Dear community,

We recently got a non-public support request about handling drag and drop events for a custom image control in a dialog. And while we have shown this, drag event handling, multiple times before, I thought it does not hurt to answer this publicly, as this very case - an image control - is quite common, and it does not hurt having a bit more verbose public example for it.

edit: I have updated this topic with new code and a new video, to also handle outgoing asset drag events, and talk a bit about the pros and cons of different approaches, and what you could do when not implementing a code example as I did here, and therefore have a bit more leverage room when it comes to complexity.

In general, doing all this is possible. It is just that not everything is a ready-made solution for you, where you just call a function. At some point you have to "swim" here yourself, as we cannot write your code for you, but I hope the example helps shedding some light on the probably uncessarily complicated drag handling in Cinema 4D.

Cheers,
Ferdinand

Result

Code

"""Provides an example for implementing a custom control that can generate and receive drag events.

The example implements a dialog which holds multiple "cards" (BitmapCard) that display an image
and can receive drag events. The user can drag images from the file system into these cards (file
paths) or drag texture assets from the Asset Browser into these cards. The cards can also generate
drag events themselves, e.g., when the user drags from a card, it will generate a drag event. 
Showcased (selectable via the combo box in the menu of the dialog) are three drag types:

1. File paths: Dragging a card will generate an image file path drag event, which for example could 
   be dragged into a file path field of a shader, onto an object in the viewport, or onto other 
   BitmapCard controls. The advantage of this approach is that we do not have to create
   materials or assets, but can just use the file path directly.

2. Materials: Dragging a card will generate an atom drag event, here populated with a Redshift
   material that has the texture of the card as an input. This material can then be dragged onto
   anything that accepts materials, like objects in the viewport. The disadvantage of this
   approach is that we have to create a material, and that we have to exactly define how the 
   material is constructed.

3. Assets: Dragging a card will generate an asset drag event, here populated with a texture asset
   that has the texture of the card as an input. This asset can then be dragged onto anything that
   texture accepts assets, such as an object in the viewport. The disadvantage of this
   approach is that we have to create an asset.

   - The example also showcases a variation oof this approach, where we exploit a bit how the
     texture asset drag handling works, to avoid having to create an asset.


Overview:

- BitmapCard: A user area control that can receive drag events and generate drag events itself. Here
              you will find almost all the relevant code for drag and drop handling
- BitmapStackDialog: A dialog that holds multiple BitmapCard controls and allows the user to select
                the drag type via a combo box. This dialog is the main entry point of the example
                but does not contain much relevant code itself.
"""
__author__ = "Ferdinand Hoppe"
__copyright__ = "Copyright 2025 Maxon Computer GmbH"

import os
import re

import c4d
import maxon
import mxutils

# The file types that are supported to be dragged into a BitmapCard control.
DRAG_IN_FILE_TYPES: list[str] = [".png", ".jpg", ".jpeg", ".tif"]

# A regex to check of a string (which is meant to be a path/url) already as a scheme (like file:///
# or http:///). The protocol we are mostly checking for is "asset:///", but we keep this regex generic
# to allow for other schemes as well.
RE_URL_HAS_SCHEME = re.compile("^[a-zA-Z][a-zA-Z\d+\-.]*:\/\/\/")

# A non-public core message which need when we want to properly generate asset drag events.
COREMSG_SETCOMMANDEDITMODE: int = 300001000


class BitmapCard(c4d.gui.GeUserArea):
    """Implements a control that can receive bitmap path drag events and generates drag events itself.
    """

    def __init__(self, host: "BitmapStackDialog") -> None:
        """Constructs a new BitmapCard object.
        """
        # The host dialog that holds this card. This is used to access the drag type selected in the
        # combo box of the dialog.
        self._host: BitmapStackDialog = host

        # The image file path and the bitmap that is displayed in this card.
        self._path: str | None = ""
        self._bitmap: c4d.bitmaps.BaseBitmap | None = None

    def GetMinSize(self) -> tuple[int, int]:
        """Called by Cinema 4d to evaluate the minimum size of the user area.
        """
        return 250, 100

    def DrawMsg(self, x1, y1, x2, y2, msg_ref):
        """Called by Cinema 4D to let the user area draw itself.
        """
        self.OffScreenOn()
        self.SetClippingRegion(x1, y1, x2, y2)

        # Draw the background and then the bitmap if it exists. In the real world, we would have to
        # either adapt #GetMinSize to the size of the bitmap, or draw the bitmap in a way that it
        # fits into the user area, e.g., by scaling it down. Here we just draw it at a fixed size.
        self.DrawSetPen(c4d.gui.GetGuiWorldColor(c4d.COLOR_BGGADGET))
        self.DrawRectangle(x1, y1, x2, y2)
        if self._bitmap:
            w, h = self._bitmap.GetSize()
            self.DrawBitmap(self._bitmap, 5, 5, 240, 90, 0,
                            0, w, h, c4d.BMP_NORMALSCALED)

    def Message(self, msg: c4d.BaseContainer, result: c4d.BaseContainer) -> int:
        """Called by Cinema 4D to handle messages sent to the user area.

        Here we implement receiving drag events when the user drags something onto this user area.
        """
        # A drag event is coming in.
        if msg.GetId() == c4d.BFM_DRAGRECEIVE:
            # Get out when the drag event has been discarded.
            if msg.GetInt32(c4d.BFM_DRAG_LOST) or msg.GetInt32(c4d.BFM_DRAG_ESC):
                return self.SetDragDestination(c4d.MOUSE_FORBIDDEN)

            # Get out when this is not a drag type we support (we just support images). Note that we
            # cannot make up drag types ourselves, so when we want to send/receive complex data, we
            # must use the DRAGTYPE_ATOMARRAY type and pack our data into a BaseContainer attached
            # to the nodes we drag/send.
            data: dict = self.GetDragObject(msg)
            dragType: int = data.get("type", 0)
            if dragType not in [c4d.DRAGTYPE_FILENAME_IMAGE, maxon.DRAGTYPE_ASSET]:
                return self.SetDragDestination(c4d.MOUSE_FORBIDDEN)

            # Here we could optionally check the drag event hitting some target area.
            # yPos: float = self.GetDragPosition(msg).get('y', 0.0)
            # if not 0 < yPos < 50 or not self.CheckDropArea(msg, True, True):
            #     return self.SetDragDestination(c4d.MOUSE_FORBIDDEN)

            # After this point, we are dealing with a valid drag event.

            # The drag is still going on, we just set the mouse cursor to indicate that we are
            # ready to receive the drag event.
            if msg.GetInt32(c4d.BFM_DRAG_FINISHED) == 0:
                return self.SetDragDestination(c4d.MOUSE_MOVE)
            # The drag event is finished, we can now process the data.
            else:
                # Unpack a file being dragged directly.
                path: str | None = None
                if dragType == c4d.DRAGTYPE_FILENAME_IMAGE:
                    path = data.get("object", None)
                # Unpack an asset being dragged.
                elif dragType == maxon.DRAGTYPE_ASSET:
                    array: maxon.DragAndDropDataAssetArray = data.get(
                        "object", None)
                    descriptions: tuple[tuple[maxon.AssetDescription, maxon.Url, maxon.String]] = (
                        array.GetAssetDescriptions())
                    if not descriptions:
                        # Invalid asset but we are not in an error state.
                        return True

                    # Check that we are dealing with an image asset.
                    asset: maxon.AssetDescription = descriptions[0][0]
                    metadata: maxon.BaseContainer = asset.GetMetaData()
                    subType: maxon.Id = metadata.Get(
                        maxon.ASSETMETADATA.SubType, maxon.Id())
                    if (subType != maxon.ASSETMETADATA.SubType_ENUM_MediaImage):
                        # Invalid asset but we are not in an error state.
                        return True

                    path = str(maxon.AssetInterface.GetAssetUrl(asset, True))

                if not isinstance(path, str):
                    return False  # Critical failure.

                if (dragType == c4d.DRAGTYPE_FILENAME_IMAGE and
                    (not os.path.exists(path) or
                     os.path.splitext(path)[1].lower() not in DRAG_IN_FILE_TYPES)):
                    # Invalid file type but we are not in an error state.
                    return True

                self._path = path
                self._bitmap = c4d.bitmaps.BaseBitmap()
                if self._bitmap.InitWith(path)[0] != c4d.IMAGERESULT_OK:
                    return False  # Critical failure.

                self.Redraw()  # Redraw the user area to show the new bitmap.

                return True

        # Process other messages, doing this is very important, as we otherwise break the
        # message chain.
        return c4d.gui.GeUserArea.Message(self, msg, result)

    def InputEvent(self, msg: c4d.BaseContainer) -> bool:
        """Called by Cinema 4D when the user area receives input events.

