Display

The display functions draw text and graphics on the screen of products that have a built-in display.

On products without a display, every display function is simply ignored, so the same script remains safe to run on any device.

Available for OS7.1.0 and later

display.print(string)

Appends a string at the current cursor position. The cursor advances as characters are written, so calling display.print() repeatedly continues the text from where it left off, much like a typewriter.

Arguments

display.clear()

Clears the entire screen.

display.raw(table)

Draws a raw framebuffer directly to the screen.

The table is a byte array in which each element holds a single byte from 0 to 255. The bytes are laid out vertically, following the framebuffer format of the display.

Arguments

Example: Typewriter Text

The following example reveals each message one character at a time, producing a typewriter effect.

local messages = {
  "Hello from obniz",
  "Lua is running on the device.",
  "Bye!",
}

local msg_index = 1
local char_index = 0
local tick = 0
local interval = 120 -- milliseconds per character

os.log(" - Lua PowerOn");
display.clear();

function on_offline_loop()
  loop()
end

function on_online_loop()
  loop()
end

function loop()
  if tick + interval < os.getTick() then
    tick = os.getTick()

    local msg = messages[msg_index]
    if char_index < #msg then
      -- Append the next single character
      char_index = char_index + 1
      display.print(msg:sub(char_index, char_index));
    else
      -- Move on to the next message
      char_index = 0
      msg_index = msg_index + 1
      if msg_index > #messages then
        msg_index = 1
      end
    end
  end
end