How can I reference an object from another file?
The best way is to provide the myGLCD object as a parameter to the constructor:

touchButton::touchButton(UTFT &amp;glcddev, int x, int y, int xs, int ys, char myuse) {
  x1 = x;
  y1 = y;
  xsize = xs;
  ysize = ys;
  use = myuse;
  glcd = &amp;glcddev;
}


Then in your header you provide a:

private: 
  UTFT *glcd;


Your library code then uses the glcd pointer to the object:

glcd-&gt;drawRoundedRectangle(...);


Note the use of -&gt; since glcd is a pointer to the object (as created by the &amp; operator when it was assigned in the constructor).

Of course, as Miagma mentions, you need to ensure that anywhere that references any UTFT functions or objects has the UTFT.h header included or it won't know what you're talking about.

You can also do the same with the UTouch class - pass that object as a parameter, then each widget can have its own routine to deal with the touch events.

You can see all this kind of thing in action in the same context in the Widget class of my DisplayCore system for chipKIT boards:  


https://github.com/MajenkoLibraries/DisplayCore/blob/master/DisplayCore/DisplayCore.h#L464
https://github.com/MajenkoLibraries/DisplayCore/blob/master/DisplayCore/DisplayCore.cpp#L1587