        Here we implement creating drag events when the user drags from this user area. The type of
        drag event which is initiated is determined by the drag type selected in the combo box
        of the dialog.
        """
        # When this is not a left mouse button event on this user area, we just get out without
        # consuming the event (by returning False).
        if (msg.GetInt32(c4d.BFM_INPUT_DEVICE) != c4d.BFM_INPUT_MOUSE or
                msg.GetInt32(c4d.BFM_INPUT_CHANNEL) != c4d.BFM_INPUT_MOUSELEFT):
            return False

        # Get the type of drag event that should be generated, and handle it.
        dragType: int = self._host.GetInt32(self._host.ID_DRAG_TYPE)
        return self.HandleDragEvent(msg, dragType)
    
    # --- Custom drag handling methods -------------------------------------------------------------

    # I have split up thing into three methods for readability, this all could also be done directly
    # in the InputEvent method.

    def HandleDragEvent(self, event: c4d.BaseContainer, dragType: int) -> bool:
        """Handles starting a drag event by generating the drag data and sending it to the system.

        This is called when the user starts dragging from this user area.
        """
        # This requires us to modify the document, so we must be on the main thread (technically
        # not true when the type is DRAGTYPE_FILENAME_IMAGE, but that would be for you to optimize).
        if not c4d.threading.GeIsMainThread():
            raise False

        # Generate our drag data, either a file path, a material, or an asset.
        doc: c4d.documents.BaseDocument = c4d.documents.GetActiveDocument()
        data: object = self.GenerateDragData(doc, dragType)

        # Now we set off the drag event. When we are dragging assets, we have to sandwich the event
        # in these core message calls, as otherwise the palette edit mode toggling will not work
        # correctly.
        if dragType == maxon.DRAGTYPE_ASSET:
            bc: c4d.BaseContainer = c4d.BaseContainer(
                COREMSG_SETCOMMANDEDITMODE)
            bc.SetInt32(1, True)
            c4d.SendCoreMessage(c4d.COREMSG_CINEMA, bc, 0)

        # When #HandleMouseDrag returns #False, this means that the user has cancelled the drag
        # event, one case could be that the user actually did not intend to drag, but just
        # clicked on the user area.
        #
        # In this case we remove the drag data we generated, as it is not needed anymore. Note that
        # this will NOT catch the case that the drag event is cancelled by the recipient, e.g., the
        # user drags a material onto something that does not accept materials.
        if not self.HandleMouseDrag(event, dragType, data, 0):
            self.RemoveDragData(doc, data)
            return True

        # Other half of the sandwich, we toggle the palette edit mode back to normal.
        if dragType == maxon.DRAGTYPE_ASSET:
            bc: c4d.BaseContainer = c4d.BaseContainer(
                COREMSG_SETCOMMANDEDITMODE)
            bc.SetInt32(1, False)
            c4d.SendCoreMessage(c4d.COREMSG_CINEMA, bc, 0)

        return True

    def GenerateDragData(self, doc: c4d.documents.BaseDocument, dragType
                         ) -> str | c4d.BaseMaterial | maxon.DragAndDropDataAssetArray:
        """Generates the drag data for the given drag type.

        Each tile just encapsulates a file path, but we realize dragging them as file paths,
        materials, or assets. So, when the type is material or asset, the drag data must be
        generated from the file path. Which is why we have this method here.
        """
        if not c4d.threading.GeIsMainThread():
            raise RuntimeError(
                "GenerateDragData must be called from the main thread.")

        # The user has selected "File" as the drag type, we just return the file path.
        if dragType == c4d.DRAGTYPE_FILENAME_IMAGE:
            return self._path
        # The user has selected "Material" as the drag type, we create a Redshift material with the
        # texture as input and return that material.
        elif dragType == c4d.DRAGTYPE_ATOMARRAY:
            material: c4d.BaseMaterial = mxutils.CheckType(
                c4d.BaseMaterial(c4d.Mmaterial))

            # Create a simple graph using that texture, and insert the material into the
            # active document.
            maxon.GraphDescription.ApplyDescription(
                maxon.GraphDescription.GetGraph(
                    material, maxon.NodeSpaceIdentifiers.RedshiftMaterial),
                {
                    "$type": "Output",
                    "Surface": {
                        "$type": "Standard Material",
                        "Base/Color": {
                            "$type": "Texture",
                            # Set the texture. When our source is a file we will just have a plain
                            # path, e.g. "C:/path/to/file.png" and we have to prefix with a scheme
                            # (file) to make it a valid URL. When we are dealing with an asset, the
                            # texture path will already be a valid URL in the "asset:///" scheme.
                            "Image/Filename/Path": (maxon.Url(f"{self._path}")
                                                    if RE_URL_HAS_SCHEME.match(self._path) else
                                                    maxon.Url(f"file:///{self._path}"))
                        }
                    }
                })
            doc.InsertMaterial(material)
            return [material]
        # The user has selected "Asset" as the drag type, we create a texture asset and return that.
        elif dragType == maxon.DRAGTYPE_ASSET:
            # So we have to cases here, either that we want truly want to generate an asset drag
            # event or that we just want to piggy-back onto the texture asset drag and drop
            # mechanism of Cinema 4D, which is what we do here.

            # Code for truly generating an asset drag event, where we would store the asset in the
            # scene repository.
            generateAssets: bool = False
            if generateAssets:
                # Get the scene repository and create an asset storage structure for the asset.
                repo: maxon.AssetRepository = doc.GetSceneRepository(True)
                store: maxon.StoreAssetStruct = maxon.StoreAssetStruct(
                    maxon.Id(), repo, repo)

                # Now save the texture asset to the repository.
                url: maxon.Url = maxon.Url(self._path)
                name: str = url.GetName()
                asset, _ = maxon.AssetCreationInterface.SaveTextureAsset(
                    url, name, store, (), True)

                # Create a drag array for that asset. It is important that we use the URL of the
                # asset (maxon.AssetInterface.GetAssetUrl) and not #url or asset.GetUrl(), as both
                # are physical file paths, and will then cause the drag and drop handling to use
                # these physical files, including the popup asking for wether the file should be
                # copied. We will exploit exactly this behavior in the second case.
                dragArray: maxon.DragAndDropDataAssetArray = maxon.DragAndDropDataAssetArray()
                dragArray.SetLookupRepository(repo)
                dragArray.SetAssetDescriptions((
                    (asset, maxon.AssetInterface.GetAssetUrl(asset, True), maxon.String(name)),
                ))

                return dragArray
            # With this case we can piggy-back onto the existing drag and drop texture asset
            # handling of Cinema 4D, without actually having to create an asset. THIS IS A
            # WORKAROUND, we could decide at any moment to change how the drag and drop
            # handling of assets works, possibly rendering this approach obsolete.
            else:
                # The slight disadvantage of this approach (besides it being a hack and us possibly
                # removing it at some point) is that we have to pay the download cost of
                # #self._host._dummyAssetId once. I.e., the user has to download that texture once
                # either by using it in the Asset Browser or by running this code. Once the asset has
                # been cached, this will not happen again.
                #
                # But since we search below in a 'whoever comes first' manner, what is the first
                # texture asset could change, and this could then be an asset which has not been
                # downloaded yet. So, in a more robust world we would pick a fixed asset below. But
                # this comes then with the burden of maintenance, as we could remove one of the
                # builtin texture assets at any time. So, the super advanced solution would be to
                # ship the plugin with its own asset database, and mount and use that. Here we could
                # use a hard-coded asset ID, and would have to have never pay download costs, as
                # the repository would be local.

