hello i am new to QT.How can i make window and widget background color transparent or nothing.

i couldn't understand please help me

Qt Code: 
  1. http://doc.trolltech.com/qq/qq16-background.html
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i searched the net but found no result

i found this

Qt Code: 
  1. setWindowOpacity()
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but i hear that it will not support on all video cards and even if i try to set it it hides my entire widgets

please help me.Thanks!