GtkWidget::set_usize
void set_usize(int width, int height); 
    
     set_usize()  sets a widget's
     size in pixels.  Sizing methods should only be called at one level of
     the packing hierarchy; you may need to size either the container
     or its children, but doing both will create conflicts in the size
     requests made by child widgets internally, which in turn can lead
     to unexpected results.
    
    
     If you need either parameter to be ignored, use -1.
    
    
     See also:  GtkAlignment, and the packing methods
     supplied by GtkBox and 
     GtkTable.