particles.p8

-- class maker
function class(proto, base)
 proto = proto or {}
 proto.__index = proto
 setmetatable(proto, {
  __index = base,
  __call = function(cls, ...)
   local self = setmetatable({
    type=proto
   }, proto)
   if(self.init) self:init(...)
   return self
  end
 })
 proto.subclass = function(subproto)
  return class(subproto, proto)
 end
 return proto
end

--------------------------------
-- particles
--------------------------------

partgen=class()

function partgen:init(args)
 -- required args
 self.x=args.x
 self.y=args.y

 -- optional args
 self.colors=args.colors or {args.color} or {7}
 self.dur=args.duration or maxnum
 self.rate=args.rate or 10
 self.pdur=args.partduration or .2
 self.actor=args.actor

 self.particles={}
 self.age=0
 self.pcount=0
end

-- have i finished drawing
function partgen:done()
 return self.age>self.dur and #self.particles<=0
end

function partgen:stop()
 self.dur=0
end

function partgen:newpart()
 local p={
  x=self.x, y=self.y,
  c=rndchoice(self.colors),
  vel={x=rnd(200)-100, y=-rnd(100)},
  age=0,
 }
 if self.actor then
  p.x+=self.actor.x
  p.y+=self.actor.y
 end
 return p
end

function partgen:update()
 if self.age<=self.dur then
  self.age+=dt
  while self.pcount < self.rate*self.age do
   add(self.particles, self:newpart())
   self.pcount+=1
  end
 end

 for p in all(self.particles) do
  p.age+=dt
  if p.age>=self.pdur then
   del(self.particles, p)
  else
   p.x+=p.vel.x*dt
   p.y+=p.vel.y*dt
   p.vel.y+=g*dt
  end
 end
end

function partgen:draw(o)
 for p in all(self.particles) do
  pset(p.x, p.y, p.c)
 end
end

--------------------------------
-- example usage
--------------------------------

-- table containing all known particle generators
local particles = {}

-- create particle system for water splashes (short duration, shades of blue)
add(particles, partgen{
  x=self.x+4, y=self.y+4,
  colors={7,12,1,13},
  duration=0.1,
  rate=20,
})

function _update()
  -- update states & positions of particles
  for p in all(particles) do
    p.update()
  end
end

function _draw()
  -- draw
  for p in all(particles) do
    p.draw()
  end
end