag work, we needed two different patch versions that work in concert," Boylan explains. One goes with the head; one stays behind. Similarly, a surface patch version of the eyeball model can orbit BOB's head. e system blends between the patch surfaces for the eyeball and the head. e animators saw a simple version of BOB with rigid polygons parented to joints, but they could dial in more details as they wished. "One of the true challenges from the production side was how to make a character with an implicit surface inter active enough for animators," Boylan says. "It took a lot of special optimization code written in C++ and a lot of work from R&D, as well, to get that performance. But, the animators could go all the way from a standin version in onetenth of a second to a final version that took two or three minutes." For BOB's face, animators could work with a surface representation, but as soon as the character needed to be blobby, they switched the view. Special deformers rep resented BOB's contact with the ground, but when BOB touched something, ani mators needed to work with the higher resolution versions. In addition, because bubbles inside the blob added to BOB's performance, animators could use the rig to control a bubble simulation. "One challenge was making sure all his gags played well together," Boylan says. At one point, I was describing how BOB worked to our lighting supervisor, and he said, 'You know, you guys could have said no.' But, we didn't want to say no." Blob Lighting As it turned out, creating a patch version of BOB provided advantages beyond anima tion. "One of the things that characterizes BOB from a CG standpoint is that we have a polygonal mesh made of triangles that can change in every frame, and there's no consistency from frame to frame," Boylan says. "at becomes a problem for light ing. So, for purposes of lighting, we had a map ping that occurred between the im plicit surface and the reference BOB has popped his arms out of his amorphous body to make a point, thanks to a sophisticated rigging system that gave animators control over his blobby form. Behind him, The Missing Link and Dr. Cockroach used more traditional bipedal rigs.

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