Thanks for your interest!
1) Yes, it is possible, and I have a GPU accelerated demo here:
http://webstaff.itn.liu.se/~stegu/JFA/
You want the version that says "validation" at the end. The other ones may not be AA at all. I'm not sure, and I don't quite remember, because that is old code that I have not touched for years. Note that the code is a few years old, so it does not use anything above GLSL 1.2: no integer indexing, no integer texture formats and no multiple render targets, and it is written using an old version of OpenGL (2.1) to be compatible with MacOS X in the version that was current back then. It still works, though, and it's fast. However, I never got around to implementing the more accurate distance measures. This demo is equivalent to "edtaafunc", without any directional dependency for the distance, it's just a linear function of the pixel value, according to equation (1) in the article.
2) Perhaps I can make this more clear: The (u,v) is the position of the "hit point" measured from the center of the pixel. The "hit point" (black circle) is the position where a line from the external point running orthogonal to the edge would hit the edge if it were at that exact distance, with the edge direction estimated from local derivatives. It that point is not within the pixel in question, the measure is not entirely reasonable, but if it's within the pixel, the "true" distance is likely to be a more accurate estimate, and is used instead.
Note that the "improvement" from the "edtaa3func" to the "edtaa4func" versions is somewhat questionable. The extra calculations improve the average accuracy, but there are corner cases at isolated pixels where they do more damage than good. You need to test it to see if it works for the kind of input images you have.
3) The "other" hint to edge direction is the direction to the closest edge pixel, which is available for pixels that are not on the edge itself. I am sorry for any confusion here. What I meant to say was that the direction to the edge pixel is a better estimate of the edge direction if the edge is far away, less accurate if the edge is close, and not applicable if the pixel is on the edge. For pixels on the edge, the derivatives is all you have. For distant pixels, the vector to the edge is a better estimate. For pixels at a distance of a few pixels or less from the edge, the derivatives may be of use to improve the estimate, but not always. I have no hard decision rule here, I can just say "it depends".
Please let me know if you have any further question. Note, however, that I am currently on vacation and may take more time than usual to respond to e-mail.
