bgColor = -1 -- white
fontW, fontH = 16, 16
displayCols, displayRows = 40, 10
displayW, displayH = fontW*displayCols, fontH*displayRows
width, height = displayW, displayH
cursorBlinkRate = 500
--eventRate = 50
eventRate = 20 -- high speed!
eventsPerCursorBlink = cursorBlinkRate/eventRate
needsRepaint = false
repaintTriggeringVars = {"curX", "curY", "cursorVisible", "scrollX", "scrollY"}
fatCursor = true

autoScroll = loadSnippet("#192")

-- volatile data
if not inited then
  scrollX, scrollY = 0, 0
  curX, curY = 0, 0
  if lines == nil then lines = {"hello", "world"} end
  needsRepaint = true
  inited = true
end

local min, max = math.min, math.max

get("#109") -- copyRect

fontRendererEnv = newCleanEnv()
--fontRenderer = get("#178", fontRendererEnv)
fontRenderer = get("#186", fontRendererEnv)

grab("#175") -- tableToString

function renderText(x, y, s)
  --print("renderText", x, y, s)
  fontRendererEnv.render(s)
  --print("fontWidth="..tostring(fontRendererEnv.fontWidth))
  copyRect(fontRendererEnv, _G, 0, 0, fontRendererEnv.width, fontRendererEnv.height, x, y)
  --[[for y=0, 1 do
    for x=0, 15 do
      print(fontRendererEnv.pixels[x+y*fontRendererEnv.width+1])
    end
  end]]
end

-- "hook" is an identifier for the place to extend.
-- example: "processEvents" for extending the processEvents
-- function.
function extensions(hook)
  -- put your extensions here :)
end

function setPixel(x, y, col)
  if x >= 0 and y >= 0 and x < displayW and y < displayH then
    pixels[x+y*width+1] = col
  end
end

function invertPixel(x, y)
  if x >= 0 and y >= 0 and x < displayW and y < displayH then
    local ofs = x+y*width+1
    pixels[ofs] = pixels[ofs] and -1-pixels[ofs] or -1
  end
end

function stepCursor()
  if lastCurX ~= curX or lastCurY ~= curY then
    cursorCount = -1
  end
  lastCurX = curX
  lastCurY = curY
  cursorCount = (cursorCount+1) % (eventsPerCursorBlink*2)
  cursorVisible = cursorCount < eventsPerCursorBlink
end

function renderCursor()
  if cursorVisible then
    for x=0, fatCursor and fontW-1 or 0 do
      for y=0, fontH-1 do
        invertPixel((curX-scrollX)*fontW+x, (curY-scrollY)*fontH+y)
      end
    end
  end
end

function cursorLeft()
  if curX > 0 then
    curX=curX-1
  elseif curY > 0 then
    curY=curY-1
  end
end

function cursorRight()
  curX=curX+1
end

function cursorUp()
  if curY > 0 then
    curY=curY-1
  end
end

function cursorDown()
  if curY < #lines-1 then
    curY=curY+1
  end
end

function saveVars()
  savedVars = {}
  for _, var in ipairs(repaintTriggeringVars) do
    savedVars[var] = _G[var]
  end
end

function compareVars()
  for _, var in ipairs(repaintTriggeringVars) do
    if savedVars[var] ~= _G[var] then
      needsRepaint = true
      return
    end
  end
end

function moveCursorToSpot(x, y)
  local col = math.floor((x+scrollX)/fontW)
  local row = math.floor((y+scrollY)/fontH)
  row = max(0, min(row, #lines-1))
  col = max(0, col)
  curX, curY = col, row
end

function insertText2(s)
  if s == '' then return end
  local l = lines[curY+1]
  local left, right = l:sub(1, curX), l:sub(curX+1)
  if s == '\n' then
    table.insert(lines, curY+1, left)
    lines[curY+2] = right
    curY = curY+1
    curX = 0
  else
    lines[curY+1] = left..s..right
    curX = curX+#s
    needsRepaint = true
  end
end

function insertText(s)
  local i = s:find("\n", 1, plain)
  if not i then
    insertText2(s)
  else
    insertText2(s:sub(1, i-1))
    insertText2("\n")
    insertText(s:sub(i+1)) -- gotta love recursion!
  end
end

function backspace()
  local l = lines[curY+1]
  if curX > 0 then
    lines[curY+1] = l:sub(1, curX-1)..l:sub(curX+1)
    curX=curX-1
  elseif curY > 0 then
    local p = lines[curY]
    lines[curY] = p..l
    table.remove(lines, curY+1)
    curY=curY-1
    curX=#p
  end
end

function home()
  curX = 0
end

function endPos()
  curX = #lines[curY+1]
end

function processEvents()
  saveVars()
  
  if inputEvents then
    for _, e in ipairs(inputEvents) do
      --print("event:", tableToString(e))
      if e[1] == 'keyPressed' then
        if e.keyCode == 39 then
          cursorRight()
        elseif e.keyCode == 37 then
          cursorLeft()
        elseif e.keyCode == 40 then
          cursorDown()
        elseif e.keyCode == 38 then
          cursorUp()
        elseif e.keyCode == 0x24 then
          home()
        elseif e.keyCode == 0x23 then
          endPos()
        end
    elseif e[1] == 'keyTyped' then
        if e.keyChar == '\8' then
          backspace()
        else
          insertText(e.keyChar)
        end
      elseif e[1] == 'mousePressed' then
        moveCursorToSpot(e.x, e.y)
      end
    end
  end
  extensions('processEvents1')
  
  stepCursor()
  autoScroll()
  extensions('processEvents')
  compareVars()
end

function render()
  if needsRepaint then
    pixels = {}
    for i = 1, width*height do pixels[i] = bgColor end

    for l = 1, min(#lines-scrollY, displayRows) do
      renderText(0, (l-1)*fontH, lines[l+scrollY]:sub(scrollX+1, scrollX+1+displayCols))
    end
    
    renderCursor()
    needsRepaint = false
  end
end

function step()
  pixels = nil
  processEvents()
  render()
  if exit then
    animateAgainIn = nil
  else
    animateAgainIn = {eventRate, step}
  end
end

step()

Began life as a copy of #172