The keyboard interfaces and protocols in X

[John Found]

> And XKB is probably one of the most extensively documented protocols,

I don't know what "extensively" means in your understanding, but the
documentation of XKB is sloppily written. They even didn't labeled
the items in "Appendix D: Protocol encoding". Which is the main 
document if one have to implement the protocol in code.



On Wed, 16 Feb 2022 09:59:55 +1000
Peter Hutterer <peter.hutterer at who-t.net> wrote:

> On Tue, Feb 15, 2022 at 05:42:39PM +0200, John Found wrote:
> > On Tue, 15 Feb 2022 14:29:05 +0000
> > Dave Howorth <xorg at howorth.org.uk> wrote:
> >   
> > > On Tue, 15 Feb 2022 15:21:07 +0200
> > > John Found <johnfound at asm32.info> wrote:
> > >   
> > > > What is the meaning of the fields in the following structure,
> > > > in the XkbGetMap reply:
> > > > 
> > > > KB_KEYSYMMAP     8+4n
> > > > 4     LISTofCARD8    ktIndex      ; What is this?
> > > > 1     CARD8          groupInfo    ; What is this?    
> > > > 1     CARD8          width        ; Width of what?
> > > > 2     n              nSyms        ; more or less clear
> > > > 4n    LISTofKEYSYM          syms  ; clear as well.    
> > > 
> > > Oh, and assuming you found this in the XKB Protocol Specification
> > > then the answers to your question are in the same document, I
> > > think. For example groupInfo is explained on p32. Just search the
> > > document.  
> > 
> > Please, could you explain it on this example:
> > 
> > 01  14  00  00  = ktIndex   - what this means?
> > 02              = groupInfo - what info?
> > 04              = width     - of what?
> > 08  00          = 8 keysyms follow
> > 34  00  00  00  = "4"
> > 24  00  00  00  = "$"
> > 00  00  00  00  = NULL
> > 00  00  00  00  = NULL
> > 34  00  00  00  = "4"
> > 24  00  00  00  = "$"
> > AC  20  00  00  = "€" (euro sign)
> > AC  20  00  00  = "€" (euro sign)
> > 
> > What the constants 0x01, 0x14 (ktIndex), 0x02 (groupInfo) and 
> > 0x04 (width) means?  
> 
> From:
> https://www.x.org/releases/X11R7.7/doc/kbproto/xkbproto.html#XKB_Protocol_Requests
> """
> Key Symbol Map
> 
> The key symbol map for a key contains all of the information that a
> client needs to process events generated by that key. Each key symbol
> mapping reports:
> 
>     The number of groups of symbols bound to the key ( numGroups ).
>     The treatment of out-of-range groups ( groupInfo ).
>     The index of the key type to for each possible group (
> kt_index[MaxKbdGroups] ). The width of the widest type associated
> with the key ( groupsWidth ). The two-dimensional (numGroups ×
> groupsWidth) array of symbols bound to the key. """
> 
> XKB is a huge spec and you will need to support virtually *all* of it
> to get anywhere meaningful. Some terms that you don't know are
> specific terms used in the protocol, e.g. if you do not know what
> group "width" is that means you do not yet understand XKB well enough
> to implement a protocol parser.
> 
> And XKB is probably one of the most extensively documented protocols,
> both originally and in terms of follow ups by people who had to wrap
> their brains around it later.
> 
> Which is also why I said earlier: you can either become an XKB expert
> [1] or use libxkbcommon. XKB isn't *hard*, it's just complicated and
> a lot to implement.
> 
> Oh, and there's a PDF too https://www.x.org/docs/XKB/XKBproto.pdf in
> case you want to inflict that on your ebook reader.
> 
> Cheers,
>   Peter
> 
> [1] fwiw, the job market for those is rather small and you rarely get
> your face on TV during a crisis