@Swift: Nice job on the seamless texture generator!
I tried out that texture with Gimp's "Make seamless" filter and it does have the same diagonal blurry lines (of "mush" - not the texture at all) as the algorithm and BB code from the URL.
The rocks texture is a very good test, since it has huge chunky pieces to it that just don't match up at the edge. Swift's algorithm seems to be very localized to the edge of the texture, and looks like it is attempting to scale/distort the edge to minimize the "step" of the colors across the seam (there are still visible horiz/vertical seams, they're just much less noticable than the tiled original). It's definitely a complex problem... with no "easy" solution...
I tried out that texture with Gimp's "Make seamless" filter and it does have the same diagonal blurry lines (of "mush" - not the texture at all) as the algorithm and BB code from the URL.
The rocks texture is a very good test, since it has huge chunky pieces to it that just don't match up at the edge. Swift's algorithm seems to be very localized to the edge of the texture, and looks like it is attempting to scale/distort the edge to minimize the "step" of the colors across the seam (there are still visible horiz/vertical seams, they're just much less noticable than the tiled original). It's definitely a complex problem... with no "easy" solution...