particles.p8

pico-8 cartridge // http://www.pico-8.com
version 32
__lua__
#include ../pecs.lua
--include"../pecs.lua" -- picotron

-- A particle emitter example showing how to use PECS (PICO-8 Entity Component
-- System) by Jess Telford: https://github.com/jesstelford/pico-8-pecs
-- This example is optimised for readability, not token or character count.
-- License: MIT Copyright (c) 2021 Jess Telford

-------------------
--[[ ECS SETUP ]]--

-- Setup the world where all Components, Entities, and Systems will live
local world = pecs()

--[[ END ECS SETUP ]]--
-----------------------

------------------------
--[[ ECS COMPONENTS ]]--

-- Create instantiable Components with default values
-- These values will all be used later in the Systems
-- Individual values can be overriden when instiating a Component
local Position = world.component({ x= 0, y = 0 })
local Velocity = world.component({ x= 0, y = 0 })
local Acceleration = world.component({ x = 0, y = 60 })
local Renderable = world.component({ color = 7, size = 1 })
local Ttl = world.component({ ttlSeconds = 0 })
-- One Component to store general emitter data
local Emitter = world.component({
  isEmitting = false,
  emitAt = 0
})
-- Other components used to determine the exact type of emitter
local FountainEmitter = world.component({ emitEverySeconds = 0.01 })
local RainfallEmitter = world.component({ emitEverySeconds = 0.01 })
local ExplosionEmitter = world.component({ emitEverySeconds = 0.01 })

--[[ END ECS COMPONENTS ]]--
----------------------------

function _init()
  -- Setup our emitter.
  -- Systems which filter for these components will be automatically updated to
  -- include this new entity.
  world.entity(
    {},
    Emitter(),
    -- Start with a Fountain, but it can be changed based on input
    FountainEmitter(),
    Position({ x = 64, y = 64 }),
    Renderable({ color = 7, size = 2 })
  )
end

---------------------
--[[ ECS SYSTEMS ]]--

-- A System for handling input. In this example, we only have a single entity
-- which matches the filter { Emitter, Position }, so this System could be
-- replaced with a regular function.
-- But, as our world grows, we may want more than one emitter which responds to
-- user input. All that's required is to call `world.entity` with at least
-- the `Emitter` & `Position` components, then this System will automatically
-- detect it and run the function.
--
-- To try it out; duplicate the `world.entity` call in _init() above, but
-- with a different type and x/y value.
local handleEmitterInput = world.system({ Emitter, Position }, function(emitter, tickTime)
  -- Move the emitter around while keeping it on the screen
  if (btn(0)) then emitter[Position].x = (emitter[Position].x - 1) % 128 end
  if (btn(1)) then emitter[Position].x = (emitter[Position].x + 1) % 128 end
  if (btn(2)) then emitter[Position].y = (emitter[Position].y - 1) % 128 end
  if (btn(3)) then emitter[Position].y = (emitter[Position].y + 1) % 128 end

  -- Remove the current emitter and add a new emitter
  if (btnp(4)) then
    if (emitter[FountainEmitter]) then
      emitter -= FountainEmitter
      emitter += RainfallEmitter()
    elseif (emitter[RainfallEmitter]) then
      emitter -= RainfallEmitter
      emitter += ExplosionEmitter()
    elseif (emitter[ExplosionEmitter]) then
      emitter -= ExplosionEmitter
      emitter += FountainEmitter()
    end
  end

  -- Turn the emitter on
  if (btn(5)) then
    -- If it was previously not emitting
    if (not emitter[Emitter].isEmitting) then
      -- Reset the next emission time
      emitter[Emitter].emitAt = tickTime
    end

    emitter[Emitter].isEmitting = true
  else
    emitter[Emitter].isEmitting = false
  end
end)

-- The following Systems have a similar filter to the `handleEmitterInput`
-- System, so why not combine them?
-- Because they serve different purposes.
-- In this example, the emitter is controlled with input, but in another
-- program, the emitter might not be controllable at all, or there may be
-- multiple emitters controlled differently (eg: A steam train puffing smoke
-- goes past a camp fire).
-- ie; this system shouldn't know or care about user input. There could be other
-- systems that modify emitters (on/off, movement, etc) that have nothing to do
-- with input. This system only cares about emitting.
local emitFountain = world.system({ Emitter, FountainEmitter, Position }, function(emitter, tickTime)
  if (not emitter[Emitter].isEmitting) then return end

  -- Make sure enough time has elapsed to emit a new particle
  -- And keep emitting until we've caught up in time
  while (tickTime >= emitter[Emitter].emitAt) do
    emitter[Emitter].emitAt += emitter[FountainEmitter].emitEverySeconds

