Window id of calling process in dll

[Jac de Lad]

Hello,
I am currently writing a DLL which creates a canvas. This canvas shall have a specific size, matching to the parent windows size. The calling program is not written in PureBasic, so I only have the handle, the same I would get from WinowID(window) in PureBasic. I need to know when the window is retired, to match the canvas. Can I do this within the DLL or am I depending on the calling program to handle this?