CC - Matrix Screensaver

--(c) 2013 Felix Maxwell
--License: CC BY-SA 3.0
local fps = 8 --Determines how long the system will wait between each update
local maxLifetime = 40 --Max lifetime of each char
local minLifetime = 8 --Min lifetime of each char
local maxSourcesPerTick = 5 --Maximum number of sources created each tick
local sourceWeight = 0 --Affects the chance that no sources will be generated
local greenWeight = 8 --Threshhold out of 10 that determines when characters will switch from lime to green
local grayWeight = 2 --Same as about, but from green to gray
function getMonitors()
local monitors = {}
if checkMonitorSide( "top" ) then table.insert( monitors, "top" ) end
if checkMonitorSide( "bottom" ) then table.insert( monitors, "bottom" ) end
if checkMonitorSide( "left" ) then table.insert( monitors, "left" ) end
if checkMonitorSide( "right" ) then table.insert( monitors, "right" ) end
if checkMonitorSide( "front" ) then table.insert( monitors, "front" ) end
if checkMonitorSide( "back" ) then table.insert( monitors, "back" ) end
return monitors
end
function checkMonitorSide( side )
if peripheral.isPresent( side ) then
  if peripheral.getType(side) == "monitor" then
   return true
  end
end
return false
end
function printMonitorStats( side )
local x, y = peripheral.call(side, "getSize")
local color = "No"
if peripheral.call(side, "isColor") then
  color = "Yes"
end
print("Side:"..side.." Size:("..x..", "..y..") Color?"..color)
end
function askMonitor()
local monitors = getMonitors()
if #monitors == 0 then
  print("No monitors found, add more!")
  return nill
elseif #monitors == 1 then
  return monitors[1]
else
  while true do
   print("Multiple monitors found, please pick one.")
   for i,v in ipairs(monitors) do
        write("["..(i).."] ")
        printMonitorStats( v )
   end
   write("Selection: ")
   local sel = tonumber(io.read())
   if sel < 1 or sel > #monitors then
        print("")
        print("Invalid number.")
   else
        return monitors[sel]
   end
  end
end
end
function printCharAt( monitor, x, y, char )
monitor.setCursorPos( x, y )
monitor.write( char )
end
function printGrid( monitor, grid, color )
for i=1,#grid do
  for o=1,#grid[i] do
   if color then monitor.setTextColor( grid[i][o]["color"] ) end
   printCharAt( monitor, i, o, grid[i][o]["char"] )
  end
end
end
function colorLifetime( life, originalLifetime )
local lifetimePart = originalLifetime/10
if life < grayWeight*lifetimePart then
  return colors.gray
elseif life < greenWeight*lifetimePart then
  return colors.green
else
  return colors.lime
end
end
function getRandomChar()
local randTable = {"1","2","3","4","5","6","7","8","9","0","!","@","#","$","%","^","&","*","(",")","_","-","+","=","~","`",",","<",">",".","/","?",":","{","}","[","]","\\","\"","\'"}
return randTable[math.random(1, #randTable)]
end
function tick( screen )
--update lifetimes
for x=1,#screen do
  for y=1,#screen[x] do
   screen[x][y]["curLife"] = screen[x][y]["curLife"] - 1
  end
end
--make the sources 'fall' and delete timed out chars
for x=1,#screen do
  for y=1,#screen[x] do
   if screen[x][y]["type"] == "source" and screen[x][y]["curLife"] == 0 then
        screen[x][y]["type"] = "char"
        screen[x][y]["lifetime"] = math.random(minLifetime, maxLifetime)
        screen[x][y]["curLife"] = screen[x][y]["lifetime"]
        screen[x][y]["color"] = colors.lime

        if y < #screen[x] then
         screen[x][y+1]["char"] = getRandomChar()
         screen[x][y+1]["lifetime"] = 1
         screen[x][y+1]["curLife"] = 1
         screen[x][y+1]["type"] = "source"
         screen[x][y+1]["color"] = colors.white
        end
   elseif screen[x][y]["curLife"] < 0 then
        screen[x][y]["char"] = " "
        screen[x][y]["lifetime"] = 0
        screen[x][y]["curLife"] = 0
        screen[x][y]["type"] = "blank"
        screen[x][y]["color"] = colors.black
   elseif screen[x][y]["type"] == "char" then
        screen[x][y]["color"] = colorLifetime( screen[x][y]["curLife"], screen[x][y]["lifetime"] )
   end
  end
end

--create new character sources
local newSources = math.random( 0-sourceWeight, maxSourcesPerTick )
for i=1,newSources do
  local col = math.random(1, #screen)
  screen[col][1]["char"] = getRandomChar()
  screen[col][1]["lifetime"] = 1
  screen[col][1]["curLife"] = 1
  screen[col][1]["type"] = "source"
  screen[col][1]["color"] = colors.white
end

return screen
end
function setup( w, h )
local retTab = {}
for x=1,w do
  retTab[x] = {}
  for y=1,h do
   retTab[x][y] = {}
   retTab[x][y]["char"] = " "
   retTab[x][y]["lifetime"] = 0
   retTab[x][y]["curLife"] = 0
   retTab[x][y]["type"] = "blank"
   retTab[x][y]["color"] = colors.black
  end
end
return retTab
end
function run()
local monitor = peripheral.wrap( askMonitor() )
local color = monitor.isColor()
local w, h = monitor.getSize()
local screen = setup( w, h )
while true do
  screen = tick( screen )
  printGrid( monitor, screen, color )
  os.sleep(1/fps)
end
end
run()