%N tvwind %F $MIR/src/subs/tv.for
%D Set/read current window (viewport) of a display device.
%P jm
%: tv, display
%B
      subroutine tvwind(x1, y1, x2, y2)

      implicit none
      integer x1, y1, x2, y2

  TVWIND allows the current viewport on a TV screen to be set/read.
  If the device is capable of adjusting its viewport and the input
  positions are non-zero, the viewport is set.  In both cases, the
  current viewport is returned.

  Input/Output:
    x1, y1   Coordinates of the lower left corner in TV pixels.
    x2, y2   Coordinates of the top right corner in TV pixels.

  NOTE:  x1, x2, y1, y2 should ALL be set equal to 0 if resizing is NOT
         desired (ie. just do a viewport read).
