c
c@(#)  a routine to demonstrate using locator.
c
        program flocator

        character dev*20
        integer bt, BLACK, GREEN, BLUE
        real x, y, sx, sy
        logical act, curpnt
        parameter (BLACK = 0, GREEN = 2, BLUE = 4)
c
c Note the declaration of the function locator below
c
        integer locator

        print*,'Enter device name:'
        read(*,'(a)') dev

        call vinit(dev)

        call color(BLACK)
        call clear

        call color(BLUE)

c
c       draw some axes
c
        call move2(0.0, 1.0)
        call draw2(0.0, -1.0)

        call move2(1.0, 0.0)
        call draw2(-1.0, 0.0)

        call color(GREEN)

        act = .false.
        curpnt = .false.
c
c       locator returns whether a mouse button has been
c       pressed or not. In a device such as the tektronix
c       where you have to wait for a keypress to get the
c       position of the crosshairs locator returns 0
c       automatically on every second call. A return value
c       of 2 indicates the second mouse button has been pressed.
c       A return value of 1 indicates the first mouse button has
c       been pressed. We wait for the locator to return zero so
c       that we know the mouse button has been released.
c

1       continue
                bt = locator(x, y)
                if (bt .eq. -1) then
                        call vexit
                        print*,'No locator device found'
                        stop
                else if (bt .eq. 2) then
                        call vexit
                        stop
                else if (bt .eq. 0) then
                        act = .true.
                else if (act) then 
                        act = .false.
                        if (bt .eq. 1) then
                                if (curpnt) then
                                        call move2(sx, sy)
                                        call draw2(x, y)
                                        curpnt = .false.
                                else
                                        curpnt = .true.
                                end if

                                sx = x
                                sy = y
                        end if
                end if
        goto 1

        end