Entity-component helpers for Pico-8

pico8_entity_component.lua

------------
-- object --
------------

-- base prototype
object={}
function object:new(o)
 o=o or {}
 setmetatable(o,self)
 self.__index=self
 return o
end

------------
-- entity --
------------

-- container for components
entity=object:new()

-- construct a new entity instance
function make_entity()
 return entity:new{
 	children={},
 	to_update={},
 	to_draw={}
 }
end

-- add a component instance
function entity:attach(c)
 self.children[c.id]=c
 c.parent=self
 if (c.update) add(self.to_update,c.id)
 if (c.draw) add(self.to_draw,c.id)
end

-- remove a component instance
function entity:detach(c)
 self.children[c.id]=nil
 c.parent=nil
 if (c.update) del(self.to_update,c.id)
 if (c.draw) del(self.to_draw,c.id)
end

-- retrieve a component instance
-- c is a component prototype
function entity:get(c)
 return self.children[c.id]
end

-- update all child components
function entity:update()
 for _,i in pairs(self.to_update) do
  self.children[i]:update()
 end
end

-- draw all child components
function entity:draw()
 for _,i in pairs(self.to_draw) do
  self.children[i]:draw()
 end
end

---------------
-- component --
---------------

-- base component prototype
component=object:new{
	id=nil
}

-- construct a new component instance
function make_component()
 return component:new{
  parent=nil,
 }
end

-- get another component on the same entity
function component:get(c)
 return self.parent:get(c)
end
        
------------
-- pico-8 --
------------

function _init()
 world={}
end

function _update()
 for _,e in pairs(world) do
  e:update()
 end
end

function _draw()
 cls()
 for _,e in pairs(world) do
  e:draw()
 end
 print_perf()
end

-- print performance stats
function print_perf()
 print("mem:"..stat(0))
 print("cpu:"..stat(1))
 print("sys:"..stat(2))
end