display

Replaces every line offered to the Display Links.

It takes a list of lines, or a single text:

display.set({"Iron", "1250 ingots"})     -- two lines
display.set("Iron\n1250 ingots")          -- the same two lines
display.set({"Speed", 128, "RPM"})        -- numbers are written as text
display.set()                             -- no lines at all, like display.clear()

The limits: 16 lines and 128 characters per line. Longer lines are cut, and the values after the 16th of a list are left out. In a single text, the 16th line keeps all the rest of the text. Each value of a list becomes text the way tostring writes it.

A station departure board. A Display Board 5 blocks wide and 2 high (4 lines of 22 characters) shows the next trains. Times are Minecraft time: os.day_time() counts 1000 ticks per hour, and 0 is 6:00 in the morning. The board is built by a function, so it can be tried with a fixed time:

local DEPARTURES = {
  {time = 7500, train = "Iron Express", platform = 1},
  {time = 9000, train = "Coal Shuttle", platform = 2},
  {time = 12000, train = "Harbour Line", platform = 1},
}

local function clock(ticks)
  local t = (ticks + 6000) % 24000
  return string.format("%02d:%02d", t // 1000, t % 1000 * 60 // 1000)
end

local function board(now)
  local lines = {"Departures   " .. clock(now)}
  for _, d in ipairs(DEPARTURES) do
    if d.time >= now then
      table.insert(lines, string.format("%s %-13s P%d", clock(d.time), d.train, d.platform))
    end
  end
  return lines
end

for _, line in ipairs(board(7000)) do
  print(line)
end

Departures   13:00
13:30 Iron Express  P1
15:00 Coal Shuttle  P2
18:00 Harbour Line  P1

On the computer, the last loop becomes the program's main loop, with the real time:

while true do
  display.set(board(os.day_time()))
  sleep(5)
end

When a train has left, its line disappears and the ones below move up; the board blanks the lines left over.

See also display.line() display.clear()

Changes one line and keeps the others.

Handy when a few values change at different times: the title stays, only the figures move.

display.set({"Furnace room", "", "Coal left"})
display.line(2, "running")
display.line(4, 512)   -- line 4 did not exist yet: it is added

When n is beyond the last line, the lines in between are added, empty. A number below 1 or above 16 is ignored, with no error. n must be a whole number. Leaving out the text writes the word nil: to blank a line, write display.line(n, "").

A stock counter on nixie tubes. A row of three Nixie Tubes shows 6 characters: enough for the iron of the vault on the left. Nixie tubes show the first line only, so the count goes on line 1:

local vault = peripheral.wrap("left")
while true do
  display.line(1, vault.count("minecraft:iron_ingot"))
  sleep(2)
end

See inventory.count() for the vault, and Stock alarm and display board for a complete stock alarm.

See also display.set() display.clear()

Removes every line: the computer offers nothing to its Display Links any more.

At the next reading, a Display Board and Nixie Tubes go blank. A sign and a lectern only blank the first line (or page) the link writes to, and keep the others: to wipe a whole sign, send it empty lines instead.

display.clear()                    -- a board goes blank
display.set({"", "", "", ""})      -- a sign goes blank too

A clock on a sign. The time of day on a sign in the town square, refreshed every few seconds (the built-in clock program does the same with a monitor):

while true do
  local t = (os.day_time() + 6000) % 24000
  local text = string.format("%02d:%02d", t // 1000, t % 1000 * 60 // 1000)
  display.set({"", "Town hall", text, ""})
  sleep(5)
end

A Minecraft hour lasts 50 seconds, so a refresh every 5 seconds keeps the minutes close enough for a town clock.

See also display.set()