4D fractal ray tracer filter

Tom Beddard has added another Pixel Bender filter to his blog subblue. In addition to his ports of a Droste Effect and Fractal Explorer plug-ins that work in CS4 (After Effects and Photoshop), there's now a 4D Quaternion Julia Set Ray Tracer with added ambient occlusion:

"A quaternion Julia set is a four-dimensional equivalent of the standard two-dimensional fractal. By taking a 3D 'slice' through the 4D space it is possible to visualise a solid fractal."

Quartz Composer Quaternion Julia GPU Ray Tracer with AO from subBlue on Vimeo.

There's much more detail on subblue, and also a Quartz Composer patch for the Mac OS and mention of OpenCL possibilities (already an implementation, via Satya) for future projects.