Xkb: How to convert a keycode to keysym

Question

I am simply trying to take a KeyCode and a modifier mask and convert it to a KeySym using the Xkb extension. I cant seem to figure out why this doesn\'t work. Its obvious

Answer 1

From the man page of XKeycodeToKeysym:

   The XKeycodeToKeysym function uses internal Xlib tables and returns the
   KeySym defined for the specified KeyCode and the element of the KeyCode
   vector.  If no symbol is defined, XKeycodeToKeysym returns NoSymbol.
   XKeycodeToKeysym predates the XKB extension. If you want to lookup a
   KeySym while using XKB you have to use XkbKeycodeToKeysym.

I don't see that in your sample code.

Read the full manpage for more info.

Answer 2

I was finally able to figure it out after a lot of trial and error. XKeycodeToKeysym is apparently broken and the index value calculations are not defined for extended indexes.

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <X11/X.h>
#include <X11/XKBlib.h>

KeySym KeyCodeToKeySym(Display * display, KeyCode keycode, unsigned int event_mask) {
    KeySym keysym = NoSymbol;

    //Get the map
    XkbDescPtr keyboard_map = XkbGetMap(display, XkbAllClientInfoMask, XkbUseCoreKbd);
    if (keyboard_map) {
        //What is diff between XkbKeyGroupInfo and XkbKeyNumGroups?
        unsigned char info = XkbKeyGroupInfo(keyboard_map, keycode);
        unsigned int num_groups = XkbKeyNumGroups(keyboard_map, keycode);

        //Get the group
        unsigned int group = 0x00;
        switch (XkbOutOfRangeGroupAction(info)) {
            case XkbRedirectIntoRange:
                /* If the RedirectIntoRange flag is set, the four least significant
                 * bits of the groups wrap control specify the index of a group to
                 * which all illegal groups correspond. If the specified group is
                 * also out of range, all illegal groups map to Group1.
                 */
                group = XkbOutOfRangeGroupInfo(info);
                if (group >= num_groups) {
                    group = 0;
                }
            break;

            case XkbClampIntoRange:
                /* If the ClampIntoRange flag is set, out-of-range groups correspond
                 * to the nearest legal group. Effective groups larger than the
                 * highest supported group are mapped to the highest supported group;
                 * effective groups less than Group1 are mapped to Group1 . For
                 * example, a key with two groups of symbols uses Group2 type and
                 * symbols if the global effective group is either Group3 or Group4.
                 */
                group = num_groups - 1;
            break;

            case XkbWrapIntoRange:
                /* If neither flag is set, group is wrapped into range using integer
                 * modulus. For example, a key with two groups of symbols for which
                 * groups wrap uses Group1 symbols if the global effective group is
                 * Group3 or Group2 symbols if the global effective group is Group4.
                 */
            default:
                if (num_groups != 0) {
                    group %= num_groups;
                }
            break;
        }

        XkbKeyTypePtr key_type = XkbKeyKeyType(keyboard_map, keycode, group);
        unsigned int active_mods = event_mask & key_type->mods.mask;

        int i, level = 0;
        for (i = 0; i < key_type->map_count; i++) {
            if (key_type->map[i].active && key_type->map[i].mods.mask == active_mods) {
                level = key_type->map[i].level;
            }
        }

        keysym = XkbKeySymEntry(keyboard_map, keycode, level, group);
        XkbFreeClientMap(keyboard_map, XkbAllClientInfoMask, true);
    }

    return keysym;
}

int main(int argc, const char * argv[]) {
    Display * display;

    //Try to attach to the default X11 display.
    display = XOpenDisplay(NULL);
    if(display == NULL) {
        printf("Error: Could not open display!\n");
        return EXIT_FAILURE;
    }

    KeyCode keycode = 56; // b
    unsigned int event_mask = ShiftMask | LockMask;
    KeySym keysym = KeyCodeToKeySym(display, keycode, event_mask);

    printf("KeySym: %s\n", XKeysymToString(keysym));

    //Close the connection to the selected X11 display.
    XCloseDisplay(display);

    return EXIT_SUCCESS;
}