UIs

Most UI is a poor fit for the simulation World. Menus, IMGUI debug panels, a pause overlay, the window itself — keep those in LÖVE (or a UI library) and push a thin event when the game must react.

Outside the World

function PauseMenu:draw ()
  -- SUIT / IMGUI / your own rects. Not a Concord System.
end

function love.keypressed (key)
  if key == "escape" then
    paused = not paused
    world:emit("paused", paused)
  end
end

function Body:paused (isPaused)
  self:setEnabled(not isPaused)
end

The menu does not need a Filter. The World only needs to know “simulation is paused.” setEnabled on the sim Systems is usually enough; you can keep a Hud System enabled so the overlay still draws.

Input follows the same direction: LÖVE callbacks → World:emit ("mousepressed", "textinput"). Do not poll love.mouse from every widget Component.

When UI is Entities

World-space health bars, floating damage numbers, inventory slots that are items in the World — those want Filters.

Two layouts:

• Same World, a flag. {"widget", "position"} versus {"widget", "!worldspace"}. Cheap, and the HUD can read health directly.
• A second World. Isolation is the feature; sharing “the player” then goes through a resource or a key you copy in.

Prefer enable/disable on a Hud System over destroying widgets every time the menu closes.

If you are writing a UI library on top of Concord, beforeEmit / afterEmit can wrap layout and input. See Before and After Events.

See also

• Worlds Guide
• Making a game with Concord and LÖVE