XPUFixedLayout

WIDGET_API int        XPUFixedLayout(
                         XPWidgetMessage      inMessage,    
                         XPWidgetID           inWidget,    
                         intptr_t             inParam1,    
                         intptr_t             inParam2);    

This function causes the widget to maintain its children in fixed position relative to itself as it is resized. Use this on the top level ‘window’ widget for your window.