Take a look at the existing fractal explorer in <Filters>-<Render>-<Pattern>. I think this basically does what you want. It doesn't support arbitrary functions (I bet you could code in your own if you really wanted to), but has quite a few options, and I imagine it could produce (with help from the rest of the gimp) any of the images UltraFractal can make. The author has a quick tutorial here: http://www.multimania.com/cotting/fractalexplorer_en.html (it's for an older version, but it still helps). -James Smaby
