[SOLVED] Collision Callback function in python

Hi @bill757 @fedev

Interesting point.
Two possible solutions, but at my best knowledge none have been yet implemented:
– creating a dedicated Event captured by Python when a contact really occurs (saved after the Narrow phase)
– calling a specific C++ function when a contact really occurs and binding this function in Python

@bmarques does such a question ring a bell?

Hugo

Hey @bill757 @fedev @tschuelia

I do not think a function can be directly called from Python. This I will need to check.

However, you could add a ContactListener in your simulation and at each time step using your python script read into the collision information stored in this listener.

I could create a dedicated example in the SofaPython3 plugin in the first week of 2021.

Best,

Hugo

Dear @hugo, @tschuelia
I tried to add ContactListener to my scene but It seems unproperly constructed. Could you please share the line of code to add this component?
I use sofapython to build up simulation model. Thank you for any help
Best

Thank you @scheikl, my simulation is built up using python2. So, it would be more convenient for me if your code can be converted to python2. I tried with this line but not success:
contactlistener.createObject('ContactListener', collisionModel1 = '@SkinCollision.LineCollisionModel', collisionModel2 = '@collisionFinger.LineCollisionModel')

Thank you @scheikl for following up my problem, the general structure of my scene is shown below:

def createScene(rootNode):
    ...
# Finger node
    finger = rootNode.createChild('finger')
    #collision
    collisionFinger = finger.createChild('collisionFinger')
    collisionFinger.createObject('MeshTopology', src='@loader', name='topo')
    collisionFinger.createObject('MechanicalObject', name='collisMech')
    collisionFinger.createObject('TriangleCollisionModel', name = 'triangle', 
     selfCollision=0)
    collisionFinger.createObject('LineCollisionModel', name = 'line', 
     selfCollision=False)
    collisionFinger.createObject('PointCollisionModel', name = 'point', 
    selfCollision=False)

# Skin node
    skin = rootNode.createChild('skin')
    # Collision
    skinCollision = skin.createChild('SkinCollision')
    skinCollision.createObject('MeshTopology', src='@loader', name='topology')
    skinCollision.createObject('MechanicalObject', name='collisMech')
    skinCollision.createObject('TriangleCollisionModel', name = 'triangle', 
    selfCollision=0)
    skinCollision.createObject('LineCollisionModel', name = 'line', selfCollision=0)
    skinCollision.createObject('PointCollisionModel', name = 'point', 
    selfCollision=0)
# Contact listener
    contactlistener = rootNode.createChild('contactlistener')
    contactlistener.createObject('ContactListener', collisionModel1 = '@skin.SkinCollision', collisionModel2 = '@finger.collisionFinger')

However, an error message popped up when I loaded this scene:

[ERROR]   [DAGNode(contactlistener)] Parsing Link "@skin.SkinCollision": a Data field name is specified while an object was expected.
[ERROR]   [DAGNode(contactlistener)] Parsing Link "@finger.collisionFinger": a Data field name is specified while an object was expected.
[ERROR]   [PythonScript] RuntimeError: Unable to create 'ContactListener' of type 'ContactListener' in node 'contactlistener'. Object type ContactListener<> was not created  
 The object is in the factory but cannot be created.  
Requested template : None  
Used template      : None  
Reason(s)          : Data attributes 'collisionModel1' and 'collisionModel2' are not pointing to valid collision models. 

It seems I did not set the paths for two propoerties ‘collisionModel1’ and ‘collisionModel2’. Could you (or any other suggestion will be appreciated) please point out what I did wrong? Thank you very much
Best regards,
btt

Hi @Scheikl, I did follow your construction but the same error has appeared. Hope you have another idea. Anyway, I appreciate your kind support.
Best regards,
Nhan

Hi @Scheikl, It still does not work, really weird :D. Same error appeared

Hi @Scheikl, in fact, I did it already but nothing changed :). I tried to play around with this component for the last couple of days but it is still not successful :D.

Hi @Scheikl, it is successfully added in SOFA scene. Now I am curious how to extract contact information by using python. I open up the property table of this component and see nothing (it seems wrong). Thank you for your patient.
best
btt

Hi @newbie,
you might want to check out SofaPython3.

There is a binding for the ContactListener, so you can create a ContactListener object with

`
listener = contactlistener.addObject(
“ContactListener”,
collisionModel1=”@/finger/collisionFinger/triangle”,
collisionModel2=”@/skin/SkinCollision/point”,
)
`

Now you can add any functions from the c++ code to create bindings for it.

Sadly I really do not know how to do that with SofaPython2.

Cheers,
Paul