Add Luanti (Minetest) schematic export

[MisterE123]

Goxel has a Luanti (formerly Minetest) palette, but no export to a minetest schematic. It would be good to be able to export schematics so that Goxel can be used as a schematic editor.

[guillaumechereau]

Thanks for letting me know. I renamed the file.

[MisterE123]

The issue was for adding schematic export

[guillaumechereau]

Sorry I wanted to close the other related issue. I guess adding an export should not be too difficult.

[MisterE123]

What will be slightly complicated is that ideally export should be defined using a text-file map of colors to node names; it should not be hardcoded, because Luanti is a game engine and each game has its own node names. It would be cool to have a MinetestGame default node mapping, but it should be easy to use/make other node mappings, both for import and export.