                # Find the asset by its Id, which we have stored in the dialog.
                repo: maxon.AssetRepositoryInterface = maxon.AssetInterface.GetUserPrefsRepository()
                dummy: maxon.AssetDescription = repo.FindLatestAsset(
                    maxon.AssetTypes.File().GetId(), self._host._dummyAssetId, maxon.Id(),
                    maxon.ASSET_FIND_MODE.LATEST)

                # Setup the drag array with the asset. Note that #asset must be a valid texture
                # asset, so just passing maxon.AssetDescription() will not work. But the backend
                # for drag and drop handling will actually ignore the asset except for type checking
                # it, and use the URL we provided instead.
                dragArray: maxon.DragAndDropDataAssetArray = maxon.DragAndDropDataAssetArray()
                dragArray.SetLookupRepository(repo)
                dragArray.SetAssetDescriptions((
                    (dummy, maxon.Url(self._path), maxon.String(os.path.basename(self._path))),
                ))
            return dragArray
        else:
            raise ValueError(f"Unsupported drag type: {dragType}")

    def RemoveDragData(self, doc: c4d.documents.BaseDocument,
                       data: str | list[c4d.BaseMaterial] | maxon.DragAndDropDataAssetArray) -> bool:
        """Removes generated content when the user cancels a drag event.

        Sometimes the user starts a drag event, but then cancels it, e.g., by pressing the
        escape key. In this case, we have to remove the generated content, e.g., the material or
        asset that we created for the drag event.
        """
        if not c4d.threading.GeIsMainThread():
            return False

        if isinstance(data, list):
            # Remove the dragged materials from the document. Since we are always generating a new
            # material, we can just remove them. That is in general probably not the best design,
            # and a real world application should avoid duplicating materials.
            for item in data:
                if isinstance(item, c4d.BaseList2D):
                    item.Remove()
        elif isinstance(data, str):
            # Here we could technically remove a file.
            pass
        elif isinstance(data, maxon.DragAndDropDataAssetArray):
            # We could remove the asset, but other than for the material, there is no guarantee
            # that we are the only user of it, as the Asset API has a duplicate preventing
            # mechanism. So, the #SaveTextureAsset call above could have returned an already
            # existing asset. Since we could operate with a document bound repository, we could
            # search the whole document for asset references and only when we find none, remove
            # the asset.
            #
            # We use here the little hack that we actually do not create an asset, to just to piggy-
            # back onto the material drag and drop mechanism of assets, so we can just ignore
            # this case.
            pass

        return True


class BitmapStackDialog(c4d.gui.GeDialog):
    """Implements a a simple dialog that stacks multiple BitmapCard controls.
    """
    ID_DRAG_TYPE: int = 1002

    def __init__(self):
        """Constructs a new ExampleDialog object.
        """
        # The user area controls that will generate and receive drag events.
        self._cards: list[BitmapCard] = [
            BitmapCard(host=self) for _ in range(4)]

        # The id for the dummy asset that used to generate 'fake' texture asset drag events. We
        # search for it here once, so that we do not have to do it in the __init__ of each
        # BitmapCard, or even worse, in the HandleDragEvent of each BitmapCard.

        # We could technically also store here the AssetDescription instead of the Id, but that
        # reference can go stale, so we just store the Id and then grab with it the asset when we
        # need it. Which is much faster than searching asset broadly as we do here. In the end, we
        # could probably also do all this in the drag handling of the BitmapCard, but a little bit
        # of optimization does not hurt.
        self._dummyAssetId: maxon.Id | None = None
        if not maxon.AssetDataBasesInterface.WaitForDatabaseLoading():
            raise RuntimeError("Could not initialize the asset databases.")

        def findTexture(asset: maxon.AssetDescription) -> bool:
            """Finds the first texture asset in the user preferences repository.
            """
            # When this is not a texture asset, we just continue searching.
            meta: maxon.AssetMetaData = asset.GetMetaData()
            if (meta.Get(maxon.ASSETMETADATA.SubType, maxon.Id()) !=
                    maxon.ASSETMETADATA.SubType_ENUM_MediaImage):
                return True

            # When it is a texture asset, we store it as the dummy asset and stop searching.
            self._dummyAssetId = asset.GetId()
            return False

        # Search for our dummy asset in the user preferences repository.
        repo: maxon.AssetRepositoryInterface = maxon.AssetInterface.GetUserPrefsRepository()
        repo.FindAssets(maxon.AssetTypes.File().GetId(), maxon.Id(), maxon.Id(),
                        maxon.ASSET_FIND_MODE.LATEST, findTexture)

    def CreateLayout(self):
        """Called by Cinema 4D to populate the dialog with controls.
        """
        self.SetTitle("Drag and Drop Example")
        self.GroupSpace(5, 5)
        self.GroupBorderSpace(5, 5, 5, 5)

        # Build the combo box in the menu bar of the dialog.
        self.GroupBeginInMenuLine()
        self.GroupBegin(1000, c4d.BFH_LEFT | c4d.BFV_TOP, cols=2)
        self.GroupBorderSpace(5, 5, 5, 5)
        self.GroupSpace(5, 5)
        self.AddStaticText(1001, c4d.BFH_LEFT |
                           c4d.BFV_CENTER, name="Drag Events as:")
        self.AddComboBox(1002, c4d.BFH_RIGHT | c4d.BFV_TOP)
        self.GroupEnd()
        self.GroupEnd()

        # Add the BitmapCard controls to the dialog.
        for i, card in enumerate(self._cards):
            self.AddUserArea(2000 + i, c4d.BFH_LEFT | c4d.BFV_TOP)
            self.AttachUserArea(card, 2000 + i)

        # Add items to the combo box to select the drag type.
        self.AddChild(self.ID_DRAG_TYPE, c4d.DRAGTYPE_FILENAME_IMAGE, "Files")
        self.AddChild(self.ID_DRAG_TYPE, c4d.DRAGTYPE_ATOMARRAY, "Materials")
        self.AddChild(self.ID_DRAG_TYPE, maxon.DRAGTYPE_ASSET, "Assets")
        self.SetInt32(self.ID_DRAG_TYPE, c4d.DRAGTYPE_FILENAME_IMAGE)

        return True


# Define a global variable of the dialog to keep it alive in a Script Manager script. ASYNC dialogs
# should not be opened in production code from a Script Manager script, as this results in a
# dangling dialog. Implement a command plugin when you need async dialogs in production.
dlg: BitmapStackDialog = BitmapStackDialog()
if __name__ == "__main__":
    dlg.Open(dlgtype=c4d.DLG_TYPE_ASYNC, defaultw=150, defaulth=250)

Hi,

thanks for the kind words both from Maxon and the community. I am looking forward to my upcoming adventures with the SDK Team and Cinema community.

Cheers,
Ferdinand

Hello @holgerbiebrach,

please excuse the wait. So, this is possible in Python and quite easy to do. This new behavior is just the old dialog folding which has been reworked a little bit. I have provided a simple example at the end of the posting. There is one problem regarding title bars which is sort of an obstacle for plugin developers which want to distribute their plugins, it is explained in the example below.

I hope this helps and cheers,
Ferdinand

The result:

The code:

"""Example for a command plugin with a foldable dialog as provided with the
Asset Browser or Coordinate Manger in Cinema 4D R25.

The core of this is just the old GeDialog folding mechanic which has been
changed slightly with R25 as it will now also hide the title bar of a folded
dialog, i.e., the dialog will be hidden completely.

The structure shown here mimics relatively closely what the Coordinate Manger
does. There is however one caveat: Even our internal implementations do not
hide the title bar of a dialog when unfolded. Instead, this is done via 
layouts, i.e., by clicking onto the ≡ icon of the dialog and unchecking the
"Show Window Title" option and then saving such layout. If you would want
to provide a plugin which exactly mimics one of the folding managers, you
would have to either ask your users to take these steps or provide a layout.

Which is not ideal, but I currently do not see a sane way to hide the title
bar of a dialog. What you could do, is open the dialog as an async popup which 
would hide the title bar. But that would also remove the ability to dock the 
dialog. You could then invoke `GeDialog.AddGadegt(c4d.DIALOG_PIN, SOME_ID)`to 
manually add a pin back to your dialog, so that you can dock it. But that is 
not how it is done internally by us, as we simply rely on layouts for that.
"""

import c4d


class ExampleDialog (c4d.gui.GeDialog):
    """Example dialog that does nothing.

