title: Convert screen mouse coordinate to window coordinate
body: <p>This is continue of my previous question -> <a href="https://stackoverflow.com/questions/10823022/draw-mouse-pointer-icon">Draw mouse pointer icon?</a>
  I want to draw mouse in specific window on the desktop, i already know how to draw the mouse and how to track the movement of the real mouse.
  But i fail to convert screen coordinates, here is example what i want to do:
  When the REAL mouse is in the upper left corner 0,0 the DRAWN mouse to be in 0,0 of my specific window, and when the REAL mouse is in the down right corner 1600,900 the DRAWN mouse to be in 700,400 of my specific window.</p>
  
  <p>I will re-explain if someone is not understanding exactly the problem.</p>
  
  <p>Thanks in advance.</p>