-- load image to recognize

loadSnippet("#100")()

minWidth=10

minHeight=5

bgcolor=0

function isSet(pixel)

  return pixel ~= nil and pixel ~= bgcolor

end

function on(x, y)

  return x >= 0 and y >= 0 and x < width and y < height

    and isSet(pixels[y*width+x])

end

function check(x, y, pivot)

  if pivot == 2 then return true end

  local is = on(x, y) == true

  local should = pivot == 1

  --print("check", x, y, is, should)

  return is == should

end

function detectNode(x, y, a, b, c, d, e, f, g, h, i)

  --print("xy", x, y, "abcdef", a, b, c, d, e, f)

  return check(x-1, y-1, a)

    and check(x, y-1, b)

    and check(x+1, y-1, c)

    and check(x-1, y, d)

    and check(x, y, e)

    and check(x+1, y, f)

    and check(x-1, y+1, g)

    and check(x, y+1, h)

    and check(x+1, y+1, i)

end

function detect(x1, y1)

  if not detectNode(x1, y1, 0, 0, 0, 0, 1, 1, 0, 1, 0) then return end

  --print("Corner found! ", x1, y1)

  local x=x1+1

  while on(x, y1) and not on(x, y1-1) and not on(x, y1+1)

    and x < width do x=x+1 end

  if x<x1+minWidth then return end

  local y=y1+1

  while on(x, y) and not on(x-1, y) and not on(x+1, y1)

    and y < height do y=y+1 end

  if y<y1+minHeight then return end

  -- TODO: check bottom and left

  return {x1, y1, x-x1+1, y-y1+1}

end

function clearRectangle(p)

  local x1, y1, w, h = unpack(p)

  for x=0, w-1 do

    pixels[(x1+x)+y1*width] = bgcolor

    pixels[(x1+x)+(y1+h-1)*width] = bgcolor

  end

  for y=1, h-2 do

    pixels[x1+(y1+y)*width] = bgcolor

    pixels[x1+w-1+(y1+y)*width] = bgcolor

  end

end

positions = {}

for y1=0,height-1 do

  for x1=0,width-1 do

    local p = detect(x1,y1)

    if p then

      print("Rectangle found: "..tostring(p[1]).." "..tostring(p[2]).." "..tostring(p[3]).." "..tostring(p[4]))

      clearRectangle(p)

      table.insert(positions, p)

    end

  end

end