In some games,particularily,in 2d game,there are some text infos display sometimes,such as when i do well,get some scores,some scores will display with fading in and fading out effect,see attachments.
so how the OGRE3D or CEGUI do it?Soryy,new in game design!What is the basic theory?
You'll have to search the segui documentation. Fading in and out is done by changing the alpha value. They should have some tutorials for you.