Python reading fields issue

james.thamesview

Dear community,

is it possible that the method c4d.modules.mograph.FieldInfo.Create() is (currently) bugged ie from 2024 onwards?

As an example:
I took this script from

, (and simplified it a little)

import c4d
from c4d.modules.mograph import FieldInput, FieldInfo, FieldOutput

def fieldlist_sampling(op, doc, poslist, fields):

    pCount = len(poslist)
    sample_flags = c4d.FIELDSAMPLE_FLAG_VALUE | c4d.FIELDSAMPLE_FLAG_COLOR

    fieldInput = FieldInput(poslist, allocatedCount=pCount)
    fieldInfo = FieldInfo.Create(sample_flags, None, doc, 0, 1, fieldInput, op)
    fieldOutput = FieldOutput.Create(pCount, sample_flags)

    fields.DirectInitSampling(fieldInfo)
    samplingSuccess = fields.DirectSample(fieldInput, fieldOutput.GetBlock(), fieldInfo)
    fields.DirectFreeSampling(fieldInfo)

    return fieldOutput



def main():

    count =5                                        
    distance = 225    
    fields = op[c4d.ID_USERDATA,1]

    null = c4d.BaseObject(c4d.Onull)

    if not count:
        return null

    div = ((count-1)/2)*distance
    poslist = [c4d.Vector((distance*c)-div,0,0) for c in range(0,count)]
    samp_list = fieldlist_sampling(op, doc, poslist, fields)
    # samp_list._value


    for n,p in enumerate(poslist):
        cube = c4d.BaseObject(c4d.Ocube)
        cube.SetRelPos(p)
        value = c4d.utils.RangeMap(value=samp_list._value[n], mininput=0, maxinput=1, minoutput=20, maxoutput=150, clampval=False)
        cube[c4d.PRIM_CUBE_LEN] = c4d.Vector(value)
        cube[c4d.ID_BASEOBJECT_USECOLOR] = 2
        cube[c4d.ID_BASEOBJECT_COLOR] = samp_list._color[n]

        cube.InsertUnder(null)

    return null

It is for a python generator with a field list in user data (id=1), field list contains a linear field.
When the field is moved the cubes change size and colour, the script is not perfect, it's just to demonstrate.

The generator works on 2023 and below but not in 2024 and above
This it the running in 2023:

and this is 2025

ferdinand

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About your First Question

I can confirm that there is an issue, and there is little that you can do. This goes back to the 2024 API update and how Field sampling changed then in the C++ API. In Python, we postponed things:

Fields sampling have been reworked, however due to time constraint the next methods have not been ported and are not working, we are going to fix it in an upcoming release.

But that apparently somehow got stuck in a backlog and we never picked up on it again. I have moved this topic to the bugs section, there is nothing you can do at the moment.

Cheers,
Ferdinand

james.thamesview

Thanks for looking at this. Does this main that it is at least on the "to do" list again?
Does it still work in c++

ferdinand

Yes, we will treat it as a bug. Apparently we implemented it, but then someone disabled the implementation (probably because it caused performance issues or something like that), and then we forgot do follow up on that disabled implementation. Generally we cannot give ETA's for fixes but we try to do them in a timely fashion, i.e., within a couple of minor releases such as 2024.1, 2024.2, 2024.3, etc. I am not the dev here, so I can give even less guarantees. We will update this thread when something blocks us from fixing this in the near future.

And yes, it does work in C++. The reason why this is not working in Python is because of the C++ API changes with 2024.0. This link shows how you sample things in C++, the changes revolved around making sampling a field a const operation, i.e., an operation which does not change data on the object. Which was before not the case and now requires that mutable data to be manually passed arround as the extraData as shown in the example. The changes were carried out to speed up the core of Cinema 4D.

Cheers,
Ferdinand