From b744faa2e42ed37459fe3edb69c1149146233e5b Mon Sep 17 00:00:00 2001
From: ne_mene <borna.ozanic@gmail.com>
Date: Sun, 8 Mar 2026 22:21:42 +0100
Subject: let there be light

---
 src/ecs.lua | 169 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 169 insertions(+)
 create mode 100644 src/ecs.lua

(limited to 'src/ecs.lua')

diff --git a/src/ecs.lua b/src/ecs.lua
new file mode 100644
index 0000000..1df5421
--- /dev/null
+++ b/src/ecs.lua
@@ -0,0 +1,169 @@
+
+local current_scene = nil
+local compfuncs = {}
+
+function TAGCOMP(_) end
+
+function new_scene()
+  local newscene = {
+    compmask = {},
+    entities = {},
+    entities_size = 0,
+
+    free_entids = {},
+    free_entids_size = 0,
+
+    killset = {},
+    killq = {},
+    killq_size = 0,
+
+    -- Events
+    on_draw = new_event(),
+    on_update = new_event(),
+
+    comp_removeq = {},
+    comp_entq = {},
+    comp_removeq_size = 0,
+  }
+  for comp, _ in pairs(compfuncs) do
+    newscene.compmask[comp] = {
+      sparse = {},
+      dense = {},
+      size = 0,
+    }
+  end
+  return newscene
+end
+
+function set_scene(newscene)
+  current_scene = newscene
+end
+
+function get_current_scene()
+  return current_scene
+end
+
+function register_comp(name, func)
+  assert(compfuncs[name] == nil, "Component '"..name.."' is already registered.")
+
+  compfuncs[name] = func
+end
+
+function add_comp(ent, comp, ...)
+  assert(current_scene, "No scene up.")
+  assert(compfuncs[comp], "Unknown component '"..tostring(comp).."'")
+  assert(current_scene.entities[ent.id], "Entity "..tostring(ent.id).." doesn't exist.")
+
+  local mask = current_scene.compmask[comp]
+  assert(not mask.sparse[ent.id], "Entity "..tostring(ent.id).." already has component of type '"..comp.."'.")
+
+  mask.size = mask.size + 1
+  mask.sparse[ent.id] = mask.size
+  mask.dense[mask.size] = ent.id
+
+  compfuncs[comp](current_scene.entities[ent.id], ...)
+end
+
+local function remove_comp(ent, comp)
+  assert(current_scene, "No scene up.")
+  assert(compfuncs[comp], "Unknown component '"..tostring(comp).."'")
+  assert(current_scene.entities[ent.id], "Entity "..tostring(ent.id).." doesn't exist.")
+
+  local mask = current_scene.compmask[comp]
+  assert(mask.sparse[ent.id], "Entity "..tostring(ent.id).." does not have component of type '"..comp.."'.")
+
+  local index = mask.sparse[ent.id]
+  local lastid = mask.dense[mask.size]
+
+  mask.sparse[ent.id] = nil
+  mask.sparse[lastid] = index
+
+  mask.dense[index] = mask.dense[mask.size]
+  mask.dense[mask.size] = nil
+  mask.size = mask.size - 1
+end
+
+function run_system(comp, func, ...)
+  assert(current_scene, "No scene up.")
+  assert(compfuncs[comp], "Unknown component '"..tostring(comp).."'")
+
+  for _, entid in ipairs(current_scene.compmask[comp].dense) do
+    func(current_scene.entities[entid], ...)
+  end
+end
+
+function queue_entity_kill(ent)
+  assert(current_scene, "No scene up.")
+  assert(current_scene.entities[ent.id], "Entity "..tostring(ent.id).." doesn't exist.")
+
+  if current_scene.killset[ent.id] then
+    return
+  end
+  current_scene.killset[ent.id] = true
+  current_scene.killq_size = current_scene.killq_size + 1
+  current_scene.killq[current_scene.killq_size] = ent.id
+end
+
+function has_comp(ent, comp)
+  assert(current_scene, "No scene up.")
+  assert(compfuncs[comp], "Unknown component '"..tostring(comp).."'")
+  assert(current_scene.entities[ent.id], "Entity "..tostring(ent.id).." doesn't exist.")
+
+  return current_scene.compmask[comp].sparse[ent.id] ~= nil
+end
+
+function queue_remove_comp(ent, comp)
+  assert(current_scene, "No scene up.")
+  assert(compfuncs[comp], "Unknown component '"..tostring(comp).."'")
+
+  if not has_comp(ent, comp) then return end
+
+  current_scene.comp_removeq_size = current_scene.comp_removeq_size + 1
+  current_scene.comp_removeq[current_scene.comp_removeq_size] = comp
+  current_scene.comp_entq[current_scene.comp_removeq_size] = ent
+end
+
+function flush_scene()
+  assert(current_scene, "No scene up.")
+
+  for i=1, current_scene.comp_removeq_size do
+    remove_comp(current_scene.comp_entq[i], current_scene.comp_removeq[i])
+  end
+  current_scene.comp_removeq_size = 0
+
+  for i=current_scene.killq_size, 1, -1 do
+    local ent = current_scene.entities[current_scene.killq[i]]
+    for comp, _ in pairs(current_scene.compmask) do
+      if has_comp(ent, comp) then
+        remove_comp(ent, comp)
+      end
+    end
+
+    current_scene.killset[ent.id] = nil
+
+    current_scene.free_entids_size = current_scene.free_entids_size + 1
+    current_scene.free_entids[current_scene.free_entids_size] = ent.id
+  end
+  current_scene.killq_size = 0
+end
+
+function new_entity()
+  assert(current_scene, "No scene up.")
+
+  if current_scene.free_entids_size > 0 then
+    local entid = current_scene.free_entids[current_scene.free_entids_size]
+    current_scene.free_entids_size = current_scene.free_entids_size - 1
+
+    local ent = current_scene.entities[entid]
+    for key in pairs(ent) do
+      ent[key] = nil
+    end
+    ent.id = entid
+    return ent
+  end
+  local newid = current_scene.entities_size + 1
+  current_scene.entities[newid] = {id = newid}
+  current_scene.entities_size = newid
+
+  return current_scene.entities[newid]
+end
-- 
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