    The dialog itself has nothing to do with the implementation of the
    folding.
    """
    ID_GADGETS_START = 1000
    ID_GADGET_GROUP = 0
    ID_GADGET_LABEL = 1
    ID_GADGET_TEXT = 2

    GADGET_STRIDE = 10
    GADEGT_COUNT = 5

    def CreateLayout(self) -> bool:
        """Creates dummy gadgets.
        """
        self.SetTitle("ExampleDialog")
        flags = c4d.BFH_SCALEFIT

        for i in range(self.GADEGT_COUNT):
            gid = self.ID_GADGETS_START + i * self.GADGET_STRIDE
            name = f"Item {i}"

            self.GroupBegin(gid + self.ID_GADGET_GROUP, flags, cols=2)
            self.GroupBorderSpace(5, 5, 5, 5)
            self.GroupSpace(2, 2)
            self.AddStaticText(gid + self.ID_GADGET_LABEL, flags, name=name)
            self.AddEditText(gid + self.ID_GADGET_TEXT, flags)
            self.GroupEnd()
        return True


class FoldingManagerCommand (c4d.plugins.CommandData):
    """Provides the implementation for a command with a foldable dialog.
    """
    ID_PLUGIN = 1058525
    REF_DIALOG = None

    @property
    def Dialog(self) -> ExampleDialog:
        """Returns a class bound ExampleDialog instance.
        """
        if FoldingManagerCommand.REF_DIALOG is None:
            FoldingManagerCommand.REF_DIALOG = ExampleDialog()

        return FoldingManagerCommand.REF_DIALOG

    def Execute(self, doc: c4d.documents.BaseDocument) -> bool:
        """Folds or unfolds the dialog.

        The core of the folding logic as employed by the Asset Browser
        or the Coordinate manager in R25.
        """
        # Get the class bound dialog reference.
        dlg = self.Dialog
        # Fold the dialog, i.e., hide it if it is open and unfolded. In C++
        # you would also want to test for the dialog being visible with
        # GeDialog::IsVisible, but we cannot do that in Python.
        if dlg.IsOpen() and not dlg.GetFolding():
            dlg.SetFolding(True)
        # Open or unfold the dialog. The trick here is that calling
        # GeDialog::Open will also unfold the dialog.
        else:
            dlg.Open(c4d.DLG_TYPE_ASYNC, FoldingManagerCommand.ID_PLUGIN)

        return True

    def RestoreLayout(self, secret: any) -> bool:
        """Restores the dialog on layout changes.
        """
        return self.Dialog.Restore(FoldingManagerCommand.ID_PLUGIN, secret)

    def GetState(self, doc: c4d.documents.BaseDocument) -> int:
        """Sets the command icon state of the plugin.

        This is not required, but makes it a bit nicer, as it will indicate
        in the command icon when the dialog is folded and when not.
        """
        dlg = self.Dialog
        result = c4d.CMD_ENABLED
        if dlg.IsOpen() and not dlg.GetFolding():
            result |= c4d.CMD_VALUE

        return result


def RegisterFoldingManagerCommand() -> bool:
    """Registers the example.
    """
    return c4d.plugins.RegisterCommandPlugin(
        id=FoldingManagerCommand.ID_PLUGIN,
        str="FoldingManagerCommand",
        info=c4d.PLUGINFLAG_SMALLNODE,
        icon=None,
        help="FoldingManagerCommand",
        dat=FoldingManagerCommand())


if __name__ == '__main__':
    if not RegisterFoldingManagerCommand():
        raise RuntimeError(
            f"Failed to register {FoldingManagerCommand} plugin.")

Dear Community,

this question reached us via email-support in the context of C++, but I thought the answer might be interesting for other users too.

The underlying question in this case was how to project points from object or world space into the texture space of an object with UV data. I am showing here deliberately an approach that can be followed both in C++ and Python, so that all users can benefit from this. In C++ one has also the option of using VolumeData and its methods VolumeData::GetUvw or VolumeData::ProjectPoint but must then either implement a volume shader (as otherwise the volume data attached to the ChannelData passed to ShaderData::Output will be nullptr), or use VolumeData:: AttachVolumeDataFake to access ::ProjectPoint. There is however no inherent necessity to take this shader bound route as shown by the example.

Cheers,
Ferdinand

Result

The script has created a texture with red pixels for the intersection points of the rays cast from each vertex of the spline towards the origin of the polygon object. The script also created the null object rays to visualize the rays which have been cast.

raycast_texture.c4d : The scene file.

Code

You must save the script to disk before running it, as the script infers from the script location the place to save the generated texture to.

"""Demonstrates how to project points from world or object space to UV space.

This script assumes that the user has selected a polygon object and a spline object in the order
mentioned. The script projects the points of the spline object onto the polygon object and creates
a texture from the UV coordinates of the projected points. The texture is then applied to the
polygon object.

The script uses the `GeRayCollider` class to find the intersection of rays cast from the points of
the spline object to the polygon object. The UV coordinates of the intersection points are then
calculated using the `HairLibrary` class. In the C++ API, one should use maxon::
GeometryUtilsInterface::CalculatePolygonPointST() instead.

Finally, using GeRayCollider is only an example for projecting points onto the mesh. In practice,
any other method can be used as long as it provides points that lie in the plane(s) of a polygon.

The meat of the example is in the `main()` function. The other functions are just fluff.
"""

import os
import c4d
import mxutils
import uuid

from mxutils import CheckType

doc: c4d.documents.BaseDocument  # The currently active document.
op: c4d.BaseObject | None  # The primary selected object in `doc`. Can be `None`.

def CreateTexture(points: list[c4d.Vector], path: str, resolution: int = 1000) -> None:
    """Creates a texture from the given `points` and saves it to the given `path`.

    Parameters:
        path (str): The path to save the texture to.
        points (list[c4d.Vector]): The points to create the texture from.
    """
    # Check the input values for validity.
    if os.path.exists(path):
        raise FileExistsError(f"File already exists at path: {path}")
    if not path.endswith(".png"):
        raise ValueError("The path must end with '.png'.")

    # Create a drawing canvas to draw the points on.
    canvas: c4d.bitmaps.GeClipMap = CheckType(c4d.bitmaps.GeClipMap())
    if not canvas.Init(resolution, resolution, 24):
        raise MemoryError("Failed to initialize GeClipMap.")

    # Fill the canvas with white.
    canvas.BeginDraw()
    canvas.SetColor(255, 255, 255)
    canvas.FillRect(0, 0, resolution, resolution)

    # Draw the points on the canvas.
    canvas.SetColor(255, 0, 0)
    for p in points:
        x: int = int(p.x * resolution)
        y: int = int(p.y * resolution)
        x0: int = max(0, x - 1)
        y0: int = max(0, y - 1)
        x1: int = min(resolution, x + 1)
        y1: int = min(resolution, y + 1)
        canvas.FillRect(x0, y0, x1, y1)

    canvas.EndDraw()

    # Save the canvas to the given path.
    bitmap: c4d.bitmaps.BaseBitmap = CheckType(canvas.GetBitmap())
    bitmap.Save(path, c4d.FILTER_PNG)

    c4d.bitmaps.ShowBitmap(bitmap)

def ApplyTexture(obj: c4d.BaseObject, path: str) -> None:
    """Applies the texture at the given `path` to the given `obj`.
    """
    CheckType(obj, c4d.BaseObject)

    # Check the input values for validity.
    if not os.path.exists(path):
        raise FileNotFoundError(f"File does not exist at path: {path}")

    # Create a material and apply the texture to it.
    material: c4d.BaseMaterial = CheckType(c4d.BaseMaterial(c4d.Mmaterial), c4d.BaseMaterial)
    obj.GetDocument().InsertMaterial(material)

    shader: c4d.BaseShader = CheckType(c4d.BaseShader(c4d.Xbitmap), c4d.BaseShader)
    shader[c4d.BITMAPSHADER_FILENAME] = path
    material.InsertShader(shader)
    material[c4d.MATERIAL_COLOR_SHADER] = shader
    material[c4d.MATERIAL_PREVIEWSIZE] = c4d.MATERIAL_PREVIEWSIZE_1024

