Synchronized Output
Synchronized output is merely implementing the feature as inspired by iTerm2 synchronized output,
except that it's not using the rare DCS but rather the well known SM ? and RM ?. iTerm2 has now also adopted to use the new syntax instead of using DCS.
Semantics
When rendering the screen of the terminal, the Emulator usually iterates through each visible grid cell and renders its current state. With applications updating the screen at a high frequency, this can cause tearing.
This mode attempts to mitigate that.
When the synchronization mode is enabled following render calls will keep rendering the last rendered state. The terminal Emulator keeps processing incoming text and sequences. When the synchronized update mode is disabled, the renderer may fetch the latest screen buffer state, effectively avoiding the tearing effect by unintentionally rendering in the middle of an application screen update.
Feature detection
Use CSI ? 2026 $ p to query the state of the (DEC) mode 2026. This works for any private mode number.
If you get nothing back (DECRQM not implemented at all) or you get back a CSI ? 2026 ; 0 $ y
then synchronized output is not supported.
See DECRQM (request)
and DECRPM (response) for more details.
DECRPM can respond with different values.
| Value | Documentation | Relevance for synchronized output mode ?2026 |
|---|---|---|
0 |
Mode is not recognized | not supported |
1 |
Set | supported and screen updates are not shown to the user until mode is disabled |
2 |
Reset | supported and screen updates are shown as usual (e.g. as soon as they arrive) |
3 |
Permanently set | undefined |
4 |
Permanently reset | not supported |
Using the feature
Use CSI ? 2026 h to enable batching output commands into a command queue.
Use CSI ? 2026 l when done with your current frame rendering, implicitly updating the render state by reading out the latest grid buffer state.
Notation
Some developers name the beginning and end of such a synchronized frame (and therefore the instance)
BSU(begin synchronized update,CSI ? 2026 h), andESU(end synchronized update,CSI ? 2026 l).
Timeout
So far there is no real consensus on weather a timeout should be and, if so, for how long. The toolkit/application implementer should keep this in mind. However, a too short timeout (maybe due to a very slow connection) won't be worse than having no synchronized output at all.
Adoption State
| Support | Terminal/Tookit/App | Notes |
|---|---|---|
| n/a | xterm.js | see tracker xterm.js#3375 |
| not yet | Windows Terminal | Proof-of-concept implementation by @j4james exists; tracker: wt#8331 |
| ✅ | Contour | |
| ✅ | mintty | |
| ✅ | Jexer | |
| ✅ | notcurses | see tracker: notcurses#1582 |
| ✅ | foot | terminal emulator https://codeberg.org/dnkl/foot |
| ✅ | Wezterm | see tracker: wezterm#882 |
| not yet | VTE / gnome-terminal | see tracker: gitlab/vte#15 |
| ✅ | iTerm2 | |
| ✅ | Kitty | since 5768c54c5b5763e4bbb300726b8ff71b40c128f8 |
| planned | Warp | see tracker: https://github.com/warpdotdev/Warp/issues/2185 |
| unknown | Alacritty | |
| unknown | Konsole | |
| unknown | urxvt | |
| unknown | st |
In case some project is adding support for this feature, please leave a comment or contact me, so we can keep the spec and implementation state table up to date.
Reference
The original document of this page was stored here.