[FFmpeg-user] question about displace filter

In the documentation for the displace filter is written: "The second input specifies how much to displace pixels along the x-axis, ..." If I understand this right, a video input file is "misused" for storing the displacement (instead of brightness). Does that mean that only positive displacements are possible? I'm looking for a solution to make curved text for a fulldome video. Thanks, Michael