Interactive Ray Tracing of Skinned Animations

Abstract

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 × 1024 res­o­lu­tion even on a sin­gle pro­ces­sor core.