Interactive Rendering of Translucent Deformable Objects Tom Mertens 1, Jan Kautz 2, Philippe Bekaert 1, Hans-Peter Seidel 2, Frank Van Reeth 1 1 2

Overview Goal Previous work Translucency model Our method Implementation Discussion, results and future work

Problem: Translucency BRDFBSSRDF

Previous work Jensen et al. (SIGGRAPH ’01): –BSSRDF model Jensen et al. (SIGGRAPH ’02): –fast, production quality rendering Lensch et al. (PG ’02), Hao et al. (GI ’03), Carr et al. (GHW’03), Sloan et al. (SIGGRAPH’02-’03): –interactive, real-time rendering with precomputation Our paper: –interactive rendering –varying geometry and material (no precomputation)

BSSRDF model function of distance introduced by Jensen et al. (SIGGRAPH’01) multiple scattering materials with high albedo: marble, milk, wax, skin,…

BSSRDF model function of distance introduced by Jensen et al. (SIGGRAPH’01) multiple scattering materials with high albedo: marble, milk, wax, skin,…

Integrating the BSSRDF hierarchical approach (Jensen et al. ‘02) –decouple light and surface sampling, –decouple light sampling from geometry –2-pass method: irradiance sampling – integration with octree –limitation: rebuilding samples & octree our method –integration ~ hierarchical radiosity mesh based: beneficial for geometry updates hierarchy = clustered triangles form factor for BSSRDF: fast local integration

Our Method boundary element method

Our Method boundary element method discretized irradiance discretized radiance

Our Method boundary element method form factor discretized irradiance discretized radiance

example

sample irradiance

pull irradiance

link roots

subdivide link

subdivide link again

gather

push

Hierarchical Evaluation hierarchy = clustered triangles –tree hierarchy subdivision: 4-to-1 splits face clustering evaluation ~ hierarchical radiosity 1.irradiance sampling + pull 2.construct link hierarchy 3.gather over each link 4.push + average at vertices “oracle” = solid angle interactions at different levels –speed advantage

Form Factor: (mid)point to triangle semi-analytical –Taylor expansion advantages: –fast –accurate –noiseless indispensable for local integration more distant: 1 sample area integral integral over edges recursive midpoint

Form Factor: point to triangle semi-analytical –Taylor expansion advantages: –fast –accurate –noiseless indispensable for local integration more distant: 1 sample

Form Factor: point to triangle semi-analytical –Taylor expansion advantages: –fast –accurate –noiseless indispensable for local integration more distant: 1 sample point samplingform factor

Implementation stored links –incremental updates –promote/demote links –real-time frame rate render on-the-fly –instant feedback –less memory overhead –interactive frame rate irradiance –point light (+ shadow) –environment map GPU –fresnel –tone mapping –shadow map

Results 5-10 fps for 10-20K tris models –dual Xeon 2.4Ghz; ATI Radeon 9700 Demo video material changecandle twistshadow leakPerlin noise deformation

Discussion practical technique for interactive applications speed advantage over previous hierarchical algorithm: –gathering in higher levels –efficient local integration –consistent hierarchy after deformation limitation = mesh –needs hierarchy –limited by resolution –fixed topology interactive applications often mesh-based anyway

Future Work recycle radiosity techniques –adaptive meshing, high order interpolation,… –improved oracle function varying topology full GPU implementation non-homogeneous media

Acknowledgements Jens Vorsatz (mesh hierarchies) P. Debevec (light probes) funding: –European Regional Development Fund –Marie Curie doctoral fellowship