In developing a new approach to simulating muscles in creatures, we immediately ran into a familiar roadblock. Placing muscles by hand on each creature was too time consuming and expensive to be considered on all but the most hero creatures. We developed an approach that derived the positions needed for rigging and deformations from the geometry, as opposed to defining them by hand. This system, called BlockParty, has since been used extensively on "The Chronicles of Narnia: The Lion, The Witch and The Wardrobe" and "Pirates of the Caribbean 2: Dead Man's Chest".For "Narnia", there were numerous real-world creatures such as lions, bears, horses and boars, as well as mythical creatures like centaurs, fauns and satyrs. Because ILM came to the project late in the schedule, the creatures needed to be setup for motion capture, animation, crowd work and simulation on a very short deadline. With limited time and resources, rigging and setting up deformations for each model by hand was not an option. In addition, to allow for the fantasy creatures required, we were going to need a system that focused on flexibility, reusability and speed.Traditionally, rigging has consisted of placing each bone of the skeleton in the approximate location of the desired pivot of rotation. However, as the complexity of the rig grows, this quickly becomes impractical on a large scale. Figure 1: A human was used to create a gorilla, a horse was used to create a boar, and both were used to build a centaur. We created a system flexible enough to handle simple rigs quickly, while maintaining the scalability needed for complicated setups. Our approach was to create a template geometry mesh, called a "volume guide". Next, we created the rigs, deformations and muscles for human, horse and cat volume guides. We recorded the position of each rig element relative to the volume guide, and then sculpted the appropriate volume guide to match the high resolution creature geometry. By generating a field of transformations from the change in shape of the volume guide, we were able to accurately * derive the placement of joints, skin deformers, collision volumes, animation geometry, and muscle rigs, even with significant proportional changes (e.g. a horse being turned into a boar). The geometry based approach also enabled us to support asymmetrical creatures by storing a correspondence between vertices of the volume guide across a plane of symmetry. As a final step, the deformations driven by the rig were transferred spatially to the high resolution character. This process generated production ready rigs and deformations with minimal user input. In addition, we were able to adapt to client changes by simply updating the volume guide and then regenerating rigs and deformations in BlockParty.
Modular Creature ConstructionA second challenge on "Narnia" was to keep creature rigs consistent with a large setup team working concurrently. Given the short deadline, we needed the ability to quickly make changes across thirty creatures based on animator feedback. We b...
