Names of keyboard codes

Jacek_Podkanski · February 16, 2025, 4:40pm

I am trying to translate pressed key into name of the key.
This is the source of my information:

Has somebody done it before? Ifnot, how can I use ctypes to import the data from the file? Part of the problem is the fact that GDK library for GTK4 is not available on Ubuntu like systems.

I vowed to give up on OCaml, but I have discovered solution to my problems, so I wonder how far I will progress this time.

github.com/bigos/gtk_minimal

bin/main.ml

main

(*
   Select both lines and do C-c C-r to paste them into REPL
    #cd "/home/jacek/Programming/OCaml/gtk_minimal/";;
    #use ".ocamlinit";;
  You can do C-c C-b to evaluate the whole buffer or select the following line
  and doing C-c C-r
    # use "./bin/main.ml";;
*)

open Ctypes
open Foreign

let libgtk = Dl.dlopen ~flags:Dl.[RTLD_NOW] ~filename:"libgtk-4.so"

let libgio = Dl.dlopen ~flags:Dl.[RTLD_NOW] ~filename:"libgio-2.0.so"

let libgobject = Dl.dlopen ~flags:Dl.[RTLD_NOW] ~filename:"libgobject-2.0.so"

let libcairo = Dl.dlopen ~flags:Dl.[RTLD_NOW] ~filename:"libcairo.so.2"

This file has been truncated. show original

Jacek_Podkanski · February 17, 2025, 1:52am

I’m embarrassed by my solution. It will read and process the file on every key press.

github.com/bigos/gtk_minimal

bin/main.ml

50898c6d1


      
            |> List.filter (fun s -> String.starts_with ~prefix:"#def" s)
            |> List.map (fun s -> String.split_on_char (Char.chr 32) s)
            |> List.map (fun sl -> List.tl sl)
          
          let find_code str =
            let lc = list_of_codes in
            List.filter (fun pl -> String.equal str (List.nth pl 1)) lc
          
          (* finish the following *)
          let key_pressed_func _w kc kv s _z =
            let kc_name =
              try find_code (Printf.sprintf "0x%x" kc) |> List.hd |> List.hd
              with _ ->
                if kc <= 255 then String.make 1 (Char.chr kc) else "unexpected situation"
            in
            (* need to finfd how to handle exceptions *)
            Printf.printf "key %x %d %d %d  %s\n" kc kc kv s kc_name ;
            Printf.printf "%!" ;
            ()
          
          let window_events _app window =

But I need to have a break from OCaml until next weekend.

sanette · February 17, 2025, 8:23am

if the codes are contiguous, I suggest first transforming your list into a string array, then accessing like key_name.(i-offset) will be much faster

otherwise you may also convert you list into a Map, it will also be quite faster

yallop · February 20, 2025, 8:19am

You can use the constant function for retrieving the values of constants. There are a few steps, though:

Create a constant binding for every symbols that you want to bind, e.g.

      let _GDK_KEY_VoidSymbol = constant "GDK_KEY_VoidSymbol" int64_t

Add them to a parameterized module Bindings:

module Bindings(C: Cstubs_structs.TYPE) = struct
   open C
   let _GDK_KEY_VoidSymbol = constant "GDK_KEY_VoidSymbol" int64_t
   let _GDK_KEY_BackSpace = constant "GDK_KEY_BackSpace" int64_t
   [...]
end

Pass the Bindings module to Cstubs_structs.write_c:
```
Cstubs_structs.write_c Format.std_formatter (module Bindings)
```
which will generate a C program that builds an OCaml module with an entry for each of the symbols you bound with constant.

It’s a slightly complex workflow, since (a) it needs to handle lots of other cases (b) it generates efficient code that allows the extracted constants to be inlined, and (c) it provides some degree of safety. For a simple case you might find it easier just to extract the constants and build the module directly (i.e. without using ctypes).

Jacek_Podkanski · February 20, 2025, 9:28am

I also thought about it.

Jacek_Podkanski · February 20, 2025, 9:33am

Using constants is a very interesting approach. For the time being, when I have time to come back to my project, I will try to use Hash. But it’s nice to see the ability to make it even faster.

Thank you very much for advice.

Topic		Replies	Views
G_object_unref and ctypes Learning	2	616	May 29, 2022
Writing ctypes bindings to system shared libraries for bytecode targets via the dune ctypes stanza Ecosystem dune	11	475	January 11, 2024
[ANN] living 0.1.0 Ecosystem ffi , ctypes	0	226	July 13, 2024
[ANN] ctypes 0.21.1, now with dune support Community announce , ffi , dune	0	404	July 24, 2023
Running in to an issue when using CTypes Learning c	1	416	October 14, 2023

Names of keyboard codes

Related topics