Project Week 25/Next Generation GPU Volume Rendering

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Key Investigators

• Simon Drouin (Montreal Neurological Institute, Canada)
• Steve Pieper (Isomics Inc., USA)
• Andras Lasso (Queen's University, Canada)
• Ole Vegard Solberg (SINTEF, Norway)
• Alvaro Sanchez (Kitware, USA Remote attendance
• Sankhesh Jhaveri (Kitware, USA Remote attendance

Project Description

Objective	Approach and Plan	Progress and Next Steps
Develop a specification for the next generation of GPU volume processing and rendering in VTK and Slicer The specification should support Multiple input volumes for ray-casting and slice-based volume rendering GPU-based volume slicing and compositing Programmable volume rendering shader Smart management of volumes in GPU memory Possibility to run simple processing operations on the volume (e.g. Non-linear transforms) Consider possible complications GPU features not available / software only fallback Volumes too big to for GPU memory	Compare the architectures of different existing projects where parts of the required functionality has been implemented: Ibis Neuronav/PRISM (Multi-volume ray-casting with programmable shaders in VTK) Steve Pieper's volume processing on the GPU with OpenGL in VTK and GLSL and with WebGL (With Anna Fruehstueck) and WebGL2 (see videos below) CustusX (GPU volume slicing and compositing with multi-window context sharing) Determine a sensible way to integrate all those contribution in VTK.	TODO

Illustrations

3D Image Filters in WebGL2

Multivolume rendering and nonlinear transforms in WebGL2

Background and References

Some notes about sharing GLSL code between desktop OpenGL and WebGL

Schott M, Pascal Grosset AV, Martin T, Pegoraro V, Smith ST, Hansen CD. Depth of Field Effects for Interactive Direct Volume Rendering. Comput Graph Forum. 2011 Jun;30(3):941–50.

Volumetric shadows and light scattering:

Kniss J, Premoze S, Hansen C, Shirley P, McPherson A. A model for volume lighting and modeling. IEEE Trans Vis Comput Graph. 2003;9(2):150–62.

Ambiant occlusion (this one should be possible to do with ray casting, but not as efficient):

Hernell F, Ljung P, Ynnerman A. Local Ambient Occlusion in Direct Volume Rendering. IEEE Trans Vis Comput Graph. 2010 Jul;16(4):548–59.

Planning hangout June 13

(Simon, Jc, Alvaro, Sankhesh, Steve, Hina)

Recent features in VTK Volume Rendering (in master, blog post coming)

• Volume peeling - translucent geometry with volumes in GPU ray cast mapper
• Render to texture
• 2D lookup tables (value and gradient magnitude)

Work in progress

• Overlapping volumes - multiple inputs to mapper
• vtk charts to work with 2D transfer functions

Slicer to migrate to latest version once cmake hierarchy is sorted out (Jc)

Questions / discussion points:

• Ray cast vs view aligned plane-based algorithms
  • depth of focus, shadows, diffuse lighting...
  • How to integrate multiple features
• Nonlinear transformation
• Custom shaders
• Dynamic shader generation in python
• multiple components
  • RGBA
  • Independent components?
• 2D lookup tables
• Volumes that live on the GPU
  • sharing across contexts
  • use as input textures and render targets
  • tiling?
  • streaming?
• Large volumes?
• Mesa backend?
  • Offscreen support for OpenGL2 backend should work in VTK now