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

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 
#include 
#include 
#include 
#include 

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;
}