flatgen

-- So just execute the command /genmap or execute /emergeblocks (-30912,0,30927) (0,-1,0)
-- use /threads to see how many threads are assigned to mapgen
core.register_on_generated(function(minp, maxp)
    if maxp.y >= 0 and minp.y <= -1 then
        local vm, emin, emax = core.get_mapgen_object("voxelmanip")
        local data = vm:get_data()
        local area = VoxelArea:new({MinEdge=emin, MaxEdge=emax})
        local node = core.get_content_id("default:snowblock")
        for x = minp.x, maxp.x do
            for z = minp.z, maxp.z do
                data[area:index(x, 0, z)] = node
            end
        end
        vm:set_data(data)
        --vm:calc_lighting()
        vm:write_to_map()
    end
end)

core.register_chatcommand("threads",
{
    func = function()
        core.chat_send_all("num_emerge_threads: " .. core.settings:get("num_emerge_threads"))
    end,
})

local S = core.get_translator("__builtin")

local function emergeblocks_callback(pos, action, num_calls_remaining, ctx)
    if ctx.total_blocks == 0 then
        ctx.total_blocks   = num_calls_remaining + 1
        ctx.current_blocks = 0
    end
    ctx.current_blocks = ctx.current_blocks + 1

    if ctx.current_blocks == ctx.total_blocks then
        core.chat_send_player(ctx.requestor_name,
            S("Finished emerging @1 blocks in @2ms.",
                ctx.total_blocks,
                string.format("%.2f", (os.clock() - ctx.start_time) * 1000)))
    end
end

local function emergeblocks_progress_update(ctx)
    if ctx.current_blocks ~= ctx.total_blocks then
        core.chat_send_player(ctx.requestor_name,
            S("emergeblocks update: @1/@2 blocks emerged (@3%)",
            ctx.current_blocks, ctx.total_blocks,
            string.format("%.1f", (ctx.current_blocks / ctx.total_blocks) * 100)))
        core.after(2, emergeblocks_progress_update, ctx)
    end
end

core.register_chatcommand("genmap", {
    func = function(name, param)
        local context = {
            current_blocks = 0,
            total_blocks   = 0,
            start_time     = os.clock(),
            requestor_name = name
        }
        local p1 = {x=-30912,y=0,z=30927}
        local p2 = {x=0,y=-1,z=0}
        core.emerge_area(p1, p2, emergeblocks_callback, context)
        core.after(2, emergeblocks_progress_update, context)
        core.chat_send_all("num_emerge_threads: " .. core.settings:get("num_emerge_threads"))
        return true, S("Started emerge of area ranging from @1 to @2.", core.pos_to_string(p1, 1), core.pos_to_string(p2, 1))
    end,
})