The functions simple-pane-visible-height, simple-pane-visible-width, and simple-pane-visible-size can be used to read the visible geometry of a pane. Other geometrical properties of a pane can be accessed by with-geometry, which binds variables to the various geometrical properties of the pane.
CAPI User Guide and Reference Manual (Macintosh version) - 01 Dec 2021 19:31:17