title: opengl function which displays in a key callback function
body: <p>I'm using openGL using GLUT.
  I'm making my own header file with some functions.
  One of them is a rectangle where you can enter digits and save them.
  the problem here is that the if I want to know wich key is pressed, I need to put the function in de keyboardFunc callback, but I also want to display the rectangle, so I also need to put it in the display callback because you can't draw anything in the keyboard callback function.</p>
  
  <p>I can make two functions: one for to display the rectangle and one for the keys, but I want one function for both. How can I do this?</p>