Targeted Emits

If you named the System, you can address it:

local Movement = Concord.System("Movement", {
  animals = { "terrestrial", "position" }
})

-- ...
world:emit("Movement.update", dt)

"Movement.update" runs Movement:update and nobody else’s update. The name is the string you passed to Concord.System("Movement", ...). An unnamed System cannot be targeted this way.

Use a targeted emit when a global event would wake Systems that should not care. “The player clicked this Entity” is often world:emit("Select.select", entity) rather than a clicked flag every Render System has to ignore.

The other way to isolate work is a flag Component plus a Filter. Prefer the Filter when many Entities share the behavior. Prefer a targeted emit when the audience is one System.

Payloads

Extra arguments are the payload:

world:emit("mousepressed", x, y, button)

function Select:mousepressed (x, y, button)
  -- ...
end

Pass dt, mouse coordinates, the Entity that was hit. Do not stuff those into a dummy Entity just to make an event look like ECS.

Emitting from a System

function Combat:update ()
  -- ...
  self:getWorld():emit("playSound", "hit")
end

A nested emit runs immediately. Swallowing, logging, or wrapping every emit is not a targeted emit — that is Before and After Events.

See also

• World:emit
• Worlds Guide
• Before and After Events