Example code for part 3 of my Cameras in Love2D tutorial series.

camera.lua

camera = {}
camera._x = 0
camera._y = 0
camera.scaleX = 1
camera.scaleY = 1
camera.rotation = 0

function camera:set()
  love.graphics.push()
  love.graphics.rotate(-self.rotation)
  love.graphics.scale(1 / self.scaleX, 1 / self.scaleY)
  love.graphics.translate(-self._x, -self._y)
end

function camera:unset()
  love.graphics.pop()
end

function camera:move(dx, dy)
  self._x = self._x + (dx or 0)
  self._y = self._y + (dy or 0)
end

function camera:rotate(dr)
  self.rotation = self.rotation + dr
end

function camera:scale(sx, sy)
  sx = sx or 1
  self.scaleX = self.scaleX * sx
  self.scaleY = self.scaleY * (sy or sx)
end

function camera:setX(value)
  if self._bounds then
    self._x = math.clamp(value, self._bounds.x1, self._bounds.x2)
  else
    self._x = value
  end
end

function camera:setY(value)
  if self._bounds then
    self._y = math.clamp(value, self._bounds.y1, self._bounds.y2)
  else
    self._y = value
  end
end

function camera:setPosition(x, y)
  if x then self:setX(x) end
  if y then self:setY(y) end
end

function camera:setScale(sx, sy)
  self.scaleX = sx or self.scaleX
  self.scaleY = sy or self.scaleY
end

function camera:getBounds()
  return unpack(self._bounds)
end

function camera:setBounds(x1, y1, x2, y2)
  self._bounds = { x1 = x1, y1 = y1, x2 = x2, y2 = y2 }
end

main.lua

require('camera')

function love.load()
  width = love.graphics.getWidth()
  height = love.graphics.getHeight()
  camera:setBounds(0, 0, width, height)
  
  player = {
    x = width / 2,
    y = height / 2,
    width = 50,
    height = 50,
    speed = 300,
    color = { 150, 150, 150 }
  }
  
  box = {
    x = 0,
    y = 0,
    width = width * 2,
    height = height * 2,
    color = { 255, 20, 20 }
  }
  
  stuff = {}
  
  for i = 1, 10 do
    table.insert(stuff, {
      x = math.random(100, width * 2 - 100),
      y = math.random(100, height * 2 - 100),
      width = math.random(100, 300),
      height = math.random(100, 300),
      color = { 255, 255, 255 }
    })
  end
end

function love.update(dt)
  if love.keyboard.isDown('left') then
    player.x = player.x - player.speed * dt
  elseif love.keyboard.isDown('right') then
    player.x = player.x + player.speed * dt
  elseif love.keyboard.isDown('up') then
    player.y = player.y - player.speed * dt
  elseif love.keyboard.isDown('down') then
    player.y = player.y + player.speed * dt
  end
  
  camera:setPosition(player.x - width / 2, player.y - height / 2)
end

function love.draw()
  camera:set()
  
  -- box
  love.graphics.setColor(box.color)
  love.graphics.rectangle('line', box.x, box.y, box.width, box.height)
  
  -- stuff
  for _, v in pairs(stuff) do
    love.graphics.setColor(v.color)
    love.graphics.rectangle('fill', v.x, v.y, v.width, v.height)
  end
  
  -- player
  love.graphics.setColor(player.color)
  love.graphics.rectangle('fill', player.x, player.y, player.width, player.height)
  
  camera:unset()
end

function math.clamp(x, min, max)
  return x < min and min or (x > max and max or x)
end