Inconsistency with other GUIs

[alxbilger]

I was trying to run SOFA from a Python interpreter (no runSofa). The usual way is the following code:

import Sofa
import Sofa.Gui
root = Sofa.Core.Node("root") # Generate the root node     
scene_lib.createScene(root, config) # Create the scene graph
Sofa.Simulation.init(root) # Initialization of the scene graph

Sofa.Gui.GUIManager.Init("myscene", "imgui")
Sofa.Gui.GUIManager.createGUI(root, __file__)
Sofa.Gui.GUIManager.SetDimension(1080, 1080)
Sofa.Gui.GUIManager.MainLoop(root)

But nothing happens and no GUI appears. The script ends without error.
I added the following message: #69, to find out that the root node is not given to the GUI. Hence the GUI cannot run.

In other GUIs, the root node is given to the GUI in the Sofa.Gui.GUIManager.createGUI function, via setScene. But in ImGuiGUI::CreateGUI, setScene is not called. I tried to add it, but it has side effects and it is too early for them, leading to a crash.

A workaround is to explicitly call setScene in the python script:

import Sofa
import Sofa.Gui
root = Sofa.Core.Node("root") # Generate the root node     
scene_lib.createScene(root, config) # Create the scene graph
Sofa.Simulation.init(root) # Initialization of the scene graph

Sofa.Gui.GUIManager.Init("myscene", "imgui")
Sofa.Gui.GUIManager.createGUI(root, __file__)
Sofa.Gui.GUIManager.SetDimension(1080, 1080)
Sofa.Gui.GUIManager.SetScene(root, __file__) #  <----------------------------  HERE
Sofa.Gui.GUIManager.MainLoop(root)

It would be nice to have consistency with the other GUIs.