-- constants
WIDTH = 128
HEIGHT = 128
FOV = math.pi / 2 -- field of view
DEPTH = 16 -- number of depth levels

-- map data
map = {
  {1,1,1,1,1,1,1,1,1,1},
  {1,0,0,0,0,0,0,0,0,1},
  {1,0,0,0,0,0,0,0,0,1},
  {1,0,0,0,0,0,0,0,0,1},
  {1,0,0,0,0,0,0,0,0,1},
  {1,0,0,0,0,0,0,0,0,1},
  {1,0,0,0,0,0,0,0,0,1},
  {1,0,0,0,0,0,0,0,0,1},
  {1,0,0,0,0,0,0,0,0,1},
  {1,1,1,1,1,1,1,1,1,1}
}

-- player position and direction
pos = {x=5, y=5}
dir = {x=1, y=0}

-- function to calculate the distance to the wall
function calc_dist(x, y, dir_x, dir_y)
  -- calculate the step and initial side distance
  local step_x, step_y
  local side_dist_x, side_dist_y
  if dir_x < 0 then
    step_x = -1
    side_dist_x = (pos.x - x) * 2
  else
    step_x = 1
    side_dist_x = (x + 1 - pos.x) * 2
  end
  if dir_y < 0 then
    step_y = -1
    side_dist_y = (pos.y - y) * 2
  else
    step_y = 1
    side_dist_y = (y + 1 - pos.y) * 2
  end

  -- perform DDA
  local hit = 0
  local side = 0
  while hit == 0 do
    if side_dist_x < side_dist_y then
      side_dist_x = side_dist_x + 2
      x = x + step_x
      side = 0
    else
      side_dist_y = side_dist_y + 2
      y = y + step_y
      side = 1
    end
    if map[y][x] > 0 then
      hit = 1
    end
  end

  -- calculate the distance to the wall
  local dist
  if side == 0 then
    dist = math.abs((x - pos.x + (1 - step_x) / 2) / dir_x)
  else
    dist = math.abs((y - pos.y + (1 - step_y) / 2) / dir_y)
  end
  return dist
end

function _draw()
  -- clear the screen
  cls()

-- loop through each column of the screen
for x = 0, WIDTH - 1 do
  -- calculate the ray direction
  local camera_x = 2 * x / WIDTH - 1 -- x-coordinate in camera space
  local ray_dir_x = dir.x + dir.y * camera_x
  local ray_dir_y = dir.y - dir.x * camera_x

  -- calculate the distance to the wall
  local dist = calc_dist(math.floor(pos.x), math.floor(pos.y), ray_dir_x, ray_dir_y)

  -- calculate the size of the wall slice
  local wall_slice_height = math.floor(HEIGHT / dist)

  -- calculate the top and bottom of the wall slice
  local wall_slice_top = math.floor((HEIGHT - wall_slice_height) / 2)
  local wall_slice_bottom = wall_slice_top + wall_slice_height - 1

  -- draw the wall slice
  for y = 0, HEIGHT - 1 do
    if y < wall_slice_top then
      pset(x, y, 7) -- ceiling
    elseif y > wall_slice_bottom then
      pset(x, y, 8) -- floor
    else
      pset(x, y, 6) -- wall
    end
  end
end

//calculate step and initial sideDist

//perform DDA