Access the flow-field grid after applying queued affine and coord transforms.

def flow(self)->FlowField:
        "Access the flow-field grid after applying queued affine and coord transforms."
        if self._affine_mat is not None:
            self._flow = _affine_inv_mult(self._flow, self._affine_mat)
            self._affine_mat = None
            self.transformed = True
        if len(self.flow_func) != 0:
            for f in self.flow_func[::-1]: self._flow = f(self._flow)
            self.transformed = True
            self.flow_func = []
        return self._flow