    # Apply the material to the object.
    tag: c4d.TextureTag = CheckType(obj.MakeTag(c4d.Ttexture))
    tag[c4d.TEXTURETAG_PROJECTION] = c4d.TEXTURETAG_PROJECTION_UVW
    tag[c4d.TEXTURETAG_MATERIAL] = material

def CreateDebugRays(spline: c4d.SplineObject, p: c4d.Vector) -> None:
    """Adds spline objects to the document to visualize the rays from the given `p` to the points of
    the given `spline`.
    """
    doc: c4d.documents.BaseDocument = CheckType(spline.GetDocument(), c4d.documents.BaseDocument)
    rays: c4d.BaseObject = c4d.BaseObject(c4d.Onull)
    rays.SetName("Rays")
    doc.InsertObject(rays)

    for q in spline.GetAllPoints():
        ray: c4d.SplineObject = c4d.SplineObject(2, c4d.SPLINETYPE_LINEAR)
        ray.SetPoint(0, p)
        ray.SetPoint(1, q * spline.GetMg())
        ray.Message(c4d.MSG_UPDATE)
        ray.InsertUnder(rays)

def main() -> None:
    """Carries out the main logic of the script.
    """
    # Check the object selection for being meaningful input.
    selected: list[c4d.BaseObject] = doc.GetActiveObjects(c4d.GETACTIVEOBJECTFLAGS_SELECTIONORDER)
    if (len(selected) != 2 or not selected[0].CheckType(c4d.Opolygon) or
        not selected[1].CheckType(c4d.Ospline)):
        raise ValueError("Please select a polygon object and a spline object.")

    polygonObject, splineObject = selected

    # Get the uvw tag, the points, and the polygons of the polygon object.
    uvwTag: c4d.UvwTag = mxutils.CheckType(polygonObject.GetTag(c4d.Tuvw))
    points: list[c4d.Vector] = [polygonObject.GetMg() * p for p in polygonObject.GetAllPoints()]
    polys: list[c4d.CPolygon] = polygonObject.GetAllPolygons()

    # We are casting here in a dumb manner towards the center of the polygon object. In practice,
    # one should cast rays towards the plane of the polygon object. Or even better, use another
    # method to project the points onto the polygon object, as GeRayCollider is not the most 
    # efficient thing in the world.
    rayTarget: c4d.Vector = polygonObject.GetMg().off
    CreateDebugRays(splineObject, rayTarget)

    # Initialize the GeRayCollider to find the intersection of rays cast from the points of the
    # spline object to the polygon object.
    collider: c4d.utils.GeRayCollider = c4d.utils.GeRayCollider()
    if not collider.Init(polygonObject):
        raise MemoryError("Failed to initialize GeRayCollider.")


    # Init our output list and iterate over the points of the spline object.
    uvPoints: list[c4d.Vector] = []
    for p in splineObject.GetAllPoints():

        # Transform the point from object to world space (q) and then to the polygon object's space
        # (ro). Our ray direction always points towards the center of the polygon object.
        q: c4d.Vector = splineObject.GetMg() * p
        ro: c4d.Vector = ~polygonObject.GetMg() * q
        rd: c4d.Vector = rayTarget - ro

        # Cast the ray and check if it intersects with the polygon object.
        if not collider.Intersect(ro, rd, 1E6) or collider.GetIntersectionCount() < 1:
            continue
        
        # Get the hit position and the polygon ID of the intersection.
        hit: dict = collider.GetNearestIntersection()
        pos: c4d.Vector = mxutils.CheckType(hit.get("hitpos", None), c4d.Vector)
        pid: int = mxutils.CheckType(hit.get("face_id", None), int)

        # One mistake would be now to use the barycentric coordinates that are in the intersection
        # data, as Cinema uses an optimized algorithm to interpolate in a quad and not the standard
        # cartesian-barycentric conversion. In Python these polygon weights are only exposed in a 
        # bit weird place, the hair library. In C++ these barycentric coordinates make sense because
        # there exist methods to convert them to weights. In Python the barycentric coordinates are
        # pretty much useless as we do not have such a conversion function here.

        # Compute the weights s, t for the intersection point in the polygon.
        s, t = c4d.modules.hair.HairLibrary().GetPolyPointST(
            pos, points[polys[pid].a], points[polys[pid].b],
                 points[polys[pid].c], points[polys[pid].d], True)

        # Get the uv polygon and bilinearly interpolate the coordinates using the weights. It would
        # be better to use the more low-level variable tag data access functions in VariableTag 
        # than UvwTag.GetSlow() in a real-world scenario.
        uvw: list[c4d.Vector] = list(uvwTag.GetSlow(pid).values())
        t0: c4d.Vector = c4d.utils.MixVec(uvw[0], uvw[1], s)
        t1: c4d.Vector = c4d.utils.MixVec(uvw[3], uvw[2], s)
        uv: c4d.Vector = c4d.utils.MixVec(t0, t1, t)

        # Append the UV coordinates to the output list.
        uvPoints.append(uv)

    # Write the UV coordinates to a texture and apply it to the polygon object.
    path: str = os.path.join(os.path.dirname(__file__), f"image-{uuid.uuid4()}.png")
    CreateTexture(uvPoints, path, resolution=1024)
    ApplyTexture(polygonObject, path)

    c4d.EventAdd()


if __name__ == '__main__':
    main()

Hi,

that your script is not working has not anything to do with pseudo decimals, but the fact that you are treating numbers as strings (which is generally a bad idea) in a not very careful manner. When you truncate the string representation of a number which is represented in scientific notation (with an exponent), then you also truncate that exponent and therefor change the value of the number.

To truncate a float you can either take the floor of my_float * 10 ** digits and then divide by 10 ** digits again or use the keyword round.

data = [0.03659665587738824,
        0.00018878623163019122,
        1.1076812650509394e-03,
        1.3882258325566638e-06]

for n in data:
    rounded = round(n, 4)
    floored = int(n * 10000) / 10000
    print(n, rounded, floored)

0.03659665587738824 0.0366 0.0365
0.00018878623163019122 0.0002 0.0001
0.0011076812650509394 0.0011 0.0011
1.3882258325566637e-06 0.0 0.0
[Finished in 0.1s]

Cheers
zipit

Dear community,

We will have to touch multiple parts of developers.maxon.net on the 18.01.2024 and 19.01.2024 22.01.2024. This will result in outages of our documentation and the forum these days. I will try to keep the outage times to a minimum and it will certainly not span the whole two days. But especially one task I will do on Friday might take hours to complete and I can only do that on a forum which is in maintenance mode.

Please make sure to download a recent offline documentation in case you plan to do extended development work the next two days. As a result, forum support might also be delayed on these days.

Cheers,
Ferdinand

Hi,

as @Cairyn said the problem is unreachable code. I also just saw now that you did assign the same ID to all your buttons in your CreateLayout(). Ressource and dialog element IDs should be unique. I would generally recommend to define your dialogs using a resource, but here is an example on how to do it in code.

BUTTON_BASE_ID = 1000
BUTTON_NAMES = ["Button1", "Button2", "Button3", "Button4", "Button5"]
BUTTON_DATA = {BUTTON_BASE_ID + i: name for i, name in enumerate(BUTTON_NAMES)}

class MyDialog(gui.GeDialog):

    def CreateLayout(self):
        """
        """
        self.GroupBegin(id=1013, flags=c4d.BFH_SCALEFIT, cols=5, rows=4)
        for element_id, element_name in BUTTON_DATA.items():
            self.AddButton(element_id, c4d.BFV_MASK, initw=100, 
                           name=element_name)
        self.GroupEnd()
        return True

    def Command(self, id, msg):
        """
        """
        if id == BUTTON_BASE_ID:
            print "First button has been clicked"
        elif id == BUTTON_BASE_ID + 1:
            print "Second button has been clicked"
        # ...
        if id in BUTTON_DATA.keys(): # or just if id in BUTTON_DATA
            self.Close()
        return True

Dear development community,

On September the 10th, 2024, Maxon Computer released Cinema 4D 2025.0.0. For an overview of the new features of Cinema 4D 2025.0, please refer to the release announcement. Alongside this release, a new Cinema 4D SDK and SDK documentation have been released, reflecting the API changes for 2025.0.0. The major changes are:

C++ API

• What was formerly has been know as the Classic API has been deprecated in favour of the Cinema API. Alongside this a new cinema namespace has been introduced which contains all the entities which were formerly in the anonymous global namespace known as the Classic API. Plugin authors must adopt their code to this new API, although the changes are not nearly as extensive as for 2024. See the 2025 migration guide for details. Code examples and documentation have been updated to now refer to a Cinema API.
• 2025 uses OCIO as the default color management mode, brings an improved color picker, and made general improvements to the consistency of the OCIO implementation. This had some effects on the underlying OCIO API which are reflected in two new code examples in the OCIO Manual and a new plugin in the SDK.

