Transcript Cell-Projection of Convex Polyhedra

Cell-Projection
of Convex Polyhedra
Stefan Roettger
Thomas Ertl
University of Erlangen
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
Stefan Roettger, University of Erlangen
Volume Graphics ‘03
Tokyo
3
Emissive Optical Model
• Use emissive optical model (Max ‘95)
• Does not require sorting
• Ray integral = length of ray segment times average
emission (assuming linear interpolation)
Cell-Projection of Convex Polyhedra
Stefan Roettger, University of Erlangen
Volume Graphics ‘03
Tokyo
4
Projection of Convex Polyhedra
• The graphics hardware can take over the projection of
arbitrary convex polyhedra
• Based on bounded layered fog (Mech JGT ‘01)
Cell-Projection of Convex Polyhedra
Stefan Roettger, University of Erlangen
Volume Graphics ‘03
Tokyo
5
PCP Algorithm
• 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
Cell-Projection of Convex Polyhedra
Stefan Roettger, University of Erlangen
Volume Graphics ‘03
Tokyo
6
Performance
• 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
Cell-Projection of Convex Polyhedra
Stefan Roettger, University of Erlangen
Volume Graphics ‘03
Tokyo
7
Example Images
Bluntfin
8 fps
Campfire
50 fps
Neghip
22 fps
Cell-Projection of Convex Polyhedra
Stefan Roettger, University of Erlangen
Volume Graphics ‘03
Tokyo
8
Ground Fog
• Triangulated terrain
• Place prism on every base triangle
• Assume constant emission in each prism
Cell-Projection of Convex Polyhedra
Stefan Roettger, University of Erlangen
Volume Graphics ‘03
Tokyo
9
Emission vs. MIP
25 fps
Cell-Projection of Convex Polyhedra
Stefan Roettger, University of Erlangen
50 fps
Volume Graphics ‘03
Tokyo
10
Fin
Thanks for your attention!
Cell-Projection of Convex Polyhedra
Stefan Roettger, University of Erlangen
Volume Graphics ‘03
Tokyo