[Gambas-user] how to set transparent background for buttons?

[neil lewis]

I have designed a graphic for a multifunction button for a program I am 
writing in gambas.

I want to split the graphic into it's functional parts and put those 
graphical parts onto tool buttons.
All of this is easy enough, but how can I make the bakcground colour for 
the tool buttons (or any other Gambas widget) transparent so that they 
are not restricted to rectangular shapes?