Post on 17-Dec-2015
Cell-Projection of Convex Polyhedra Volume Graphics ‘03 Stefan Roettger, University of Erlangen Tokyo
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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
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• 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
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• 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
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• 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
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• 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
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Example Images
Bluntfin8 fps
Campfire50 fps
Neghip22 fps
Cell-Projection of Convex Polyhedra Volume Graphics ‘03 Stefan Roettger, University of Erlangen Tokyo
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• 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
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Emission vs. MIP
25 fps 50 fps