FUNCTION wwgetzoom

;+
; WWGETZOOM
;
;   Get the zoom factor of the current window.
;
; Calling sequence
;
;   zoom = wwgetzoom()
;
; Returns the zoom factor in screen pixels per data pixel.  If the X and
; Y scales are unequal or the scale factor is not an integer, then 0
; is returned.
;-

datac_0 = convert_coord(0.,0.,/device,/to_data)
datac_1 = convert_coord(1.,1.,/device,/to_data)
xzoom = abs(1./(datac_1(0) - datac_0(0)))
yzoom = abs(1./(datac_1(1) - datac_0(1)))

xzoomi=fix(xzoom+0.5)
yzoomi=fix(yzoom+0.5)

if ((xzoomi ne yzoomi) or abs(xzoomi - xzoom) gt 1e-4) then $
    return,0 else return,xzoomi

end