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main.lua

local Vector
do
	local V_MT, sqrt, type, unpack, setmetatable = {}, math.sqrt, type, unpack, setmetatable
	V_MT.__index = V_MT

	function V_MT:__add(b)
		return Vector(self.x + b.x, self.y + b.y)
	end
	function V_MT:__sub(b)
		return Vector(self.x - b.x, self.y - b.y)
	end
	function V_MT:__mul(b)
		return Vector(self.x * b, self.y * b)
	end
	function V_MT:__div(b)
		return Vector(self.x / b, self.y / b)
	end
	function V_MT:__tostring()
		return ("{%f, %f}"):format(self.x, self.y)
	end

	function V_MT:length()
		return math.sqrt(self.x * self.x + self.y * self.y)
	end
	function V_MT:length2()
		return self.x * self.x + self.y * self.y
	end
	function V_MT:normalized()
		return self / self:length()
	end

	function Vector(x, y)
		if type(x) == 'table' then
			if x.x then
				x, y = x.x, x.y
			else
				x, y = unpack(x)
			end
		end
		return setmetatable({x = x or 0, y = y or 0}, V_MT)
	end
end


local Particle, ParticleSystem
do
	local PT_PROTO = {}
	PT_PROTO.__index = PT_PROTO
	function PT_PROTO:init(data)
		data = data or {}
		self.birth = love.timer.getMicroTime()
		self.lifetime = data.lifetime
		self.vel = data.vel or Vector(0, 0)
		if self.setup then self:setup(data) end
	end

	function PT_PROTO:think(dt)
		self.pos = self.pos + self.vel * dt
		self.age = love.timer.getMicroTime() - self.birth
		if self.lifetime < self.age then
			if not (self.death and self:death()) then
				self.dead = true
			end
		end
		if self.update then self:update(dt) end
	end

	function Particle(tbl)
		tbl.__index = tbl
		setmetatable(tbl, PT_PROTO)
		return function (system, pos, ...)
			local part = {system, pos = pos}
			setmetatable(part, tbl)
			if part.init then part:init(...) end
			return part
		end
	end
	local PS_MT = {}
	PS_MT.__index = PS_MT
	function PS_MT:create(pos, ...)
		self.particles[#self.particles + 1] = self:pt_create(pos, ...)
	end
	function PS_MT:draw()
		for _, v in ipairs(self.particles) do
			if v and not v.dead then v:draw() end
		end
	end
	function PS_MT:think(dt)
		for _, v in ipairs(self.particles) do
			if v and not v.dead then v:think(dt) end
		end
	end
	function PS_MT:trim()
		-- XXX: skips one particle per particle removed
		for i = 1, #self.particles do
			-- TODO: Break out of loop if self.particles[i] == nil?
			if self.particles[i] and self.particles[i].dead then
				table.remove(self.particles, i)
			end
		end
	end

	function ParticleSystem(new_part)
		local ps = {pt_create = new_part, particles = {}}
		setmetatable(ps, PS_MT)
		return ps
	end
end

Explosion = Particle {
	setup = function (self, data)
		self.elapsed = 0
		self.color = data.color
	end,
	draw = function (self)
		local r, t = (1 - (love.timer.getMicroTime() - self.birth) / self.lifetime),  self.pos - self.vel:normalized() * 0.5
		if r < 0.1 then r = 1 end
		self.color[4] = 255 * r
		love.graphics.setColor(self.color)
		love.graphics.line(self.pos.x, self.pos.y, t.x, t.y)
	end,
	update = function (self, dt)
		if self.age > 0.1 and not self.slowdown then
			self.vel = self.vel / 200
			self.slowdown = true
		end
	end
}

Rocket = Particle {
	setup = function (self, data)
		self.emitter = data.emitter
		self.sound = data.sound
		self.trail = {self.pos.x, self.pos.y}
	end,
	update = function (self, dt)
		self.vel.y = self.vel.y + 100*dt*dt
		self.trail[#self.trail + 1] = self.pos.x
		self.trail[#self.trail + 1] = self.pos.y
	end,
	draw = function (self)
		--local endp = self.pos - self.vel / 2
		love.graphics.setColor(255, 255, 255)
		love.graphics.line(self.trail)
	end,
	death = function (self)
		local color = {math.random() * 255, math.random() * 255, math.random() * 255}
		for i = 1, 1000 do
			local ang, vel = math.random() * 2 * math.pi, math.random() * 500
			vel = Vector(math.sin(ang), math.cos(ang)) * vel
			self.emitter:create(self.pos, {
				vel = vel,
				lifetime = 5 + math.random() * 3,
				color = color
			})
		end
		love.audio.play(self.sound)
	end
}

local explosions, rockets, boom, nr

function love.load()
	explosions = ParticleSystem(Explosion)
	rockets = ParticleSystem(Rocket)
	boom = love.sound.newSoundData("explosion.ogg")
	nr = 0
end

function love.update(dt)
	if nr < love.timer.getMicroTime() then
		local mpos, spos, ttl = Vector(50 + math.random() * (love.graphics.getWidth() - 100), 50 + math.random() * 100), Vector(math.random() * love.graphics.getWidth(), love.graphics.getHeight()), 3 + math.random() * 2
		rockets:create(spos, {
			emitter = explosions,
			vel = (mpos - spos) / ttl,
			lifetime = ttl,
			sound = love.audio.newSource(boom)
		})
		nr = love.timer.getMicroTime() + math.random() * 3
	end
	explosions:think(dt)
	explosions:trim()
	rockets:think(dt)
	rockets:trim()
end

function love.draw()
	rockets:draw()
	explosions:draw()
end

function love.mousepressed(x, y, button)
	local mpos, spos, ttl = Vector(x, y), Vector(math.random() * love.graphics.getWidth(), love.graphics.getHeight()), 3 + math.random() * 2
	rockets:create(spos, {
		emitter = explosions,
		vel = (mpos - spos) / ttl,
		lifetime = ttl,
		sound = love.audio.newSource(boom)
	})
end