Cell-Projection of Convex Polyhedra Stefan Roettger Thomas Ertl University of Erlangen

Cell-Projection of Convex Polyhedra Volume Graphics ‘03 Stefan Roettger, University of Erlangen Tokyo 2 Introduction Unstructured volume rendering Cell-projection = PT algorithm of Shirley and Tuchman (’90) Main bottlenecks: sorting and tetrahedral decomposition (Wittenbrink ‘99) Current performance 600,000 tet/s (Guthe ‘02) Above 1,000,000 tet/s performance is completely memory bandwidth limited

Cell-Projection of Convex Polyhedra Volume Graphics ‘03 Stefan Roettger, University of Erlangen Tokyo 3 Use emissive optical model (Max ‘95) Does not require sorting Ray integral = length of ray segment times average emission (assuming linear interpolation) Emissive Optical Model

Cell-Projection of Convex Polyhedra Volume Graphics ‘03 Stefan Roettger, University of Erlangen Tokyo 4 The graphics hardware can take over the projection of arbitrary convex polyhedra Based on bounded layered fog (Mech JGT ‘01) Projection of Convex Polyhedra

Cell-Projection of Convex Polyhedra Volume Graphics ‘03 Stefan Roettger, University of Erlangen Tokyo 5 1st pass – enable A writing and front face culling – draw primitive with alpha=(d-min d)/  d 2nd pass – enable subtractive blending and back face culling – draw primitive again 3rd pass – disable A writing and culling – enable additive blending with alpha multiplied – draw primitive with rgb=emission/2 PCP Algorithm

Cell-Projection of Convex Polyhedra Volume Graphics ‘03 Stefan Roettger, University of Erlangen Tokyo 6 Emissive model: 212,000 hex/s on NVIDIA GeForce3 (Guthe ‘02: 120,000 hex/s) For maximum intensity projection one only needs to render each face once Performance is about 600,000 hex/s Performance drop is mainly due to additional passes Performance

Cell-Projection of Convex Polyhedra Volume Graphics ‘03 Stefan Roettger, University of Erlangen Tokyo 7 Example Images Bluntfin 8 fps Campfire 50 fps Neghip 22 fps

Cell-Projection of Convex Polyhedra Volume Graphics ‘03 Stefan Roettger, University of Erlangen Tokyo 8 Triangulated terrain Place prism on every base triangle Assume constant emission in each prism Ground Fog

Cell-Projection of Convex Polyhedra Volume Graphics ‘03 Stefan Roettger, University of Erlangen Tokyo 9 Emission vs. MIP 25 fps 50 fps

Cell-Projection of Convex Polyhedra Volume Graphics ‘03 Stefan Roettger, University of Erlangen Tokyo 10 Thanks for your attention! Fin