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Graphics protocol: note best detection method

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Per https://github.com/kovidgoyal/kitty/issues/2636#issuecomment-626467852
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Fredrick Brennan 2020-05-10 23:02:12 -07:00 committed by GitHub
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docs/graphics-protocol.rst
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@ -262,8 +262,8 @@ received. Finally, terminals must not display anything, until the entire sequenc
received and validated.
Detecting available transmission mediums
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Querying support and available transmission mediums
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Since a client has no a-priori knowledge of whether it shares a filesystem/shared memory
with the terminal emulator, it can send an id with the control data, using the ``i`` key
@ -289,6 +289,31 @@ use the *query action*, set ``a=q``. Then the terminal emulator will try to load
the image and respond with either OK or an error, as above, but it will not
replace an existing image with the same id, nor will it store the image.
While as of May 2020, Kitty is the only terminal emulator to support its
graphics protocol, we intend that any terminal emulator that wishes to support
it can. While one could send `Device Control String (DCS)
<https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h3-Device-Control-functions>`_
XTGETTCAP TN, this would require that derivatives of Kitty also report a
terminfo name containing at least `kitty`. Therefore, the recommended procedure
for querying support is:
* Send e.g.::
<ESC>_Gi=31,s=1,v=1,a=q,t=d,f=24;<NUL><NUL><NUL><ESC>\
* Immediately after, send anything else that will block the terminal, such as,
perhaps, XTGETTCAP TN (``544e``)::
<ESC>P+q544e<ESC>\
* See what you get back first. If you get back the XTGETTCAP reply, Kitty
graphics are not supported. If you get the APC reply from Kitty
(``<ESC>_Gi=31;OK<ESC>\``), they are. You can therefore query both support
and transmission medium at the same time, as even errors indicate support.
In order for this detection method to work, Kitty graphics standard-compliant
emulators may handle all escape codes in a first-in-first-out (FIFO) fashion,
but **must** at least always immedidately block upon receiving an APC ``G``
request with ``a=q``.
Display images on screen
-----------------------------