Python API

• Python also received the update from Classic to Cinema API. But here the change was more of a cosmetic nature confined to the documentation. The c4d package remains the home for all formerly Classic and now Cinema API entities.
• The mxutils package received updates around standardized scene traversal, random number generation, and more.
• Graph descriptions now support variadic ports of arbitrary complexity and explicit port references.

Head to our download section for the newest SDK downloads, or the C++ and Python API change notes for an in detail overview of the changes.

We discovered late in the cycle bugs in the Asset API code examples and OCIO code in the Python SDK. Which is why the publication of the Python SDK and GitHub code examples has been postponed until these bugs are fixed. They should be ready latest by Friday the 13th of September. But the Python online documentation is accessible and error free (to our knowledge).

We had to make some last minute changes to the C++ SDK regarding OCIO code examples. Only the extended C++ SDK contains these changes. The application provided sdk.zip will catch up with the next release of Cinema 4D.

Happy rendering and coding,
the Maxon SDK Team

Cloudflare unfortunately still does interfere with our server cache. And you might have to refresh your cache manually.

When you are not automatically redirected to the new versions, and also do not see 2024.5 in the version selector, please press CTRL + F5 or press CTRL and click on the reload icon of your browser anywhere on developers.maxon.net/docs/ to refresh your cache. You only have to do this once and it will apply to all documentations at once. Otherwise your cache will automatically update latest by 19/07/2024 00:00.

Hi,

sorry for all the confusion. You have to pass actual instances of objects. The following code does what you want (and this time I actually tried it myself ;)).

import c4d

def main():
    """
    """
    bc = doc.GetAllTextures(ar=doc.GetMaterials())
    for cid, value in bc:
        print cid, value

if __name__=='__main__':
   main()

Cheers,
zipit

Dear development community,

On June the 18th, 2025, Maxon Computer released Cinema 4D 2025.3.0. For an overview of the new features of Cinema 4D 2025.3.0, please refer to the 2025.3.0 release notes. Alongside this release, a new Cinema 4D SDK and SDK documentation have been released, reflecting the API changes for 2025.3.0. The major changes are:

C++ API

• After the introduction of the CMake build system generator in Cinema 4D 2025.2.0, the C++ SDK now only supports CMake as its build system generator. The Legacy Build System is no longer supported. When you have not yet switched to CMake, please refer to our Build Systems manual for more information on how to switch to CMake.
• Updated the required Windows SDK version to Windows 10 SDK 10.0.20348.0. You might have to update Visual Studio and install the SDK via the Visual Studio installer app.

Python API

In 2025.3.0, there is a critical issue with c4dpy that will cause it to halt indefinitely when run for the first time. See the c4dpy manual for an explanation and workaround. This issue will be fixed with a hotfix for 2025.3.0.

• Added features to c4d.documents.BatchRender class, to have more control over render settings, cameras, and takes for a given job.
• Added a suite of new code examples around the subject of dialogs, including both simple beginner examples, as well as more complex examples covering subjects such as dynamic GUIs, value and layout persistence, and using resources to define dialogs and string translations. The new examples all begin with the prefix py-cmd_gui_, see our plugin examples overview for details.

Head to our download section to grab the newest SDK downloads, or read the C++ or Python API change notes for an in detail overview of the changes.

Happy rendering and coding,
the Maxon SDK Team

Cloudflare unfortunately still does interfere with our server cache. You might have to refresh your cache manually to see new data when you read this posting within 24 hours of its release.

Hey @lionlion44,

Thank you for reaching out to us. I doubt that this will not work in Python, it is just that we have not documented the symbols there yet. But you can find them in the C++ docs:

I.e., it will be c4d.FORMAT_USDIMPORT and c4d.FORMAT_USDEXPORT.

Cheers,
Ferdinand

Hey @alcol68,

so, I spent some time with this today, and both the Xpresso and Layer Shader API drive me nuts every time I have to deal with them. The TLDR is here that both Xpresso and the Layer Shader are irregular in their implementations, especially in regards to how they store and access parameters.

Find below some narrative code which guides you through all of this.

Cheers,
Ferdinand

Result

The setup expects a material to be selected which has a layer shader in its color channel with a singular transform layer in it. It will then create this Xpresso setup which drives the angle of the transform layer with a user data field in the null object holding the Xpresso setup.

edit: lol, now I see that also the first example is working in my own screenshot. I have absolutely no idea why. I would still stay away from this. The layer shader internals are a mess.

Code

"""Explores concepts around driving layer shader parameters from XPresso.

This script assumes that the active material has a layer shader in its color channel. As explained 
below, this code assumes the ID of the first parameter of the first layer in the shader, which does 
not seem to be entirely deterministic.

When push comes to shove, you might have to comment out #Solution.InternalLayerShaderAccess(...) in
#Solution.main() when it throws errors on your system.
"""

import c4d
import mxutils

from c4d.modules.graphview import GvNodeMaster, GvNode, GvPort, XPressoTag
from mxutils import CheckType

doc: c4d.documents.BaseDocument  # The currently active document.
op: c4d.BaseObject | None  # The primary selected object in `doc`. Can be `None`.

class Solution:
    """Provides a dummy class so that we can organize our code in a more readable way.
    """
    @staticmethod
    def main() -> None:
        """Called by Cinema 4D when the script is being executed.
        """
        # Get the first material and get its color channel shader, assuming it is a layer shader.
        material: c4d.BaseMaterial = CheckType(doc.GetActiveMaterial())
        shader: c4d.BaseShader = CheckType(material[c4d.MATERIAL_COLOR_SHADER], c4d.LayerShader)

        # Create the XPresso setup used by both examples below and also already add the user data
        # field to the null object used by the second example.
        null: c4d.BaseObject = CheckType(c4d.BaseObject(c4d.Onull))
        doc.InsertObject(null)

        # Create the "Angle" user data field on the null object.
        bc: c4d.BaseContainer = c4d.GetCustomDataTypeDefault(c4d.DTYPE_REAL)
        bc[c4d.DESC_NAME] = "Angle"
        bc[c4d.DESC_UNIT] = c4d.DESC_UNIT_DEGREE
        null.AddUserData(bc)
        null[c4d.ID_USERDATA, 1] = c4d.utils.DegToRad(42.0) # Initial value.

        # Create the XPresso setup.
        tag: XPressoTag = CheckType(null.MakeTag(c4d.Texpresso))
        master: GvNodeMaster = CheckType(tag.GetNodeMaster())

        # Call this first example, you might have to comment this out, as it relies on the discussed
        # magic numbers.
        Solution.InternalLayerShaderAccess(shader, master)
        # Call the second example, which uses a Python node to access the layer shader. This will
        # always work.
        Solution.PythonNodeLayerShaderAccess(shader, null, master)

        c4d.EventAdd()

    @staticmethod
    def InternalLayerShaderAccess(
            shader: c4d.BaseShader, master: GvNodeMaster) -> None:
        """Explores the internal structure of the layer shader data type and how it interfaces with 
        XPresso.

