Interactive Ray Tracing of Skinned Animations

Johannes Günther, Heiko Friedrich, Hans-Peter Seidel, and Philipp Slusallek
The Visual Computer, 2006, (Proceedings of Pacific Graphics), pp. 785–792,
Taipei, Taiwan, 2006
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Recent high-performance ray tracing implementations have already achieved interactive performance on a single PC even for highly complex scenes. However, so far these approaches have been limited to mostly static scenes due to the high cost of updating the necessary spatial index structures after modifying scene geometry. In this paper, we present an approach that avoids these updates almost completely for the case of skinned models as typically used in computer games. We assume that the characters are built from meshes with an underlying skeleton structure, where the set of joint angles defines the character's pose and determines the skinning parameters. Based on a sampling of the possible pose space we build a static fuzzy kd-tree for each skeleton segment in a fast preprocessing step. These fuzzy kd-trees are then organized into a top-level kd-tree. Together with the skeleton's affine transformations this multi-level kd-tree allows fast and efficient scene traversal at runtime, while arbitrary combinations of animation sequences can be applied interactively to the joint angles. We achieve a real-time ray tracing performance of up to 15 frames per second at 1024 x 1024 resolution even on a single processor core.