External processors with digital zonal convergence adjustment?

For 3 chip projectors that do not have built in convergence adjustments that can be done to some zones of the image without affecting the other zones, I am wondering what external processors exist that can do this? HTPC programs would also be an option. Someone told me pixel shaders will work, but didn't mention if it can be done zonally or not.

If there are multiple options for this, whichever can do it with none or the least artifacts or blur added to the image would be preferred.

Note: I will get a 4K display maybe soon, maybe years from now, but for now, my displays are all 1080p, so if it turns out this feature exists, but only on old 1080p processors from 10 years ago like a Gennum (just an example) or something, well, that would work just as well!