Add server-less example

[lassoan]

There are many uses cases where users would not need all the features of trame, but only a simple viewer to show some results or get inputs. In these cases, it is not necessary to instantiate a server just need to set up an application logic, scene, displayable managers, etc. Quite a lot of objects need to be created and connected to even get a basic view, so it would be very useful if trame-slicer contained a serverless application, which could be started by a single command.

[lassoan]

This is an example of how much code is currently needed for setting up a serverless 3D viewer:

https://gist.github.com/lassoan/2fa7c7a02054e6b217ebfd3b33688145

[Thibault-Pelletier]

Thx for the code snippet.
Setting up a serverless viewer is actually much simpler directly using the SlicerApp class which creates all the boiler plate.

Right now the direct rendering factory is only available in the tests, but by moving the class, it should be possible to display a volume rendering with the following code:

# Create the Slicer app
slicer_app = SlicerApp()

# Instantiate a 3D view
slicer_app.view_manager.register_factory(DirectViewFactory())
threed_view = slicer_app.view_manager.create_view(ViewLayoutDefinition.threed_view())

# Load and display a volume node
volume_node = slicer_app.io_manager.load_volumes(<path to volume files>)[0]
slicer_app.display_manager.show_volume(volume_node, vr_preset="MR-Default")

# Start the VTK render window interactor
threed_view.update_size(400, 300)
threed_view.start_interactor()

[Thibault-Pelletier]

Update:

I have moved the direct factory to the library and added a minimal example for server less usage.
It has a tiny added complexity to make it tested.