A small script to convert a minetest nodebox to an obj wavefront file.

nodebox_to_wavefront.lua

-- by DS, MIT

-- Note: texture coordinates are currently completely wrong and broken

-- Please insert your nodebox here:
local input_nodebox = {
	type = "fixed",
	fixed = {-0.5, -0.5, -0.5, 0.5, 0.5, 0.5},
}

local output_filename = "out.obj"

local boxes
if input_nodebox.type == "regular" then
	boxes = {{-0.5, -0.5, -0.5, 0.5, 0.5, 0.5}}
elseif input_nodebox.type == "fixed" then
	if type(input_nodebox.fixed[1]) == "number" then
		boxes = {input_nodebox.fixed}
	else
		boxes = input_nodebox.fixed
	end
else
	error("nodebox type not supported")
end

local verts = {}
local vtexs = {}
local faces = {}

for i = 1, #boxes do
	local box = boxes[i]
	local verts_b = i*8-7
	local vtexs_b = i*12-11

	verts[verts_b+0+0+0] = {box[1], box[2], box[3]}
	verts[verts_b+1+0+0] = {box[4], box[2], box[3]}
	verts[verts_b+0+2+0] = {box[1], box[5], box[3]}
	verts[verts_b+1+2+0] = {box[4], box[5], box[3]}
	verts[verts_b+0+0+4] = {box[1], box[2], box[6]}
	verts[verts_b+1+0+4] = {box[4], box[2], box[6]}
	verts[verts_b+0+2+4] = {box[1], box[5], box[6]}
	verts[verts_b+1+2+4] = {box[4], box[5], box[6]}

	vtexs[vtexs_b+0+0+0] = {box[3], box[2]} -- x-dir (textures are upright => -y world is -y uv)
	vtexs[vtexs_b+1+0+0] = {box[6], box[2]}
	vtexs[vtexs_b+0+2+0] = {box[3], box[5]}
	vtexs[vtexs_b+1+2+0] = {box[6], box[5]}
	vtexs[vtexs_b+0+0+4] = {box[3], box[1]} -- y-dir (this is probably broken, idk how minetest orders it)
	vtexs[vtexs_b+1+0+4] = {box[6], box[1]}
	vtexs[vtexs_b+0+2+4] = {box[3], box[4]}
	vtexs[vtexs_b+1+2+4] = {box[6], box[4]}
	vtexs[vtexs_b+0+0+8] = {box[1], box[2]} -- z-dir (upright again)
	vtexs[vtexs_b+1+0+8] = {box[4], box[2]}
	vtexs[vtexs_b+0+2+8] = {box[1], box[5]}
	vtexs[vtexs_b+1+2+8] = {box[4], box[5]}

	local flen = #faces
	faces[flen+ 1] = {verts_b+0+0+0, verts_b+0+0+4, verts_b+0+2+4, vtexs_b+0+0+0, vtexs_b+1+0+0, vtexs_b+1+2+0} -- from -x
	faces[flen+ 2] = {verts_b+0+0+0, verts_b+0+2+4, verts_b+0+2+0, vtexs_b+0+0+0, vtexs_b+1+2+0, vtexs_b+0+2+0}
	faces[flen+ 3] = {verts_b+0+0+0, verts_b+1+0+0, verts_b+1+0+4, vtexs_b+0+0+8, vtexs_b+0+0+4, vtexs_b+0+0+4} -- from -y
	faces[flen+ 4] = {verts_b+0+0+0, verts_b+1+0+4, verts_b+0+0+4, vtexs_b+0+0+8, vtexs_b+0+0+4, vtexs_b+0+0+4}
	faces[flen+ 5] = {verts_b+0+0+0, verts_b+1+2+0, verts_b+1+0+0, vtexs_b+0+0+4, vtexs_b+1+2+8, vtexs_b+1+0+8} -- from -z
	faces[flen+ 6] = {verts_b+0+0+0, verts_b+0+2+0, verts_b+1+2+0, vtexs_b+0+0+4, vtexs_b+0+2+8, vtexs_b+1+2+8}
	faces[flen+ 7] = {verts_b+1+2+4, verts_b+1+0+0, verts_b+1+2+0, vtexs_b+1+2+0, vtexs_b+0+0+0, vtexs_b+0+2+0} -- from +x
	faces[flen+ 8] = {verts_b+1+2+4, verts_b+1+0+4, verts_b+1+0+0, vtexs_b+1+2+0, vtexs_b+1+0+0, vtexs_b+0+0+0}
	faces[flen+ 9] = {verts_b+1+2+4, verts_b+0+2+0, verts_b+0+2+4, vtexs_b+1+2+4, vtexs_b+0+2+4, vtexs_b+0+2+4} -- from +y
	faces[flen+10] = {verts_b+1+2+4, verts_b+1+2+0, verts_b+0+2+0, vtexs_b+1+2+4, vtexs_b+0+2+4, vtexs_b+0+2+4}
	faces[flen+11] = {verts_b+1+2+4, verts_b+0+2+4, verts_b+0+0+4, vtexs_b+1+2+8, vtexs_b+0+2+8, vtexs_b+0+0+8} -- from +z
	faces[flen+12] = {verts_b+1+2+4, verts_b+0+0+4, verts_b+1+0+4, vtexs_b+1+2+8, vtexs_b+0+0+8, vtexs_b+1+0+8}
end

local file = assert(io.open(output_filename, "w"))

do
	local verts_s = {}
	for i, v in ipairs(verts) do
		-- use %s because it produces shorter strings than %f
		verts_s[i] = string.format("v %s %s %s\n", v[1], v[2], v[3])
	end
	file:write(table.concat(verts_s))
end
do
	local vtexs_s = {}
	for i, vt in ipairs(vtexs) do
		-- use %s because it produces shorter strings than %f
		vtexs_s[i] = string.format("vt %s %s\n", vt[1], vt[2])
	end
	file:write("\n", table.concat(vtexs_s))
end
do
	local faces_s = {}
	for i, f in ipairs(faces) do
		faces_s[i] = string.format("f %d/%d %d/%d %d/%d\n", f[1], f[4], f[2], f[5], f[3], f[6])
	end
	file:write("\n", table.concat(faces_s))
end

file:close()