Not sure what 'Texture' is in this context. If it's OpenGL, this link might help; or this is what I'm studying myself right now.
http://www.digitalfanatics.org/projects/qt_tutorial/chapter14.html
see chapter six and seven for a simple set up.
Also, if you could elaborate a little on what you are trying to show and which events need to take place, someone would be able to help. Right now, the way I understand your code, calling show() would be the first command required to 'see' anything, but you wrote it's already visible.