def _applySpecialOrthoOptsCentre(centre, displayCtx, xax, yax, canvas):
    """Shared by the ``xcentre``, ``ycentre``, and ``zcentre`` functions.
    """
    xlo = displayCtx.bounds.getLo(xax)
    ylo = displayCtx.bounds.getLo(yax)
    xlen = displayCtx.bounds.getLen(xax)
    ylen = displayCtx.bounds.getLen(yax)
    xmid = xlo + 0.5 * xlen
    ymid = ylo + 0.5 * ylen
    x = xmid + 0.5 * xlen * centre[0]
    y = ymid + 0.5 * ylen * centre[1]
    canvas.centreDisplayAt(x, y)
