ECS in P8 ✨

hello.p8

pico-8 cartridge // http://www.pico-8.com
version 16
__lua__
--pecs - pico-8 ecs
--01010111

function _init()
	local rect = get_id()
	add_component(rect, 'position', { x=60, y=60 })
	add_component(rect, 'physics', { vx=2, vy=0, ax=0, ay=2, dx=0.9, dy=1.0 })
	add_component(rect, 'drawable', { w=8, h=8, c=3 })
end

function _update()
	update_physics(get_entities_with_components({'position', 'physics'}))
end

function _draw()
	cls()
	draw_entities(get_entities_with_components({'drawable', 'position'}))
end

function update_physics(eids)
	for e in all(eids) do
		local phys = components['physics'][e]
		local pos = components['position'][e]
		phys.vx += phys.ax
		phys.vy += phys.ay
		phys.ax *= phys.dx
		phys.ay *= phys.dy
		pos.x += phys.vx
		pos.y += phys.vy
		if pos.x < 0 then phys.vx = abs(phys.vx) end
		if pos.x > 128 then phys.vx = abs(phys.vx) * -1 end
		if pos.y > 120 then phys.vy = -20 end
	end
end

function draw_entities(eids)
	for e in all(eids) do
		local rend = components['drawable'][e]
		local pos = components['position'][e]
		rectfill(pos.x, pos.y, pos.x + rend.w, pos.y + rend.h, rend.c)
	end
end

-->8
-- ecs framework
-- entities

next_id = 1

function get_id()
	next_id += 1
	return next_id - 1
end

-- components

components = {}

function add_component(e, cid, cdata)
	if (components[cid] == null) then components[cid] = {} end
	components[cid][e] = cdata
end

-- systems

function get_entities_with_component(id)
	local eids = {}
	local n = 0
	for k,v in pairs(components[id]) do
		n += 1
		eids[n] = k
	end
	return eids
end

function get_entities_with_components(ids)
	local eids = get_entities_with_component(ids[1])
	if (#eids == 0) return {}
	for id in all(ids) do
		local teids = get_entities_with_component(id)
		if (#teids == 0) return {}
		eids = intersection(eids, teids)
	end
	return eids
end

-->8
-- utilities
-- table utils

function has_element(t, e)
	for o in all(t) do if (o == e) then return true end end
	return false
end

function intersection(t1, t2)
	local i = {}
	for e in all(t1) do if has_element(t2, e) then add(i, e) end end
	return i
end