text running

-- Writes text centered, x- and y-axis position can be offset, and the line to be written can be cleared beforehand.
local function writeCentered( _sText, _nOffsetX, _nOffsetY, _nColor, _bClearLine )
    local maxX, maxY = term.getSize()

    if _nOffsetX == null then _nOffsetX = 0 end
    local centeredX = (maxX / 2) - (string.len( _sText ) / 2) + _nOffsetX

    if _nOffsetY == null then _nOffsetY = 0 end
    local centeredY = (maxY / 2) + _nOffsetY

    term.setCursorPos( centeredX, centeredY )
    if _bClearLine then term.clearLine() end
    if _nColor and term.isColor() then term.setTextColor( _nColor ) end
    write( _sText )
    if _nColor and term.isColor() then term.setTextColor( colors.white ) end
end

-- Scrolls text form left to right.
--  _text  = Text to scroll
--  _dleay = Scroll-Delay in seconds (optional; defaults to 0.1)
--  _yPos  = Y-Position to display marquee (optional; defaults to center)
local function marquee( _text, _delay, _yPos )
    local nScrollTime = _delay or 0.1 -- Scroll-Time in seconds
    local counter = 0
    local sMarquee = _text
    local xMax, yMax = term.getSize()
    yPos = _yPos or (yMax / 2)

    local scrollTimer = os.startTimer( nScrollTime )
    while true do
        local sEvent, sPar = os.pullEvent()

        if sEvent == "char" and string.lower(sPar) == "q" then
            print()
            break
        end

        if sEvent == "timer" and sPar == scrollTimer then
            -- If the marquee has vanished completely into the right side, reset everything.
            if counter > (xMax + string.len(_text)) then
                counter = string.len(_text) + 1
                sMarquee = _text
            end

            -- (Re-)Set the cursor to the beginning of the line.
            term.setCursorPos(1, yPos)

            -- Pad left side with whitespaces if _text has been completely scrolled out from the left side.
            if counter >= string.len(_text) then
                sMarquee = " "..sMarquee
            end

            -- Wrap marquee text around if it reaches the end of the screen.
            if string.len(sMarquee) > xMax then
                sMarquee = string.sub(sMarquee, -1) .. string.sub(sMarquee, 2, string.len(sMarquee) - 1)
            end

            -- Write the marquee.
            if counter ~= 0 then
                write( string.sub(sMarquee, 0 - counter) )
            end

            -- Reset counter.
            counter = counter + 1
            scrollTimer = os.startTimer( nScrollTime )
        end
    end
end

term.clear()
marquee( "Press Q to quit." )

-- Scrolls text form left-to-right (default) or right-to-left
--   _sText    = Text to scroll                                  (mandatory)
--   _bReverse = true for right-to-left, false for left-to-right (optional; defaults to left-to-right)
--   _nDelay   = Scroll-Delay in seconds                         (optional; defaults to 0.1)
--   _yPos     = Y-Position to display marquee                   (optional; defaults to center)
local function marquee( _sText, _bReverse, _nDelay, _yPos )
  if not _sText then
    error("No text found")
  end

  -- Initialize Variables
  local nScrollTime  = _nDelay or 0.1 -- Scroll-Time in seconds
  local xMax, yMax   = term.getSize()
  local xPos         = 1
  local step         = _bReverse and -1 or 1
  local marquee_main = _sText
  local marquee_rest = ""
                yPos = _yPos or (yMax / 2)

  -- Start timer
  local scrollTimer = os.startTimer( nScrollTime )
  -- Start event loop
  while true do
    local sEvent, sPar = os.pullEvent()

    -- Quit on pressing Q
    if sEvent == "char" and string.lower(sPar) == "q" then
        print()
        break

    -- Wrap marquee text around if it reaches the end of the screen.
    elseif sEvent == "timer" and sPar == scrollTimer then

      -- Wrap for right-to-left
      if not _bReverse and (xPos + #marquee_main > xMax) then
        marquee_rest = string.sub(marquee_main, -1) .. marquee_rest
        marquee_main = string.sub(marquee_main, 1, #marquee_main - 1)
        term.setCursorPos(1, yPos)
        term.clearLine()
        write( marquee_rest )
        term.setCursorPos(xPos, yPos)
        write( marquee_main )

      -- Wrap for left-to-right
      elseif _bReverse and (xPos <= 0) then
        marquee_rest = marquee_rest .. string.sub(marquee_main, 1, 1)
        marquee_main = string.sub(marquee_main, 2)
        term.setCursorPos(1, yPos)
        term.clearLine()
        write( marquee_main )
        term.setCursorPos(xMax - #marquee_rest, yPos)
        write( marquee_rest )
        xPos = 1

      -- Continue scrolling, no wrap-around yet.
      else
        term.setCursorPos(xPos, yPos)
        term.clearLine()
        write( marquee_main )
      end

      -- Reset after a full wrap-around occurs.
      if #marquee_rest >= #_sText then
        marquee_rest = ""
        marquee_main = _sText

        if _bReverse then
          -- Reset cursor position for left-to-right
          xPos = xMax - #marquee_main
        else
          -- Reset cursor position for right-to-left
          xPos = 1
        end
      end

      -- Increment/Decrement x-Position
      xPos = xPos + step
      -- Restart timer
      scrollTimer = os.startTimer( nScrollTime )
    end
  end
end

term.clear()
marquee( "Press Q to quit.", true )