GtkWidgetClass.getPreferredWidth

This is called by containers to obtain the minimum and natural width of a widget. A widget will never be allocated a width less than its minimum and will only ever be allocated a width greater than the natural width once all of the said widget’s siblings have received their natural widths. Furthermore, a widget will only ever be allocated a width greater than its natural width if it was configured to receive extra expand space from its parent container.

struct GtkWidgetClass
extern (C)
void function(GtkWidget* widget, int* minimumWidth, int* naturalWidth) getPreferredWidth;