dancingLines v2 (computercraft lua)

--[[

dancinglines v2
code by GopherAtl.
Do anything you want with this code except claim credit for it.
If you distribute a program that uses it, please link users to the
official thread on the cc forums here:
http://www.computercraft.info/forums2/index.php?/topic/4006-logo-interpreter/
If you distribute a modified version with fixes or enhancements, please link to
it in the official thread as well.

--]]



--Bresenham's line algo, adapted to lua by me
function line(device,x1,y1,x2,y2,ch)
  local steep = math.abs(y2-y1)>math.abs(x2-x1)
  local setPos
  if steep then
    y1,x1=x1,y1
    y2,x2=x2,y2
    setPos=function(y,x) device.setCursorPos(x,y) end
  else
    setPos=function(x,y) device.setCursorPos(x,y) end
  end
  if x1>x2 then
    x1,x2=x2,x1
    y1,y2=y2,y1
  end
  local dx=x2-x1
  local dy=math.abs(y2-y1)
  local err=dx/2
  local ys= y1<y2 and 1 or -1
  local y=y1

  for x=x1,x2 do
    setPos(x,y)
    device.write(ch)
    err=err-dy
    if err<0 then
      y=y+ys
      err=err+dx
    end
  end
end


local numLines=2
local tailLen=5
local drawEvery=1
local speed=20

local x1, x2, y1, y2
local termW, termH=term.getSize()
local lines={}

local args={...}
if #args>0 and tonumber(args[1]) then
  numLines=tonumber(args[1])
  if numLines<1 then numLines=1 end
  if numLines>10 then numLines=5 end
  if #args>1 and tonumber(args[1]) then
    speed=tonumber(args[2])
    if speed>100 then speed=100 end
    if speed<.1 then speed=.1 end
  end
end

function initLines()

  for i=1,numLines do
    lines[i]= { {
        x1=math.random()*termW,
        x2=math.random()*termW,
        y1=math.random()*termH,
        y2=math.random()*termH,
      },
      x1v=math.random()/1+1,
      x2v=math.random()/1+1,
      y1v=math.random()/1+1,
      y2v=math.random()/1+1,

      }
   end
end

initLines()

local chars={{"O","o","o",".","."},{"X","x","x",",",","}}


function dancingLines()
  while true do
    term.clear()
    for i=#lines[1],1,-2 do
      for j=1,#lines do
        logo.line(term, lines[j][i].x1,lines[j][i].y1,lines[j][i].x2,lines[j][i].y2,chars[j][(i-i%drawEvery)/drawEvery])
      end
    end
    for j=1,#lines,1 do
      if #lines[j]==tailLen then
        table.remove(lines[j],#lines[j])
      end
      newline={
              x1=lines[j][1].x1+lines[j].x1v,
              y1=lines[j][1].y1+lines[j].y1v,
              x2=lines[j][1].x2+lines[j].x2v,
              y2=lines[j][1].y2+lines[j].y2v,
        }
      if newline.x1<1 then
        newline.x1=-newline.x1
        lines[j].x1v=-lines[j].x1v
      elseif newline.x1>termW then
        newline.x1=termW*2-newline.x1
        lines[j].x1v=-lines[j].x1v
      end
      if newline.x2<1 then
        newline.x2=-newline.x2
        lines[j].x2v=-lines[j].x2v
      elseif newline.x2>termW then
        newline.x2=termW*2-newline.x2
        lines[j].x2v=-lines[j].x2v
      end

      if newline.y1<1 then
        newline.y1=-newline.y1
        lines[j].y1v=-lines[j].y1v
      elseif newline.y1>termH then
        newline.y1=termH*2-newline.y1
        lines[j].y1v=-lines[j].y1v
      end
      if newline.y2<1 then
        newline.y2=-newline.y2
        lines[j].y2v=-lines[j].y2v
      elseif newline.y2>termH then
        newline.y2=termH*2-newline.y2
        lines[j].y2v=-lines[j].y2v
      end

      table.insert(lines[j], 1, newline)

      local myTimer=os.startTimer(1/speed)
      while true do
        evt,p1=os.pullEvent()
        if evt=="timer" and p1==myTimer then
          break
        end
        if evt=="char" and p1~=1 then
          if p1=='r' then
            initLines()
          else
            return
          end
        end
      end

    end

  end
end

dancingLines()
term.clear()
term.setCursorPos(1,1)