LÖVE

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-- camera.lua
-- viewport and boundaries are expressed as left, top, width and height
local viewport = {
  l = 0,
  t = 0,
  w = love.graphics.getWidth(),
  h = love.graphics.getHeight()
}

local boundary = {
  l = 0,
  t = 0,
  w = viewport.width,
  h = viewport.height
}

local function clampNumber(v, min, max)
  if max < min then return 0 end -- this happens when viewport is bigger than boundary
  return v < min and min or (v > max and max or v)
end

local function clampCamera()
  viewport.l = clampNumber(viewport.l, boundary.l, boundary.l + boundary.w - viewport.w)
  viewport.t = clampNumber(viewport.t, boundary.t, boundary.t + boundary.h - viewport.h)
end

local function setViewport(l, t, w, h)
  viewport.l, viewport.t, viewport.w, viewport.h = l, t, w or viewport.w, h or viewport.h
  clampCamera()
end

local function setBoundary(l, t, w, h)
  boundary.l, boundary.t, boundary.w, boundary.h = l, t, w, h
  clampCamera()
end

local function lookAt(x,y)
  setViewport(math.floor(x - viewport.w / 2), math.floor(y - viewport.h / 2))
end

local function draw(f)
  love.graphics.push()
  love.graphics.translate(-viewport.l, -viewport.t)
  f()
  love.graphics.pop()
end

local function getViewport()
  return viewport.l, viewport.t, viewport.w, viewport.h
end

return {
  setViewport = setViewport,
  setBoundary = setBoundary,
  getViewport = getViewport,
  lookAt      = lookAt,
  draw        = draw
}

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local camera = require 'camera'

local worldWidth, worldHeight = 3000, 2000

function love.load()
  -- The camera is bound to a rectangle with corners in 0,0 and dimensions 3000x2000
  camera.setBoundary(0,0, worldWidth, worldHeight)
end

function love.update(dt)
...
  -- center the camera on coordinates 200, 300
  camera.lookAt(200, 300)
...
end

function love.draw()
  love.graphics.print(100, 100, "This will be drawn without the camera")
  camera.draw(function()
    love.graphics.print(100, 100, "This will be drawn with the camera")
  end)
end

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camera.setViewport(0,0, love.graphics.getWidth(), love.graphics.getHeight())
-- you will probably want to "look at what you were looking" after updating the viewport; for example:
camera.lookAt(player.x, player.y)

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function Play:draw()
  camera.draw(function()
    map:draw(camera.getViewport())
  end)
end

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function Map:draw(wl, wt, ww, wh) -- left, top, witdh, height of the visible rectangle in the world
  local l, t = self:toMap(wl, wt) -- left, top tiles of the rectangle
  local r, b = self:toMap(wl + ww, wt + wh) -- right, bottom tiles of the rectangle

  -- draw only the tiles between left, top and right, bottom
  for x = l, r do
    for y = t, b do
      self.tiles[x][y]:draw()
    end
  end
end