The function port-owner
returns the port owner of the graphics port
graphics-port
.
For output-pane the owner is always the pane itself.
For pixmap-port it is the owner of the port that was used when it was made.
For metafile-port the owner can be specified by the keyword argument :owner
in the macros with-internal-metafile and with-external-metafile, otherwise it is the port itself.
For printer-port the owner can be specified by the keyword argument :owner
in with-print-job, otherwise it is the port itself.
CAPI User Guide and Reference Manual (Unix version) - 3 Aug 2017