With the DK-VCL edition a user defined layer can be created via the Delphi source code. Refer to the DK-VCL sample TGIS_LayerMIF for guidance on how to create a custom layer. That sample shows both reading and writing the custom layer to disk. Also, the OpenGIS SQL vector support is an example of a user defined layer which was, of course, developed by TatukGIS.
There are constraints on the creation of a fully user defined layer with the DK-ActiveX, because customizing via Delphi source code is out of scope for the ActiveX developer. But a custom Layer can be created with the DK-ActiveX by overriding. The easiest way is to create a XGIS_LayerVector and fill it with data using the custom adaptor. This involves adding shapes and adding points to that shape. The result is not a real native format but, depending on the situation, it can be enough. Superclassing in ActiveX is not possible. Latter we might possibly add a generic DLL to the DK-ActiveX which can be compiled to support custom formats.
Another option for the ActiveX developer is to hire TatukGIS to custom develop the required user defined layer.