how to display a moving object on pixmap?

["yangxiaoli" <yanggolf yeah net>]

hi:
I draw lines icons points on pixmap , it displays well, but afterward I will also display a moving icon or an object I draw on the pixmap, it means that the latter will change display position on pixmap inconstantly,but cannot affect the pixmap when it move to another position.I search the function gdk_gc_set_foreground(gc,GDK_AND) may do the effect,but I don't know how to use it. can anyone explain it ?

I really appreciated .
regards 
========================= 				
yangxiaoli
yanggolf yeah net
2003-07-20