translucent widgets

["akshay kumar" <akshayx_ee rediffmail com>]

HI,
I searched the api's of GDK and GTK both , but couldnt locate any functionality which wud enable me to set 
the alpha channel for the background of a given widget, actually i wud like my whole application to be 
translucent (once that is done i may implement a slider to control the opacity ).
i looked at the GDKColor, it doesnt have any field for alpha channel,all i cud find was r,g,b,
the GtkColorSelection has 'get' and 'set' alpha functions,  from that i thought that somewhere in gtk setting 
of alpha must be supported. or is it there just for the future implementation of alpha channel in GDK.

if not in gtk ,is translucency effect supported in some other GUI toolkit for linux,( like Qt) ??
Thanks 
Akshay