Cell-Projectionof Convex Polyhedra

Stefan RoettgerThomas Ertl

University of Erlangen

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

Cell-Projection of Convex Polyhedra Volume Graphics ‘03 Stefan Roettger, University of Erlangen Tokyo

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Thanks for your attention!

Fin