Using fixed time step updates makes visual stuttering of moving objects.

[dawidkomorowski]

When handling movement of objects in fixed time step updates there is observable visual stuttering. Reason for that is variable number of fixed time steps per frame - from zero to many. There are couple of options how to approach the issue:

• Have all the logic in variable time step updates
  • not good for physics stability and in general it is non deterministic approach
  • requires that all systems are able to run in variable time step mode (does not seem very problematic if deterministic results are not expected)
  • may be good enough for many single player games and some multiplayer games
• Semi fixed time step
  • mostly similar to variable time step solution as it still results in non deterministic updates
  • limits the inaccuracy of simulation by introducing maximum time step so the time step is variable as long as it is below the maximum allowed, if it is above the limit then multiple steps with the size of maximum allowed are performed
  • may require new specialized method i.e. SemiFixedUpdate(GameTime deltaTime) not to confuse the behavior of different updates methods (Update: once per frame, SemiFixedUpdate: at least once per frame, FixedUpdate: zero or more per frame)
  • may be good enough for majority of single player and multiplayer games
• Interpolation based rendering
  • visuals are one frame behind simulation and based on time left to simulate the state to present is interpolated between last simulation update and current simulation update
  • seems to be very complex to implement
  • works perfectly for complex physics games and determinism requiring games

Definition of Done

• [ ] Automated Tests - new and modified code is covered with automated tests
• [ ] Documentation - new and modified APIs are documented
• [ ] Performance - performance is verified to avoid regression
• [ ] Compatibility - consider compatibility of APIs and functionality with previous version and provide upgrade path if possible
• [ ] Demo Application - if new functionality should be showcased in Demo Application or existing functionality changed update Demo Application
• [ ] Release Activities - if release process is affected update Release Activities issue template

[dawidkomorowski]

Notice: Sound playback may have some impact on this. In TestGame it sometimes feels like starting playback of new sounds has an impact on the scale of the problem. Maybe starting a sound playback is costly and takes quite a lot of time until it is moved to audio thread.