        Args:
            shader: The layer shader to inspect.
            master: The node master of the XPresso tag.
        """
        # You claimed on the forum that this ID worked for you for animating the transform angle of
        # a layer shader.
        #
        # c4d.DescID(c4d.DescLevel(c4d.SLA_LAYER_BLEND), c4d.DescLevel(10120, c4d.DTYPE_REAL))

        # Even when we ignore the concrete numeric offset and replace it with our own, it still does
        # not work for me. Could it be that you used abstracted GeListNode.__set/getitem__ access 
        # instead, i.e., what the console drag and drop generates? Because there this works for me.
        print(shader[c4d.SLA_LAYER_BLEND, 10060])

        # The problem with these IDs is that they are not deterministic from a public API point of
        # view. What holds true, is that data will placed with a stride of 20 (i.e., with 
        # BLEND_DATA_STEP_SIZE) and starts in theory at 10000 (BLEND_DATA_OFFSET). 
        # 
        # But the elements in a layer then do not follow the symbols exposed in the C++ API for the 
        # layer abstraction but are rather just sequentially numbered on a per layer type basis. E.g. 
        # for the transform layer, a parameter set event looks like this:
        #
        # void BlendEffectTransform::SetParameter(Int32 lItem, const DescID &id, ...)
        # {
        #     if (lItem == 0)
        #     {
        #         m_rAngle = t_data.GetFloat();
        #         flags |= DESCFLAGS_SET::PARAM_SET;
        #     }
        #     else if (lItem == 1)
        #     {
        #         m_bMirror = t_data.GetInt32() != 0;
        #         flags |= DESCFLAGS_SET::PARAM_SET;
        #     }
        #     ...
        #
        # Where in the API the angle has actually the id LAYER_S_PARAM_TRANS_ANGLE (2000) and the 
        # mirror has the id LAYER_S_PARAM_TRANS_MIRROR (2001). So, the internal values 0 and 1 are 
        # hardcoded and absolutely ignore the public API symbols. We can of course make here the 
        # observation that PUBLIC_SYMBOL - 2000 == INTERNAL_INDEX, but there is no guarantee at all 
        # that this will always hold true.
        #
        # The bigger problem is that the the layer start index seems to be somewhat arbitrary. You 
        # normally would expect that the first layer starts at 10000 (because BLEND_DATA_OFFSET and 
        # that is what the code suggests), but this does not hold true. When I added a single 
        # transform layer, its angle parameter had most of the time the ID 10060, i.e., this first 
        # layer seems to start at what would be the third slot. Once I have also seen it starting at
        # 10040 without having a good explanation why.

        # So, internally, the layer shader is a bit irregular, or at least more complex than it looks
        # like. But let's continue for now and accept these magic numbers.

        # To more formally define the DescID for this parameter, we need to define its DescID. For 
        # that we need the data type of SLA_LAYER_BLEND. It is not exposed as a symbol in the public
        # API (but you could look up its numeric value in the description of a layer shader). So, we 
        # define it here.
        CUSTOMDATA_BLEND_LIST: int = 1011131

        # Now we can define the DescID for the transform angle parameter of the first layer. This 
        # assumes that it uses the magic number 10060 for the first property of the first layer and 
        # that it is of type float. If it is a transform layer or not does not really matter.
        did: c4d.DescID = c4d.DescID(
            # First desc level is the datatype unexposed to the public API (both C++ and Python)
            c4d.DescLevel(    
                c4d.SLA_LAYER_BLEND,   # The parameter ID for the layer blend list.
                CUSTOMDATA_BLEND_LIST, # Its data type.
                shader.GetType()),     # And the owner type of the parameter, i.e., the layer shader.
            # The sub-channel of the parameter, i.e., we reach here into the internals of the 
            # unexposed data type.
            c4d.DescLevel(             
                10060,                 # Our magic number for the first property of the first layer.
                c4d.DTYPE_REAL,        # The angle is a real number, you got that absolutely right.
                0))                    # For sub-channels, the owner type is usually 0.
        
        # With this DescID, we can now access the parameter value formally.
        if not shader.SetParameter(did, c4d.utils.DegToRad(30), c4d.DESCFLAGS_SET_NONE):
            raise RuntimeError("Could not set parameter value.")
        
        angle: float | None = shader.GetParameter(did, c4d.DESCFLAGS_GET_NONE)
        if angle is None:
            raise RuntimeError("Could not get parameter value.")

        print(f"{angle = }")

        # The bad news is that all this will not work in XPresso. The code below will run and create 
        # a port but the port is absolutely garbage, as it is a "color profile" port. But I had a 
        # look at how the C++ XPresso code creates the ports for #ID_OPERATOR_OBJECT nodes and there
        # is custom logic also covering layer shaders that is not replicable in the public API
        # (neither C++ nor Python). Which is likely why this fails with a nonsense port.

        # edit: okay, sometimes it seems to work. I would still avoid all this layer shader internals mess.

        root: GvNode = CheckType(master.GetRoot())
        objNode: GvNode = CheckType(master.CreateNode(root, c4d.ID_OPERATOR_OBJECT, x=50, y=50))
        objNode[c4d.GV_OBJECT_OBJECT_ID] = shader
        brokenAnglePort: GvPort | None = objNode.AddPort(c4d.GV_PORT_INPUT, did)
        if not brokenAnglePort:
            raise RuntimeError("Could not add port to node.")
        print(f"{brokenAnglePort = }")

    @staticmethod
    def PythonNodeLayerShaderAccess(
        shader: c4d.BaseShader, null: c4d.BaseObject,master: GvNodeMaster) -> None:
        """Creates a Python XPresso node that accesses the transform angle parameter of the first
        layer in the given layer shader.

        Args:
            shader: The layer shader to manipulate.
            null: The null object that hosts the XPresso tag and the 'Angle' user data field.
            master: The node master of the XPresso tag.
        """
        # As you said yourself, an easy way out is to use a Python node. So, let's start by creating
        # a Python node.
        root: GvNode = CheckType(master.GetRoot())
        pyNode: GvNode = CheckType(master.CreateNode(root, c4d.ID_OPERATOR_PYTHON, x=200, y=200))

        # Create a parameter description for a link box named "Shader Link" and add it as a user 
        # data field to the Python node. There are other ways to get "in" a BaseList2D into a Python
        # node, but it does not have a BaseLink port type, so we always have get a bit creative.
        # Another way could be to pass the UUID of the node, but this then always requires us 
        # searching the node which costs performance.
        bc: c4d.BaseContainer = c4d.GetCustomDataTypeDefault(c4d.DTYPE_BASELISTLINK)
        bc[c4d.DESC_NAME] = "Shader Link"
        pyNode.AddUserData(bc)

        # Now set the user data to our shader and the code to the code we define below.
        pyNode[c4d.ID_USERDATA, 1] = shader 
        pyNode[c4d.GV_PYTHON_CODE] = Solution.CODE

        # Now remove all the default ports from the node.
        ports: list[GvPort] = CheckType((pyNode.GetInPorts() or []) + (pyNode.GetOutPorts() or []))
        for p in ports:
            pyNode.RemovePort(p)

        # Now we are going to add in and output ports to the Python node. This works a bit differently
        # than for other nodes, see https://developers.maxon.net/forum/topic/16302/ for a more in 
        # depth discussion of the subject.
        angleInPort: GvPort = CheckType(pyNode.AddPort(
            c4d.GV_PORT_INPUT,
            c4d.DescID(
                c4d.DescLevel(c4d.IN_REAL, c4d.DTYPE_SUBCONTAINER, pyNode.GetType()),
                c4d.DescLevel(1000, c4d.DTYPE_REAL, 0)
            )))
        angleInPort.SetName("angle_in")
        
        angleOutPort: GvPort = CheckType(pyNode.AddPort(
            c4d.GV_PORT_OUTPUT,
            c4d.DescID(
                c4d.DescLevel(c4d.OUT_REAL, c4d.DTYPE_SUBCONTAINER, pyNode.GetType()),
                c4d.DescLevel(1000, c4d.DTYPE_REAL, 0)
            )))
        angleOutPort.SetName("angle_out")

        # Now we create nodes for the null object and a result node and connect them to the Python.
        objNode: GvNode = CheckType(master.CreateNode(root, c4d.ID_OPERATOR_OBJECT, x=50, y=100))
        resNode: GvNode = CheckType(master.CreateNode(root, c4d.ID_OPERATOR_RESULT, x=350, y=200))

        # The output port for our "Angle" user data field on the null object.
        objOutPort: GvPort | None = objNode.AddPort(
            c4d.GV_PORT_OUTPUT,
            c4d.DescID(
                c4d.DescLevel(c4d.ID_USERDATA, c4d.DTYPE_SUBCONTAINER, objNode.GetType()),
                c4d.DescLevel(1, c4d.DTYPE_REAL, 0)
            ))
        if not objOutPort:
            raise RuntimeError("Could add user data port to object node.")
        
