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doc: foot.1: XTGETTCAP

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Daniel Eklöf 2022-01-14 13:36:31 +01:00
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@ -373,6 +373,53 @@ distro package for foot's terminfo entries, you can install foot's
terminfo entries manually, by copying *foot* and *foot-direct* to
*~/.terminfo/f/*.
# XTGETTCAP
*XTGETTCAP* is an escape sequence initially introduced by XTerm, and
also implemented (and extended, to some degree) by Kitty.
It allows querying the terminal for terminfo classic, file-based,
terminfo definition. For example, if all applications used this
feature, you would no longer have to install foot’s terminfo on remote
hosts you SSH into.
XTerm’s implementation (as of XTerm-370) only supports querying key
(as in keyboard keys) capabilities, and three custom capabilities:
- TN - terminal name
- Co - number of colors (alias for the colors capability)
- RGB - number of bits per color channel (different semantics from
the RGB capability in file-based terminfo definitions!).
Kitty has extended this, and also supports querying all integer and
string capabilities.
Foot supports this, and extends it even further, to also include
boolean capabilities. This means foot’s entire terminfo can be queried
via *XTGETTCAP*.
Note that both Kitty and foot handles responses to multi-capability
queries slightly differently, compared to XTerm.
XTerm will send a single DCS reply, with ;-separated
capability/value pairs. There are a couple of issues with this:
- The success/fail flag in the beginning of the response is always 1
(success), unless the very first queried capability is invalid.
- XTerm will not respond at all to an invalid capability, unless it’s
the first one in the XTGETTCAP query.
- XTerm will end the response at the first invalid capability.
In other words, if you send a large multi-capability query, you will
only get responses up to, but not including, the first invalid
capability. All subsequent capabilities will be dropped.
Kitty and foot on the other hand, send one DCS response for each
capability in the multi query. This allows us to send a proper
success/fail flag for each queried capability. Responses for all
queried capabilities are always sent. No queries are ever dropped.
# ENVIRONMENT
The following environment variables are used by foot: