Interactive Rendering of Translucent Deformable Objects

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Interactive Rendering of Translucent Deformable
Objects

• Tom Mertens1, Jan Kautz2, Philippe Bekaert1,
• Hans-Peter Seidel2, Frank Van Reeth1

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Overview

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

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Problem Translucency

• BRDF

BSSRDF
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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. (GHW03), Sloan et al. (SIGGRAPH02-03)
• interactive, real-time rendering with
  precomputation
• Our paper
• interactive rendering
• varying geometry and material (no precomputation)

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BSSRDF model

• introduced by Jensen et al. (SIGGRAPH01)
• multiple scattering
• materials with high albedo marble, milk, wax,
  skin,

function of distance
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BSSRDF model

• introduced by Jensen et al. (SIGGRAPH01)
• multiple scattering
• materials with high albedo marble, milk, wax,
  skin,

function of distance
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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

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Our Method

• boundary element method

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Our Method

• boundary element method

discretized radiance
discretized irradiance
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Our Method

• boundary element method

discretized radiance
form factor
discretized irradiance
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example
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sample irradiance
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pull irradiance
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link roots
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subdivide link
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subdivide link again
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gather
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push
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Hierarchical Evaluation

• hierarchy clustered triangles
• tree hierarchy
• subdivision 4-to-1 splits
• face clustering
• evaluation hierarchical radiosity
• irradiance sampling pull
• construct link hierarchy
• gather over each link
• push average at vertices
• oracle solid angle
• interactions at different levels
• speed advantage

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Form Factor
area integral

• (mid)point to triangle
• semi-analytical
• Taylor expansion
• advantages
• fast
• accurate
• noiseless
• indispensable for local integration
• more distant 1 sample

integral over edges
recursive midpoint
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Form Factor

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

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Form Factor

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

point sampling
form factor
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Implementation

• GPU
• fresnel
• tone mapping
• shadow map

• irradiance
• point light ( shadow)
• environment map

• stored links
• incremental updates
• promote/demote links
• real-time frame rate

• render on-the-fly
• instant feedback
• less memory overhead
• interactive frame rate

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Results

• 5-10 fps for 10-20K tris models
• dual Xeon 2.4Ghz ATI Radeon 9700
• Demo video

material change
candle twist
shadow leak
Perlin noise deformation
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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

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Future Work

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

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Acknowledgements

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