Gtk.CellRenderer.prototype.get_size

function get_size(widget:Gtk.Widget, cell_area:Gdk.Rectangle):void {
    // Gjs wrapper for gtk_cell_renderer_get_size()
}

Obtains the width and height needed to render the cell. Used by view widgets to determine the appropriate size for the cell_area passed to Gtk.render. If cell_area is not null, fills in the x and y offsets (if set) of the cell relative to this location.

Please note that the values set in width and height, as well as those in x_offset and y_offset are inclusive of the xpad and ypad properties.