Python ShellTest scene is giving a weird behavior

[julien-siguenza]

Hi there!

It seems that I experience something very weird when I try to run the ShellTest scene using the python API.

I tried to replicate the xml ShellTest scene within a python file that can be found here.

When I run this python script, the scene is launched correctly, but I then animate it and try to sollicitate the plate using the SHIFT+click interaction, and the deformation of the plate is completely crashing.

Can anyone please try to run this python script and tell me what's happening?

Maybe I am missing something obvious there 😣

FYI: @hugtalbot @bakpaul @alxbilger

[hugtalbot]

Hey @julien-siguenza

Using the script scn2Python3, I got this scene which behaves the same way than the XML example of the Shell plugin:

"""
ShellTestPython file is based on the scene: 
b'/data/Softwares/sofa/src/master'/../plugins/Shell/examples/xml/ShellTest.scn
. It has been converted into a python script compatible with the SofaPython3 plugin. 
"""

import sys
import Sofa
import SofaRuntime

def main():
        rootNode=Sofa.Core.Node("rootNode")
        createScene(rootNode)
        Sofa.Simulation.init(rootNode)

        Sofa.Gui.GUIManager.Init("myscene", "qglviewer")
        Sofa.Gui.GUIManager.createGUI(rootNode, __file__)
        Sofa.Gui.GUIManager.SetDimension(1080, 1080)
        Sofa.Gui.GUIManager.MainLoop(rootNode)
        Sofa.Gui.GUIManager.closeGUI()

if __name__ == '__main__':
        main()

def createScene(rootNode):
        # rootNode

        # rootNode/plugins
        plugins = rootNode.addChild('plugins')
        plugins.addObject('RequiredPlugin', name='Shell')
        plugins.addObject('RequiredPlugin', name='Sofa.Component.Constraint.Projective')
        plugins.addObject('RequiredPlugin', name='Sofa.Component.Engine.Select')
        plugins.addObject('RequiredPlugin', name='Sofa.Component.IO.Mesh')
        plugins.addObject('RequiredPlugin', name='Sofa.Component.LinearSolver.Direct')
        plugins.addObject('RequiredPlugin', name='Sofa.Component.Mapping.Linear')
        plugins.addObject('RequiredPlugin', name='Sofa.Component.Mass')
        plugins.addObject('RequiredPlugin', name='Sofa.Component.ODESolver.Backward')
        plugins.addObject('RequiredPlugin', name='Sofa.Component.StateContainer')
        plugins.addObject('RequiredPlugin', name='Sofa.Component.Topology.Container.Constant')
        plugins.addObject('RequiredPlugin', name='Sofa.Component.Visual')
        plugins.addObject('RequiredPlugin', name='Sofa.GL.Component.Rendering3D')
        plugins.addObject('RequiredPlugin', name='Sofa.GUI.Component')
        rootNode.addObject('AttachBodyButtonSetting', stiffness='0.1')
        rootNode.addObject('DefaultAnimationLoop')
        rootNode.addObject('VisualStyle', displayFlags='hideVisualModels hideBehaviorModels showMappings showForceFields')

        # rootNode/Square
        Square = rootNode.addChild('Square')
        Square.addObject('EulerImplicitSolver')
        Square.addObject('SparseLDLSolver', template='CompressedRowSparseMatrixMat3x3d')
        Square.addObject('MeshOBJLoader', name='loader', filename='mesh/square1.obj')
        Square.addObject('MeshTopology', name='topology', src='@loader')
        Square.addObject('MechanicalObject', template='Rigid3')
        Square.addObject('UniformMass', totalMass='0.005')
        Square.addObject('BoxROI', name='box', box='0 0.9 -0.1 1 1 0.1', drawBoxes='1')
        Square.addObject('FixedConstraint', indices='@box.indices')
        Square.addObject('TriangularBendingFEMForceField', youngModulus='1.7e3', poissonRatio='0.3', thickness='0.01')

        # rootNode/Square/Visu
        Visu = Square.addChild('Visu')
        Visu.addObject('OglModel', src='@../topology')
        Visu.addObject('IdentityMapping')

        return

Note that the MouseInteractions define a spring (with a specific stiffness, see in Edit > Mouse Manager) between a 3D point in space (your mouse) and the closest point found on the object. This is maybe not the more reliable stability test. Instead, you can use a ConstantForceField applying a known force on a known vertex of your mesh.

Let me know if this helps

[julien-siguenza]

Hi @hugtalbot,

Thank you for your feedback!

The python script you shared with me is pretty identical to the one I shared in my previous message.
I just had to apply a few modifications to make it work for me:

• Placing the if __name__ == '__main__': part at the end of the script, otherwise I get the following error message:
  
• Importing the Sofa.Gui dependency at the beginning of the script, otherwise I get the following error message:
  

These being fixed in the script you provided, I am able to run the scene and it gives me exactly the same problematic behavior that I was talking about previously.

But maybe I was not clear enough about the so-called problematic behavior I am observing here.
I think the MouseInteractions defined in this scene is perfectly appropriate to test that the plugin is operating properly, so there is no concern about that to my opinion.

What I am pointing out here is the behavior observed when I use the SHIFT+click interaction to deform the shell:

• When I am using the xml scene, the behavior of the shell looks ok in the sense that I can sollicitate the shell with many different SHIFT+click interaction and you can observe coherent deformations of the shell without any crashing.
• When I am using the python scene (either mine or yours, it doesn't matter which one), the shell is completely crashing at the first SHIFT+click interaction. When I say crashing, I mean that the shell completely disappears from the screen of the scene.

Can you please confirm me that you properly tested from your side both xml and python scenes with the SHIFT+click interaction, and that it didn't give the crash I am talking about for the python scene?

From my side, I will prepare a completely new test scene (both in xml and python) applying a bending force at the extremity of a rectangular shell, and compare the behavior observed for both scenes.
I bet this will again lead to some problematic behavior for the python scene, and perhaps it will make my point more obvious to you.

Note for you: I am using python version 3.10.14, please let me know if I should use another one.

Many thanks for your time 🙏

[julien-siguenza]

@hugtalbot please also note that:

• Both for the xml and python scenes: when I launch the scene, I get the following warnings:

• Only for the xml scene: when I launch the scene, I get the following warning:

• Both for xml and python scenes: when I animate the scene, I get the following warnings:

• Both for the xml and python scenes: when I try to deform the shell with the SHIFT+click interaction, no warning is appearing (even when the shell is crashing for the python scene).