        # A result node can only have one input port, so we can also just do this without any danger
        # that future versions of Cinema 4D might break this code. We could also be more verbose.
        resInPort: GvPort | None = resNode.GetInPorts()[0] if resNode.GetInPorts() else None
        if not resInPort:
            raise RuntimeError("Could not get input port from result node.")
        
        # And we wire everything up and are done, yay!
        objOutPort.Connect(angleInPort)
        angleOutPort.Connect(resInPort)


    # The Python code used by the second, Python node based example, to set the code of the Python
    # node.
    CODE: str = '''import c4d

op: c4d.modules.graphview.GvNode # The Python Xpresso node containing this code.

def main() -> None:
    """Sets the value of the transform angle parameter of the first layer in the linked layer 
    shader and outputs the value to the output port.
    """
    global angle_out

    try:
        shader: c4d.BaseShader = op[c4d.ID_USERDATA, 1] # The shader linked in the user data field.
        if not isinstance(shader, c4d.LayerShader):
            angle_out = 0.0
            print("The linked shader is not a layer shader.")
            return
        
        # It is of course up to you to define the details of this. My code does not make much sense.
        layer: c4d.LayerShaderLayer = shader.GetFirstLayer()
        if layer.GetType() != c4d.TypeTransform:
            angle_out = 0.0
            print("The first layer is not a transform layer.")
            return

        if not layer.SetParameter(c4d.LAYER_S_PARAM_TRANS_ANGLE, angle_in):
            angle_out = 0.0
            print("Could not set angle parameter.")
            return

        angle_out = angle_in
    except:
        angle_out = 0.0
'''


if __name__ == '__main__':
    Solution.main()

Thanks for pointing it out, changed it

Hey @alcol68,

sorry, I have not forgotten you, but I was busy with the fall release. I will have a look tomorrow. What you are doing c4d.DescLevel(10120, ...) (i.e., BLEND_DATA_OFFSET + X) is the right direction.

Xpresso is an unholy hellhole when it comes to its operator IDs and things can fail when you are not ultra precise in your DescID definitions (your DescLevel is there for example missing the creator, and Xpresso can be picky about that - everywhere else the creator usually does not matter).

Cheers,
Ferdinand

Hey @mogh,

without details from your console, this is hard to answer. The dangling sessions are well known NodeBB problem and the NodeBB team has never fully addressed it. The general consensus is that this is caused by NodeBB locking onto outdated service workers, which when you have still the site open while doing so, might even survive a cache reset.

What I would do:

1. Check if the problem exists on multiple devices and/or browsers.
2. Log out.
3. Close developers.maxon.net.
4. Remove the whole cache of developers.maxon.net.

When this does not help, I would have to see your console output to see if there are any errors being raised.

Cheers,
Ferdinand

Hey,

well, the reason for the "compiler" restrictions mentioned in the docs, is that the SDK is shipped with code example projects and precompiled static libraries for these targets. But the SDK also comes with its full source (the 'includes'), so nothing is really preventing you from using another IDE/compiler. The VS 2019 projects should also be relatively safe to upgrade to 2022. With XCode things are more complicated, and I would there recommend creating your own project from scratch instead of updating the existing one.

In the bigger picture, we probably should update the Cineware SDK to also using CMake as the Cinema 4D SDK does these days, and with that offer more flexibility. I have this on my bucket list, but it is not very high in priority, because the Cineware SDK is our least requested SDK. When you have concrete problems with creating a build system for the Cineware SDK for your desired compiler (and IDE), just post the questions here, and I will try to help you.

Cheers,
Ferdinand

Dear development community,

On September the 10th, 2025, Maxon Computer unveiled the Maxon One fall release. For an overview of the new features please refer to the video.

Alongside this release, existing APIs have been updated and new APIs have been introduced.

Cinema 4D

For a detailed overview, see the C++ SDK change notes and Python SDK change notes.

C++ API

• The biggest change for retuning developers is the all new CMake build system which has been introduced within the 2025 release cycle.
• Added Migrating to the 2026.0 API manual, providing a brief overview of the changes for returning developers.

Python API

• Added more debugging and development features in mxutils.
• Various bugfixes.

ZBrush

Python API

• Introduced new Python API for ZBrush.
• Introduced ZBrush Python online documentation and its SDK counterpart.

Head to our download section to grab the newest SDK downloads.

Happy rendering and coding,
the Maxon SDK Team

Cloudflare unfortunately still does interfere with our server cache. You might have to refresh your cache manually to see new data when you read this posting within 24 hours of its release.

Hey @datamilch,

Thank you for reaching out to us. GetRad and GetMp express the locally aligned bounding box of an object. I.e., the bounding box in the coordinate system of the object. For a world space aligned bounding box we once had this thread, the Cinema API does not offer this out of the box.

So, transforming an object will never change its bounding box. What will change the bounding box of an object, is changing its size or changing the parameters of a generator object. When you change the parameters of a generator or when your instantiate a new object, you will have to execute the passes (BaseDocument.ExecutePasses) on a document that contains the object to see the correct bounding box - or wait for the next scene update.

PS: Your script is also running illegal code. You cannot modify the active document off-main-thread. I assume the is a script for a Python generator object. Its main function runs off-main-thread and you call there your csto which in turn calls SendModelingCommand on the active document. This will all sooner or later crash.

https://developers.maxon.net/docs/py/2025_3_1/manuals/manual_threading.html#threading-information

Cheers,
Ferdinand

Hey @alcol68,

We cannot always answer right away.

A layer shader stores its layer in a data type unexposed to the Python and public C++ API (BlendDataType) in its parameter SLA_LAYER_BLEND. Which is why this abstraction with LayerShaderLayer exists.

Your code went into the right direction, as you probably have to use id decomposition ((param, sub_channel)) when you want to access such value without the layer abstraction. The issue with your code is that you do not take into account that this must be a dynamic description, i.e., you have to encode which layer you mean.

I currently do not have much time due to approaching releases and would probably only find time next week to have a closer look. Here is how the data type reroutes parameter set events internally. As you can see, it encodes both the layer and the item into a desc level. How this works exactly and if this translates to Python, I would have to find out myself.

static const Int32 BLEND_DATA_OFFSET = 10000;
static const Int32 BLEND_DATA_STEP_SIZE = 20;

Bool Foo::GetParameter(...)
{
  iBlendDataType *s = (iBlendDataType*)data;
  if (!s)
    return false;

  Int32 lID = id[0].id;
  lID -= BLEND_DATA_OFFSET;

  DescID idNew = id << 1; // push out id[0] 

  Int32 lItem = lID % BLEND_DATA_STEP_SIZE;
  Int32 lLayer = lID / BLEND_DATA_STEP_SIZE;

  //BlendLayer is what you know as LayerShaderLayer
  BlendLayer* pLayer = s->m_BlendLayers.SearchLayer(lLayer); 
  if (!pLayer)
    return false;

  pLayer->GetParameter(lItem, idNew, t_data, flags);

  return CustomDataTypeClass::GetParameter(data, id, t_data, flags);
}

Cheers,
Ferdinand

Hey @alcol68,

Welcome to the Maxon developers forum and its community, it is great to have you with us!

Getting Started

Before creating your next postings, we would recommend making yourself accustomed with our forum and support procedures. You did not do anything wrong, we point all new users to these rules.

• Forum Overview: Provides a broad overview of the fundamental structure and rules of this forum, such as the purpose of the different sub-forums or the fact that we will ban users who engage in hate speech or harassment.
• Support Procedures: Provides a more in detail overview of how we provide technical support for APIs here. This topic will tell you how to ask good questions and limits of our technical support.
• Forum Features: Provides an overview of the technical features of this forum, such as Markdown markup or file uploads.

It is strongly recommended to read the first two topics carefully, especially the section Support Procedures: How to Ask Questions.

About your First Question

Your question is a little bit ambiguous in what DescID you are looking for a layer shader, you probably mean the properties of one of its children and not the layer shader itself. I would recommend to have a look at BaseShader: Access and Structure (C++) to understand how shaders are nested. You can then check out this posting for how to manipulate a layer shader in Python where I also documented its more fringe parameters.

Cheers,
Ferdinand