[SOLVED] Collision Callback function in python

[bill]

Hello,

I would like to execute a piece of code when a collision is detected, using SofaPython. From what I can tell from the API, I would want to call getCollisionPipeline() on the rootNode and then I should be able to poll getResponseList() to find out if a collision has occurred (or something along those lines).

However, to my knowledge, this can’t be done using SofaPython because the getCollisionPipeline() api call is not implemented. Is there another way to do this?

Thank you

[fedev]

Interested as well

[Hugo]

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

[tschuelia]

Hi everyone,

I’m interested in this as well. Are there any updates concerning this?

@bill757 @fedev did you manage to get something working?

Greetings
Julia

[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

[tschuelia]

Hi Hugo, sorry for the very late response.
Using a ContactListener works perfectly, thank you 🙂

[btt]

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

[Scheikl]

Hi @newbie,
please note, that there is a difference between SofaPython and the Plugin SofaPython3.

Python scripting

If you are using SofaPython3, you can add a ContactListener with

    listener = scene_node.addObject(
        "ContactListener",
        name="TestContactListener",
        collisionModel1=body1.collision.PointCollisionModel.getLinkPath(),
        collisionModel2=body2.collision.TriangleCollisionModel.getLinkPath(),
    )

This one will listen for contacts between PointCollisionModels on body1 and TriangleCollisionModels on body2.

Cheers,
Paul

[btt]

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')

[Scheikl]

Hi @newbie,
sadly I started using Sofa with SofaPython3 directly so I’ve never really used SofaPython2.

Is there an error message you could post?

Is the relative path to SkinCollision and collisionFinger correct?

Cheers,
Paul

[btt]

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

[Scheikl]

Hi @newbie,
by specifying collisionModel1 = '@skin.SkinCollision' you are not pointing to an actual collision model, but to a SofaNode that contains multiple collision models.

Try changing that to
contactlistener.createObject('ContactListener', collisionModel1 = '@skin.SkinCollision.TriangleCollisionModel', collisionModel2 = '@finger.collisionFinger.PointCollisionModel')

The object should now listen for collisions between the TriangleCollisionModel of the skin and the PointCollisionModel of finger.

Cheers,
Paul

[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

[Scheikl]

Hi @newbie,
ah the ContactListener is not in the root node, so your path misses going up one step in the tree.
You could try

contactlistener.createObject('ContactListener', collisionModel1 = '@../skin.SkinCollision.TriangleCollisionModel', collisionModel2 = '@../finger.collisionFinger.PointCollisionModel')

Cheers,
Paul

[btt]

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

[Scheikl]

Hi @newbie,
I totally missed the fact, that you gave the models a specific name, sorry. 😀
Try replacing the type of Object (TriangleCollisionModel) with the name you gave it (triangle). Same for the PointCollisionModel.

Cheers,
Paul

[btt]

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.

[Scheikl]

Hi @newbie,
I just tested the scene, and the following works fine for me:

    contactlistener.addObject(
        "ContactListener",
        collisionModel1="@/finger/collisionFinger/triangle",
        collisionModel2="@/skin/SkinCollision/point",
    )

Cheers,
Paul

[btt]

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

[Scheikl]

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

[Scheikl]

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

[Author]

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