    -- 0.25 is 90deg counter-clockwise, so this points it straight up
    -- 0.125 is 45deg
    -- -0.0625 is to rotate it back by half that (-22.5deg) so it's not
    -- lop-sided
    local angle = 0.25 + rnd(0.125) - 0.0625
    local speed = 50 + rnd(30)

    world.entity(
      {},
      Position({ x=emitter[Position].x, y=emitter[Position].y }),
      Velocity({ x = cos(angle) * speed, y = sin(angle) * speed }),
      Acceleration(), -- Default accel values
      Renderable({ color = 8 + rnd(8) }),
      Ttl({ ttlSeconds = 2 + rnd(3) })
    )
  end
end)

local emitRainfall = world.system({ Emitter, RainfallEmitter, Position }, function(emitter, tickTime)
  if (not emitter[Emitter].isEmitting) then return end

  -- Make sure enough time has elapsed to emit a new particle
  -- And keep emitting until we've caught up in time
  while (tickTime >= emitter[Emitter].emitAt) do
    emitter[Emitter].emitAt += emitter[RainfallEmitter].emitEverySeconds

    world.entity(
      {},
      Position({ x=emitter[Position].x + rnd(40) - 20, y=emitter[Position].y }),
      Velocity(),
      Acceleration(), -- Default accel values
      Renderable({ color = 8 + rnd(8) }),
      Ttl({ ttlSeconds = 2 + rnd(3) })
    )
  end
end)

local emitExplosion = world.system({ Emitter, ExplosionEmitter, Position }, function(emitter, tickTime)
  if (not emitter[Emitter].isEmitting) then return end

  -- Make sure enough time has elapsed to emit a new particle
  -- And keep emitting until we've caught up in time
  while (tickTime >= emitter[Emitter].emitAt) do
    emitter[Emitter].emitAt += emitter[ExplosionEmitter].emitEverySeconds

    local angle = rnd(1)
    local speed = 50 + rnd(30)

    world.entity(
      {},
      Position({ x=emitter[Position].x, y=emitter[Position].y }),
      Velocity({ x = cos(angle) * speed, y = sin(angle) * speed }),
      Acceleration({ x = 0, y = 0 }),-- Overwrite the defaults
      Renderable({ color = 8 + rnd(8) }),
      Ttl({ ttlSeconds = 2 + rnd(3) })
    )
  end
end)

-- Particles don't live forever, so we give them a TTL
local ttlUpdate = world.system({ Ttl }, function(item, tDiff)
  item[Ttl].ttlSeconds -= tDiff

  -- Once their remaining TTL is up
  if (item[Ttl].ttlSeconds <= 0) then
    -- Remove that entity from the world.
    -- All Systems will be automatically updated to exclude this item
    world.remove(item)
  end
end)

-- A mini physics system
local moveItems = world.system({ Position, Velocity, Acceleration }, function(item, tDiff)
  item[Velocity].x += tDiff * item[Acceleration].x
  item[Velocity].y += tDiff * item[Acceleration].y
  item[Position].x += tDiff * item[Velocity].x
  item[Position].y += tDiff * item[Velocity].y
end)

-- Very naive rendering in this example. As complexity rises, it makes sense to
-- create Components for each type of renderable, and the System which actually
-- does the rendering.
local drawRenderables = world.system({ Position, Renderable }, function(renderable)
  circfill(
    renderable[Position].x,
    renderable[Position].y,
    renderable[Renderable].size,
    renderable[Renderable].color
  )
end)

--[[ END ECS SYSTEMS ]]--
-------------------------

---------------------
--[[ PICO8 LOOPS ]]--

local lastTickTime = time()
function _update60()
  local tickTime = time()
  local tDiff = tickTime - lastTickTime
  -- Important to call .update() at the start of every loop, before any Systems
  world.update()
  -- The parameters passed in here will appear as the second argument in the
  -- System's function
  ttlUpdate(tDiff)
  handleEmitterInput(tickTime)
  emitFountain(tickTime)
  emitRainfall(tickTime)
  emitExplosion(tickTime)
  moveItems(tDiff)
  lastTickTime = tickTime
end

-- picotron
if (_G) _update = _update60

function _draw()
  cls(0)
  drawRenderables()
  print("\f7  move   emit type", 2, 2)
  print("\f7"..chr(139,145,148,131).."  "..chr(151).."   "..chr(142), 2)
end

--[[ END PICO8 LOOPS ]]--
-------------------------
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