title: OpenGL revert all transformation done by a transformation matrix
body: <p>i would like to aplly a reverse transformation matrix in a point. 
  What is it for?:
   My app (game) apply transformation into several squares objects, each one has its own transformation matrix that are applyied when drawing it. </p>
  
  <p>But i need to know if the mouse are over each object. so , for each object, I get the mouse position, and try to apply all transformations reversed. to revert the square and the mouseposition to its origin.</p>
  
  <p>If im right, this way i can compare the transformed mouse position with the object bouds.</p>
  
  <p>thw question is.. :how can i apply this reverse transformations ?
  i tried the inverse matrix, but it dosent exists all the time...</p>