This is a Quartz Composer GLSL shader patch that ray traces a Quaternion Julia set. The shader is ported from Keenan Crane's Cg version described here: devmaster.net/forums/showthread.php?t=4448

I've added a crude Ambient Occlusion addition to the shading as part of the ray tracing process is to calculate the distance to the nearest part of the fractal isosurface and so we can get an AO effect almost for free.

Without 4x super sampling I get up to 30fps @600x400 on my iMac with a NVIDIA 8800GS gfx card.

Update: see the blog post for more details and downloads: subblue.com/blog/2009/9/20/quaternion_julia

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