BaseDocument.StartPickSession() Documentation

[dskeith]

Hi,

I'm trying to work with doc.StartPickSession(callback, multi) and I'm running into some questions.

Trying this simple code...

import c4d
from c4d import gui

def OnPick(active, multi):
    print "active: ", active
    print "multi: ", multi

# Main function
def main():
    doc.StartPickSession(OnPick, multi=True)

# Execute main()
if __name__=='__main__':
    main()

I'm able to start a multi-object pick session, but once I double-click to complete it, I get this error:
TypeError: OnPick() takes exactly 2 arguments (3 given)

After a bit of detective work, it seems that adding a mystery variable to my callback function def OnPick(mystery, active, multi): fixes the error. When I run this:

import c4d
from c4d import gui

def OnPick(mystery, active, multi):
    print "mystery: ", mystery
    print "active: ", active
    print "multi: ", multi

# Main function
def main():
    doc.StartPickSession(OnPick, multi=True)

# Execute main()
if __name__=='__main__':
    main()

I get this console output:

mystery:  0
active:  [<c4d.BaseObject object called 'Cube/Cube' with ID 5159 at 0x00000290184D2B90>, <c4d.BaseObject object called 'Cube.1/Cube' with ID 5159 at 0x00000290184D2130>, <c4d.BaseObject object called 'Cube.2/Cube' with ID 5159 at 0x00000290184D2170>]
multi:  True

After a bit more detective work, it seems that mystery is 0 if I complete the pick-session by double-clicking, and it's 1 if I press Esc to finish the pick session.

Questions

1. What is the mystery variable, and what is it actually returning.
2. Is there a way to trigger a multi-pick session where the user doesn't have to hold down shift/ctrl to select multiple elements?
3. I'm noticing some weirdness in terms of which objects are selected in the Editor/Viewport after a pick session (especially if I end it by pressing Esc). What messages/redraws do I need to call after a pick session? Do I need to handle undo or will C4D?

Thanks,

Donovan

[m_adam]

Hi, Donovan thanks for reaching us.

1. The mystery variable is actually an int flag to retrieve if the user cancels the PickSession or not.

def OnPick(flags, active, multi):
    if flags & c4d.PICKSESSION_FLAG_CANCELED:
        print "User cancel"
        
    print "active: ", active
    print "multi: ", multi


def main():
    doc.StartPickSession(OnPick, multi=True)

2. No there is no way.
3. Actually nothing, it's up to you to detect when the user cancels with PICKSESSION_FLAG_CANCELED and do whatever you want. Cinema 4D handle automatically undo. But you can call BaseDocument.GetSelection before and BaseDocument.SetSelection after if the user cancels the pick session)

Finally, note the C++ version offer to adds userdata ( For more information please read the C++ documentation https://developers.maxon.net/docs/cpp/2023_2/struct_pick_session_data_struct.html)

If you have any question, please let me know.
Cheers,
Maxime.