Add a short tutorial explaining how to fix (or report) jitter or stutter.

tutorials/misc/index.rst

@@ -5,6 +5,7 @@ Miscellaneous
    :maxdepth: 1
    :name: toc-learn-features-misc
 
+   jitter_stutter
    handling_quit_requests
    pausing_games
    binary_serialization_api

tutorials/misc/jitter_stutter.rst

@@ -0,0 +1,84 @@
+.. _doc_jitter_stutter:
+
+Fixing Jitter and Stutter
+==========================
+
+What are Jitter and Stutter?
+-----------------------------
+
+*Jitter* and *stutter* are two different alterations to visible motion of objects on screen that may affect a game, even when running at full speed. These effects are mostly visible in games where the world moves at a constant speed in a fixed direction, like runners or platformers.
+
+Distinguishing between them
+---------------------------
+
+A game running at a normal framerate without exhibiting any effect will appear smooth:
+
+.. image:: img/motion_normal.gif
+
+A game exhibiting *jitter* will shake constantly in a very subtle way:
+
+.. image:: img/motion_jitter.gif
+
+Finally, a game exhibiting *stutter* will appear smooth, but appear to *stop* or *roll back a frame* every a few seconds:
+
+.. image:: img/motion_stutter.gif
+
+
+Jitter
+-------
+
+There can be many causes of jitter, the most typical one happens when the game *physics frequency* (usually 60hz) runs at a different resolution than the monitor refresh rate. Check whether your monitor refresh rate is different than 60hz. 
+
+This is still generally not a problem, given refresh rates higher than 60hz are barely visible to the human eye and beginning Godot 3.1, a frame timer was introduced that tried to synchronize with refresh as best as possible.
+
+Sometimes only some objects appear to jitter (character or background). This happens when they are processed in different time sources (one is processed in the physics step while another is processed in the idle step). Godot 3.1 does some improvements to this, from allowing kinematic bodies to be animated in the regular _process loop, to further fixes in the frame timer.
+
+Stutter
+-------
+
+Stutter may happen due to two different reason. The first, and most obvious one, is the game not being able to keep full framerate performance. Solving this is game specific and will require optimization.
+
+The second is more complicated, because it is often not associated to the engine or game but the underlying operating system. Here is some information regarding stutter on different OSs.
+
+Windows
+^^^^^^^
+
+Windows is known to cause stutter in windowed games. This depends on the hardware installed and processes running mostly (many chrome tabs open may cause stutter in a running game). To avoid this, beginning 3.1, Godot raises the game priority to "Above Normal". This helps considerably but may not completely eliminate stutter. 
+
+Eliminating this completely requires giving your game full privileges to become "time critical", which is not advised. Some games may do it, but it is advised to learn live with this problem as it is usual for Windows games as most users won't play games windowed (games that are played in a window, usually puzzle games, will not exhibit this problem anyway).
+
+For full-screen, Windows gives special priority to the game so stutter is no longer visible and very rare. This is how most games are played.
+
+Linux (X11)
+^^^^^^^^^^^
+
+Stutter may be visible on Desktop Linux, but this is usually associated with different video drivers and compositors. Noveau drivers often exhibit this, while AMD or NVidia proprietery don't. Some compositors may also exhibit this problem, so it is advised to try using a different one to rule it out as the cause. 
+
+There is no workaround for driver or compositor stuttering other than reporting it as an issue to the developer.
+
+MacOS
+^^^^^
+
+Generally, MacOS is stuter free, although recently some bugs were reported when running on full-screen (this is a MacOS bug). If you have a machine exhibiting this behavior please let us know.
+
+
+Android
+^^^^^^^
+
+Generally, Android is stutter and jitter free because the running activity gets all the priority. That said, there may be problematic devices (Older Kindle Fire is known to be one). If you see this problem on Android, please let us know.
+
+iOS
+^^^
+
+iOS devices are generally stutter free, but older devices running newer versions of the operating system may exhibit problems. This is generally unavoidable.
+
+Reporting Stutter / Jitter problems
+-----------------------------------
+
+If you are reporting a stutter or jitter problem (opening an issue) not caused by any of the above reasons, please specify very clearly all the information possible about device, operating system, driver versions etc. This may help to better troubleshoot it.
+
+Also make sure to use the correct term (jitter or stutter) based on the exhibited behavior. This will help understand your issue much faster.
+
+
+
+