Autoshooter game in Love2d

Question

I ported a little game I originally made in Macroquad to Love2d. But I have also added additional features, like additional animations and screen shake. I have used HUMP for various utilities. shack for screen shake. HC for collision and tiny-ecs for an entity component system. You are a circle with a gun that shoots automatically at other enemies. The enemies follow you around and your goal is to dodge them. The game looks like this:

Game

Here is the code:

local Gamestate = require("hump.gamestate")
local Vector = require("hump.vector")
local Timer = require("hump.timer")
local Camera = require("hump.camera")
local HC = require("HC")
local tiny = require("tiny")
local screen = require("shack")
-- Different scenes for the game.
local game = {}
local gameover = {}
-- Processing logic here for enemies, bullets, and tank.
local processEnemies = tiny.processingSystem()
processEnemies.filter = tiny.filter("radius&pos&angle&speed&shape&!gun_length")
function processEnemies:onAdd(e)
 Timer.tween(0.5, e, {angle=2*math.pi}, 'linear', function() 
 e.speed = 50 
 end) 
end
function processEnemies:process(e, dt)
 love.graphics.setLineWidth(5)
 love.graphics.arc( "line", "open", 
 e.pos.x, e.pos.y,
 e.radius, 0, e.angle)
 e.pos = e.pos + (tank.pos - e.pos):normalizeInplace() * dt * e.speed
 e.shape:moveTo(e.pos.x, e.pos.y)
end
local processBullet = tiny.processingSystem()
processBullet.filter = tiny.filter("pos&shape&speed&bullet")
function processBullet:onAdd(e)
 e.pos = tank.pos
 e.shape:moveTo(e.pos.x, e.pos.y)
 e.dir = tank.gun_vec:normalized()
end
function processBullet:process(e, dt)
 love.graphics.setLineWidth(5)
 love.graphics.circle("fill", e.pos.x, e.pos.y, 5)
 e.pos = e.pos + e.dir * dt * e.speed
 e.shape:moveTo(e.pos.x, e.pos.y)
 for shape, delta in pairs(HC.collisions(e.shape)) do
 if enemies[shape] ~= nil then
 world:remove(enemies[shape])
 table.remove(enemies[shape])
 end
 end
end
local processTank = tiny.processingSystem()
processTank.filter = tiny.filter("radius&pos&angle&gun_length&gun_vec")
function processTank:onAdd(e)
 local drawGun = function()
 Timer.tween(0.5, e, {gun_length=20}, 'linear',
 function()
 e.speed = 100
 end)
 end
 Timer.tween(0.5, e, {angle=2*math.pi}, 'linear', drawGun)
end
function tankKeypress(e, dt)
 -- Handle key presses.
 local delta = Vector(0, 0)
 if love.keyboard.isDown('left') then
 delta.x = -1
 elseif love.keyboard.isDown('right') then
 delta.x = 1
 end
 if love.keyboard.isDown('up') then
 delta.y = -1
 elseif love.keyboard.isDown('down') then
 delta.y = 1
 end
 delta:normalizeInplace()
 e.pos = e.pos + delta * dt * e.speed 
end
function tankCollision(e, dt)
 -- Update collision information.
 e.shape:moveTo(e.pos.x, e.pos.y)
 e.shot_radius:moveTo(e.pos.x, e.pos.y)
 local gun_angle = 0
 for shape, delta in pairs(HC.collisions(e.shot_radius)) do
 if enemies[shape] ~= nil then
 local sx, sy = shape:center()
 gun_angle = math.atan2(sy - e.pos.y, sx - e.pos.x)
 break
 end
 end
 for shape, delta in pairs(HC.collisions(e.shape)) do
 if enemies[shape] ~= nil then
 screen:setShake(20)
 local new_health = healthbar.health - 0.5
 Timer.tween(0.5, healthbar, {
 health=math.max(new_health, 0)
 }, "linear")
 if healthbar.health <= 0 then
 Gamestate.switch(gameover)
 end
 break
 end
 end
 return gun_angle
end
function processTank:process(e, dt)
 tankKeypress(e, dt)
 local gun_angle = tankCollision(e, dt)
 -- Draw tank.
 e.gun_vec = Vector(e.gun_length, 0):rotated(gun_angle)
 love.graphics.setLineWidth(5)
 love.graphics.arc( "line", "open", 
 e.pos.x, e.pos.y,
 e.radius, 0, e.angle)
 love.graphics.line(e.pos.x, e.pos.y,
 e.pos.x + e.gun_vec.x,
 e.pos.y + e.gun_vec.y)
end
function game:draw()
 -- Draw healthbar.
 love.graphics.line(10, 10,
 10 + healthbar.health, 10)
 camera:attach()
 screen:apply()
 world:update(love.timer.getDelta())
 camera:detach()
end
function game:update(dt)
 -- Handle timers and screen shake libraries.
 Timer.update(dt)
 screen:update(dt)
 -- Handle camera.
 local CAMERA_SLOW_FACTOR = 100
 local dx, dy = tank.pos.x - camera.x, tank.pos.y - camera.y
 camera:move(dx / CAMERA_SLOW_FACTOR, dy / CAMERA_SLOW_FACTOR) 
end
function gameover:draw()
 love.graphics.print('The End', 
 love.graphics.getWidth() / 2, 
 love.graphics.getHeight() / 2)
end
function game:init()
 -- For checking if an enemy is in range of a player.
 tank = {
 pos=Vector(300, 400), gun_vec=Vector(1,0),
 gun_length=0, speed=0, angle=0, radius=20,
 shape=HC.circle(300, 400, 20),
 shot_radius=HC.circle(300, 400, 50)
 }
 enemies = {}
 healthbar = {health = 60}
 world = tiny.world(processTank, processEnemies, processBullet, tank)
 camera = Camera(tank.pos.x, tank.pos.y)
 -- Spawn enemies.
 Timer.every(1, function()
 local angle = love.math.random()
 local x = tank.pos.x + 300 * math.cos(2 * math.pi * angle)
 local y = tank.pos.y + 300 * math.sin(2 * math.pi * angle)
 local shape = HC.circle(x, y, 20)
 local enemy = {
 pos=Vector(x, y), speed=0, angle=0, radius=20,
 shape=shape
 }
 tiny.add(world, enemy)
 enemies[shape] = enemy
 end)
 -- Spawn bullets.
 Timer.every(5, function()
 tiny.add(world, {
 speed=100, 
 shape=HC.point(0,0),
 pos=Vector(0, 0),
 bullet = {}
 })
 end)
end
function love.load()
 Gamestate.registerEvents()
 Gamestate.switch(game)
end