Finger wouldn't deform in the SoftRobots/CableGripper Tutorial

[qpding]

Hi Sofa community,

I just got my hands on Sofa these few days and still in the process of going through tutorials. The "FirstSteps" tutorial works fine and is really self-explanatory, first two steps of "CableGripper" works great too. However, when it comes to "Step 3: Actuating the finger with a cable", the finger just wouldn't deform. I'm wondering if anyone can give any suggestions on this. The details are as follows:

Version

I'm using the pre-compiled binaries SOFA 19.06_with_plugins. I actually started with v21.06.03, but had problems with loading plugins and it seems that some of the tutorial materials are not done with transferring to Python3 judging from the difference between *.pyscn and *py3scn. So I figured it might be better to shift to the latest frozen Python2 version.

OS & ENV

OS: Tested on both Ubuntu 20.04.4 LTS and Debian Bookworm (Testing).
Env: conda virtual environment using Python 2.7.

Terminal output

Here's the terminal output when I launch Sofa with a tutorial scene:

❯ ./runSofa ../plugins/SoftRobots/docs/tutorials/CableGripper/details/step3.pyscn
[INFO]    [runSofa] PluginRepository paths = /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/plugins:/home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/lib
[INFO]    [runSofa] DataRepository paths = /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/share/sofa:/home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/share/sofa/examples
[INFO]    [runSofa] GuiDataRepository paths = /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/share/sofa/gui/runSofa:/home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/share/sofa/gui/qt
[INFO]    [runSofa] Loading automatically plugin list in /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/lib/plugin_list.conf
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/lib/libSofaExporter.so
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/lib/libSofaSparseSolver.so
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/lib/libSofaPreconditioner.so
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/lib/libSofaHaptics.so
[INFO]    [SofaPython] Added '/home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/lib/python2.7/site-packages' to sys.path
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/lib/libSofaPython.so
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/lib/libCImgPlugin.so
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/lib/libSofaMiscCollision.so
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/lib/libSofaDistanceGrid.so
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/lib/libSofaImplicitField.so
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/lib/libSofaAllCommonComponents.so
[INFO]    [SofaPython] Added '/home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/plugins/STLIB/python' to sys.path
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/plugins/STLIB/lib/libSTLIB.so
[INFO]    [SofaPython] Added '/home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/plugins/SoftRobots/python' to sys.path
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/plugins/SoftRobots/lib/libSoftRobots.so
[INFO]    [SofaPython] Added '/home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/plugins/SoftRobots.Inverse/python' to sys.path
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/plugins/SoftRobots.Inverse/lib/libSoftRobots.Inverse.so
[INFO]    [SofaPython] Added '/home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/plugins/ModelOrderReduction/python' to sys.path
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/plugins/ModelOrderReduction/lib/libModelOrderReduction.so
[INFO]    [PluginManager] Loaded plugin: /home/quinnd/Applications/SOFA/SOFA_v19.06.99_custom_Linux_v5.1/plugins/BeamAdapter/lib/libBeamAdapter.so
Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.
Warning: Setting a new default format with a different version or profile after the global shared context is created may cause issues with context sharing.
The constructor with a QGLFormat is deprecated, use the regular contructor instead.

[INFO]    [PythonScript] Missing RequiredPlugin SofaSparseSolver in the scene, add it from Prefab ElasticMaterialObject.
[INFO]    [SceneCheckerVisitor] Validating node "root" with checks: [SceneCheckDuplicatedName, SceneCheckMissingRequiredPlugin, SceneCheckUsingAlias]
[INFO]    [SceneCheckerVisitor] Finished validating node "root".
[WARNING] [CableConstraint(CableConstraint)] An old implementation of CableConstraint was not allowing negative force. This is now possible. However, to limit the force to be strictly positive you now have to set minForce=0.

Problem

The UI can start without a problem, showing the blue-ish mesh of the finger with the cable attached. Judging from all the INFOs it looks like that all plugins are correctly loaded. But the finger does not bend/deform when pressing +/-.

Debug trial

Plugin

My best guess is the problem comes from this line:
[INFO] [PythonScript] Missing RequiredPlugin SofaSparseSolver in the scene, add it from Prefab ElasticMaterialObject.
But I have no clue on the solution after Googling "SofaSparseSolver". Adding the following in createScene() didn't help either:

rootNode.createObject('RequiredPlugin',
            name='sparse',
            pluginName='SofaSparseSolver')

Keyboard input

Keyboard input can be confirmed to be captured by the program by adding

print(c)
print(self.cableconstraintvalue.value)

under onKeyPressed function in step3.pyscn with the following output:

[INFO]    [SofaViewer] QtViewer::keyPressEvent, CONTROL pressed
+
[[1.0]]
+
[[2.0]]
+
[[3.0]]
[INFO]    [SofaViewer] QtViewer::keyPressEvent, CONTROL pressed
-
[[2.0]]
-
[[1.0]]
-
[[0.0]]

However, no sign of deformation of the finger appeared.

My question is

How can I make the finger bend as described in the tutorial doc and video?

[EulalieCoevoet]

Hi,

Indeed the cable doesn't work in the step3. This is because the constraint solver is missing, so the cable constraint is not being solved. Try to add this on top of the scene:

    rootnode.createObject('FreeMotionAnimationLoop')
    rootnode.createObject('GenericConstraintSolver', tolerance=1e-5, maxIterations=100)

Thanks for reporting this! I've just updated the source code.

[qpding]

Thank you so much @EulalieCoevoet for the quick reply, it worked with the constraint solver. You are a life saver!