write_html() in trame_vtk.tools.vtksz2html adding extra shadow close to semi transparent objects

[Felix-Alfred-Gomez]

I use write_html() inside python with pyvista using export_html (a wrapper of write_html according to the source code).

I notice extra shadow effects on semi-transparent objects when you zoom-in. I wonder if this is a bug or not, but it's an issue for my applications. Everything is described here with animation and images.

I'd be happy to have extra informations about this features, possibly a way to solve / improve this. I can provide mode details / help solving this issue if needed !

Have a nice day

[jourdain]

The issue is really related to the fact that vtk.js is not executing the same rendering code as VTK/C++. Maybe wasm could fix that specific issue, but we would need:

1. PyVista to support VTK 9.4
2. Expose the wasm view inside PyVista (mostly trivial after 1)
3. Add export capabilities to trame-vtklocal (not terribly complicated, but would need some funding/time)
4. Create a standalone JS viewer using WASM so we can look at the scene without server. (doable in a day after 3)

[jourdain]

If you want to test/validate that assumption about wasm, you can try doing some rendering with it using an example as reference.

[Felix-Alfred-Gomez]

I'm not sure about what you suggest... ! You suggest I try running an example with a view with opacity using trame-vtklocal ?

[jourdain]

What I'm suggesting is to try VTK.wasm to see if that fix that specific rendering artifact that you see with vtk.js.
If that is the case, we would need to implement those export capabilities within trame-vtklocal.

[Felix-Alfred-Gomez]

@jourdain

I did the following, as requested:

Downloaded repo then

pip install trame-vtklocal
pip install "vtk>=9.4,<9.5"

Added in trame-vtklocal\examples\vtk\cone.py

# Set opacity to make the cone semi-transparent
actor.GetProperty().SetOpacity(0.5)

Then ran :

python.exe .\trame-vtklocal\examples\vtk\cone.py

I got a semi-transparent cone without extra shading when I zoom in (as expected)

no-bug.mp4

I hope this is what you meant

[jourdain]

Thanks, I just wanted to make sure wasm was indeed going to fix your issue.

Now, like I said, we would need time or funds to help make that happen on the wasm stack.

[Felix-Alfred-Gomez]

It's not really clear how each library depend / interact with each other between vtk, trame, pyvista and wasm... When you say funding, what do you have in mind ? I made a software displaying 3D cities with topography and various data on it, and it uses pyvista for the visu. I also use trame to do an html export to share visu and results in web apps. For now I'm still in discussions with potential clients, but I could raise the funding question for an upgrade of the html visu with them.

[jourdain]

PyVista is an API on top of VTK to make things simpler/quicker. Trame is what allow VTK and PyVista to create interactive web apps with a web UI, but require a server. Technologies like vtk.js and VTK.wasm, allow to render a 3D scene locally in the browser without a server. Since trame integrate both of them, trame can extend its API to offer an "offline" version of its dynamic scene synchronization by implementing some kind of "export_to_html". While that feature exists for vtk.js, it has not been implemented with VTK.wasm. Also because VTK.wasm is more core to VTK, it could be done for plain VTK and therefore be available without requiring trame at all. If you want to discuss funding, please reach out to Kitware so we can discuss in more details.