def METHOD_NAME(viewer, canvas, tag):
    objs = []
    wd, ht = viewer.get_window_size()
    SquareBox = canvas.get_draw_class('squarebox')
    Text = canvas.get_draw_class('text')
    Compound = canvas.get_draw_class('compoundobject')
    x1, y1 = wd - 20, ht // 2 + 20
    zoomin = SquareBox(x1, y1, 15, color='yellow', fill=True,
                       fillcolor='gray', fillalpha=0.5, coord='window')
    zoomin.editable = False
    zoomin.pickable = True
    zoomin.add_callback('pick-down', zoom, viewer, 1)
    objs.append(zoomin)
    x2, y2 = wd - 20, ht // 2 - 20
    zoomout = SquareBox(x2, y2, 15, color='yellow', fill=True,
                        fillcolor='gray', fillalpha=0.5, coord='window')
    zoomout.editable = False
    zoomout.pickable = True
    zoomout.add_callback('pick-down', zoom, viewer, -1)
    objs.append(zoomout)
    objs.append(Text(x1 - 4, y1 + 6, text='+', fontsize=18, color=color,
                     coord='window'))
    objs.append(Text(x2 - 4, y2 + 6, text='--', fontsize=18, color=color,
                     coord='window'))
    obj = Compound(*objs)
    obj.opaque = False
    canvas.add(obj, tag=tag)