'moves shape (selected in l, which is list ListBox of shapes)
by an offset specified in tuple delta.
Positive numbers move to (rigt, down)'

def move_shape(self, delta):

    name = self.parent.l.GetSelection()
    if (name == wx.NOT_FOUND):
        return False
    name = self.parent.l.GetString(name)
    model = self.parent.models[name]
    model.offsets = [(model.offsets[0] + delta[0]), (model.offsets[1] + delta[1]), model.offsets[2]]
    self.Refresh()
    return True
