DearImGui.withWindowOpen "Orbit" do
  stuff <- atomically . Apecs.runWith rsOrbitSim.sWorld $ Apecs.collect Just
  for_ stuff \(o@Orbiter.Orbiter{}, Orbiter.MeanAnomaly ma, entity@Apecs.Entity{}) -> do
    DearImGui.text $ textShower o
    inputDouble "MA" (ma # Radian) (τ/60) (τ/4) "%f rad" \ma' -> do
      atomically . Apecs.runWith rsOrbitSim.sWorld $ do
        -- XXX: unlikely, but the value may be updated between collecting and UI handling
        let change = (ma' % Radian) |-| ma
        Apecs.modify entity \(Orbiter.MeanAnomaly current) ->
          Orbiter.MeanAnomaly $ current |+| change

inputOrbitElem rsOrbitSim entity "Eccentricity" (o.orbit.eccentricity # Number) (1/256) (1/8) "%.5f" \ecc' ->
  Orbiter.eccentricity .~ (ecc' % Number)

inputOrbitElem rsOrbitSim entity "Periapsis" ((o.orbit.periapsis # Meter) / 1000) 1 10 "%.1f km" \p' ->
  Orbiter.periapsis .~ ((p' * 1000) % Meter)

-- ...