Stabilize the LÖVR physics and state updates by running them at consistent intervals regardless of frame rate

cycles.lua

-- require this file to have reduced input lag and game logic that runs consistently
-- inspired by https://gafferongames.com/post/fix_your_timestep/
-- note: this decouples update() from draw(); update() can run multiple times per frame

local m = {}

m.update_delta = 1 / 60

function lovr.run()
  if lovr.timer then lovr.timer.step() end
  if lovr.load then lovr.load(arg) end
  local current_time = 0.0
  local accumulator = 0.0
  local t = 0.0
  local previous_state = {}
  local current_state = {}
  return function()
    local dt = m.update_delta
    local window
    if lovr.graphics then -- get window pass earlier than LÖVR default to reduce input lag
      window = lovr.graphics.getWindowPass()
    end
    if lovr.system then lovr.system.pollEvents() end
    if lovr.event then
      for name, a, b, c, d in lovr.event.poll() do
        if name == 'restart' then return 'restart', lovr.restart and lovr.restart()
        elseif name == 'quit' and (not lovr.quit or not lovr.quit(a)) then return a or 0
        elseif name ~= 'quit' and lovr.handlers[name] then lovr.handlers[name](a, b, c, d) end
      end
    end

    if lovr.timer then lovr.timer.step() end
    if lovr.headset and lovr.headset.isActive() then lovr.headset.update() end
    local new_time = lovr.timer.getTime()
    local frame_time = new_time - current_time
    if frame_time > 0.25 then frame_time = 0.25 end
    current_time = new_time
    accumulator = accumulator + frame_time
    while accumulator >= dt do
      previous_state = current_state
      if lovr.update then lovr.update(dt, t) end
      t = t + dt
      accumulator = accumulator - dt
    end
    local alpha = accumulator / dt
    local state = {}
    for k, v in pairs(current_state) do
      state[k] = v * alpha + previous_state[k] * (1.0 - alpha)
    end
    if lovr.graphics then
      local headset = lovr.headset and lovr.headset.getPass()
      if headset and (not lovr.draw or lovr.draw(headset, state)) then headset = nil end
      if window and (not lovr.mirror or lovr.mirror(window, state)) then window = nil end
      lovr.graphics.submit(headset, window)
      lovr.graphics.present()
    end
    if lovr.headset then lovr.headset.submit() end
    if lovr.math then lovr.math.drain() end
  end
end

return m