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Fixing jitter, stutter and input lag

What is jitter, stutter and input lag?

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.

Input lag is unrelated to jitter and stutter, but is sometimes discussed alongside. Input lag refers to visible on-screen delay when performing actions with the mouse, keyboard, controller or touchscreen. It can be related to game code, engine code or external factors (such as hardware). Input lag is most noticeable in games that use the mouse to aim, such as first-person games. Input lag can't be completely eliminated, but it can be reduced in several ways.

Distinguishing between jitter and stutter

A game running at a normal framerate without exhibiting any effect will appear smooth:

A game exhibiting jitter will shake constantly in a very subtle way:

Finally, a game exhibiting stutter will appear smooth, but appear to stop or roll back a frame every few seconds:

Jitter

There can be many causes of jitter, the most typical one happens when the game physics frequency (usually 60 Hz) runs at a different resolution than the monitor refresh rate. Check whether your monitor refresh rate is different from 60 Hz.

This is generally not a problem, given that most monitors are 60 Hz, and starting with Godot 3.1, a frame timer was introduced that tries to synchronize with refresh as well 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.

Note

You can use physics interpolation to mitigate physics-related jittering. See lawnjelly's smoothing-addon for an add-on that can be dropped into any project to enable physics interpolation.

Stutter

Stutter may happen due to two different reasons. 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.

On platforms that support disabling V-Sync, stuttering can be made less noticeable by disabling V-Sync in the project settings. This will however cause tearing to appear, especially on monitors with low refresh rates. If your monitor supports it, consider enabling variable refresh rate (G-Sync/FreeSync) while leaving V-Sync enabled. This avoids mitigating some forms of stuttering without introducing tearing.

Forcing your graphics card to use the maximum performance profile can also help reduce stuttering, at the cost of increased GPU power draw.

Windows

Windows is known to cause stutter in windowed games. This mostly depends on the hardware installed, drivers version and processes running in parallel (e.g. having many browser tabs open may cause stutter in a running game). To avoid this, starting with 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 to live with this problem, as it is common for Windows games and most users won't play games windowed (games that are played in a window, e.g. puzzle games, will usually not exhibit this problem anyway).

For fullscreen, Windows gives special priority to the game so stutter is no longer visible and very rare. This is how most games are played.

Linux

Stutter may be visible on desktop Linux, but this is usually associated with different video drivers and compositors. Some compositors may also trigger this problem (e.g. KWin), so it is advised to try using a different one to rule it out as the cause. Some window managers such as KWin and