An Objective-C implementation of vector based metaballs, original implementation by Hannu Kankaanpää. (http://www.niksula.hut.fi/~hkankaan/Homepages/index.html)

References:

1. http://www.niksula.hut.fi/~hkankaan/Homepages/metaballs.html
2. http://labs.byhook.com/2011/09/26/vector-metaballs/

Issues: Besides the issues highlighted in the original article by Hannu Kankaanpää,

1. Path fill errors
   In certain conditions, the generated path is not suited for rendering, it becomes obvious when using fill mode. Some way of reordering the CGPath, or removing unnecessary points is required.
2. Performance
   For better performance try using the BLAS http://www.netlib.org/blas/ or vDSP functions in Accelerate