Project Week 25/Next Generation GPU Volume Rendering
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- 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 Inc., USA Remote attendance)
- Sankhesh Jhaveri (Kitware Inc., USA Remote attendance)
|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
Compare the architectures of different existing projects where parts of the required functionality has been implemented:
Determine a sensible way to integrate all those contribution in VTK.
3D Image Filters in WebGL2
Multivolume rendering and nonlinear transforms in WebGL2
Background and References
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
- Independent components?
- 2D lookup tables
- Volumes that live on the GPU
- sharing across contexts
- use as input textures and render targets
- Large volumes?
- Mesa backend?
- Offscreen support for OpenGL2 backend should work in VTK now
Hangout at Project Week
- Attendees: Alvaro, Sankhesh, Aashish, Andras, Steve, Jc, Simon, Ole
- Open Questions:
- What is best to accomplish at Project Week?
- What architecture is best for the future and how can we get there?
- Alvero announced that volume peeling supports the OpenGL render pass, which could support custom shaders
- two calls: Prereplace and Postreplace (as in vtkPolyDataMapper)
- newer OpenGL2 version is much more flexible than the older version in OpenGL1
- allows user to replace parts of the rending process
- Need to be able to change
- per-sample ray accumulating value
- compositing function
- initialization of ray path parameters
- control over when ray terminates
- RenderPath vs RenderTags example?
- Pattern is used in the vtk volume rendering mapper
- existing implementation serves as a working example for customization
- may need to define new spots to inject code (TBD)
- Pattern to add unique identifiers to shader variables
- There are vtk hooks to help debug
- Access to compiler errors, and full shader scene
- Can use an apitrace program (linux and mac) to track opengl state
How to make it easier to customize?
- e.g. coloring samples by depth for 4D US
- high level API?
- set of worked out examples for common use cases
- At project week:
- collect examples of things that should be simple
- provide feedback and suggestions to vtk developer
- At Kitware:
- propose a high level API for feedback
- multiple overlapping volumes
- look at sharing volumes across mappers (class to represent a volume in memory)
- shared GL context (see CustusX for worked out example of a "hacked in" way to support this)
- Be able to create volume processing pipelines that connect CPU and GPU processing seemlessly
- Investigate the capabilities of vtk-m