Made some progress... this is transferring the image data into a FBO, and applying the shader at that time, and then using the FBO as a texture onto a plane. In principle, it should be possible to rotate/translate the plane without affecting the shader's behavior.
Integrating this into the [of.] abstractions' plumbing may have other challenges, but it looks like it may very well work.
FWIW: This is hard to figure out. Really hard. Open Frameworks doesn't do much to smooth over any rough edges in interfaces. (Even here, if I switch off the fbo, the image flips upside down.) The abstractions being discussed here are really necessary. From time to time, I hear people complain about the intense learning curve for SuperCollider, but in my experience, Open Frameworks is a million times worse. Little gotchas hiding all over the place. Every little step in this process has been literally days to work through. Ofelia is powerful, yes, but usability is not there yet.
hjh