Date: 07 May 1993 00:00:01 EST

  There are two methods.  The first method is detailed in
  ~4Dgifts/examples/grafix/world2scrn.c, which is part of the
  dev.dev_sw.giftsfull package.  It multiplies the (x,y,z) vector into
  the current modeling and projection matrixes, and uses the result to
  interpolate based on the window size and position.

  The second method uses the current cursor position as a trick and is
  much simpler.  Use cmov() to set the cursor position to the point of
  interest in world space, then call getcpos() to return the cursor
  position in screen coordinates.  Note that if your entire viewport is
  off-screen, the results are undefined and you'll have to use the
  first method.

      float x,y,z;
      short x1, y1;

      cmov (x,y,z);
      getcpos (&x1, &y1);