minetest.register_on_mapgen_init(function(mgparams)
    minetest.set_mapgen_params({mgname="singlenode", flags="nolight", flagmask="nolight"})
end)

minetest.register_on_generated(function(minp, maxp, seed)
    local t1 = os.clock()
    local vm, emin, emax = minetest.get_mapgen_object("voxelmanip")
    local a = VoxelArea:new{
        MinEdge={x=emin.x, y=emin.y, z=emin.z},
        MaxEdge={x=emax.x, y=emax.y, z=emax.z},
    }

    local data = vm:get_data()

    local c_dirt  = minetest.get_content_id("default:dirt")
    local c_grass = minetest.get_content_id("default:dirt_with_grass")
    local c_water = minetest.get_content_id("default:water_source")

    local sidelen = maxp.x - minp.x + 1

    local noise = minetest.get_perlin_map(
        {offset=0, scale=1, spread={x=200, y=125, z=200}, seed=5, octaves=5, persist=0.6},
        {x=sidelen, y=sidelen, z=sidelen}
    )
    local nvals = noise:get3dMap_flat({x=minp.x, y=minp.y, z=minp.z})

    local ni = 1
    for z = minp.z, maxp.z do
    for y = minp.y, maxp.y do
    for x = minp.x, maxp.x do
        if nvals[ni] - (y - 25) / 55 > 0.5 then
            local vi = a:index(x, y, z)
            if y < 1 then
                data[vi] = c_dirt
            else
                data[vi] = c_grass
            end
        elseif y < 1 then
            local vi = a:index(x, y, z)
            data[vi] = c_water
        end
        ni = ni + 1
    end
    end
    end

    vm:set_data(data)

    vm:calc_lighting(
        {x=minp.x-16, y=minp.y, z=minp.z-16},
        {x=maxp.x+16, y=maxp.y, z=maxp.z+16}
    )

    vm:write_to_map(data)

    print(string.format("elapsed time: %.2fms", (os.clock() - t1) * 1000))
end)