--rubb.lua
--elastic bond simulator
--code by Siapran
--19.02.2013

--you may modify the following values to suit your needs:
local n=2 --number of modules (>0)
local g=1/10 --gravity
local r=1/32 --elasticity
local f=99/100 --friction
--end of user values

local line=graydraw.line
local rect=graydraw.rect
local wait=misc.wait

local x={} --coordinates
local y={}
local xm={} --momentum
local ym={}

n=n+1

for a=1,n,1 do --initialise modules
 x[a]=64
 y[a]=32
 xm[a]=0
 ym[a]=0
end

graydraw.setcolor(true) --initiate grayscale mode

for a=1,4,1 do --adjust contrast
 misc.contrast(1)
end


repeat --main loop

 clear nil --clear buffer
 
 if key(37) then x[1]=x[1]-1 end --move holding point
 if key(40) then x[1]=x[1]+1 end
 if key(38) then y[1]=y[1]-1 end
 if key(39) then y[1]=y[1]+1 end
 if x[1]<1 then x[1]=1 end --clipping
 if x[1]>128 then x[1]=128 end
 if y[1]<1 then y[1]=1 end
 if y[1]>64 then y[1]=64 end
 
 for a=2,n,1 do --compute elastic tention in one way
  xm[a]=xm[a]+(x[a-1]-x[a])*r
  ym[a]=ym[a]+(y[a-1]-x[a])*r
 end
 
 if n<2 then --compute elastic tention in the other way
  for a=2,n-1,1 do
   xm[a]=xm[a]+(x[a+1]-x[a])*r
   ym[a]=ym[a]+(y[a+1]-x[a])*r
  end
 end
 
 for a=2,n,1 do --apply gravity and friction, then computer changes
  ym[a]=ym[a]+g
  xm[a]=xm[a]*f
  ym[a]=ym[a]*f
  x[a]=x[a]+xm[a]
  y[a]=y[a]+ym[a]
  
  line(x[a-1],y[a-1],x[a],y[a],4) --draw elastic bond
  rect(x[a]-3,y[a]-3,x[a]+3,y[a]+3,4,0) --draw module box
 end
 
 line(x[1]-3,y[1],x[1]+3,y[1],4)
 line(x[1],y[1]-3,x[1],y[1]+3,4)
 
 refresh

until key(36) --wait for key [EXIT]

while key(36) do wait(1) end