Open source release of the retired Unity asset PicaVoxel.

This is a slightly modified version of the final asset store release, and has been tested working on Unity 2019.4 LTS.

This source is provided as-is, with no obligation for support from myself.

I encourage reporting of issues and welcome well-structured and documented pull requests, both of which I will get to as and when I can. I stopped working on PicaVoxel due to having limited time to keep up with constantly moving goalposts, and that hasn't changed.

I may look to add folks to help manage the repo if there's sufficient interest in taking it over long-term.