Instruction on how to use cliptst:

  The cube is the clipping volume, currently set to W = 1000.  The left
  mouse button rotates the viewpoint around the cube.  The middle button
  moves the triangle up (+-Y) and horizontally (+-X).  The right button
  moves the triangle horizontally (+-Z) and scales it.  Press ESC to
  quit and the space bar to dump out clip.tst, which can be loaded
  right into the points space of the rsp simulator.  The dump file
  includes the triangle data (three points) and the clipped data (
  usually four or more points).  The dump file is not generated at
  all if the triangle is not clipped (this is a bug in cliptst).