[SOLVED] UTF-8 input and using XGetICValues

Issue

I have found an example (accepted answer) of UTF-8 input but I wonder if that example is correct. The result of XGetICValues may be passed to XSelectInput:

unsigned long mask = 0;

if (!XGetICValues(ic, XNFilterEvents, &mask, NULL)) 
{
    XSelectInput(dpy, win, other_masks | mask);
}

Could you please explain what are implications of the above code ? Is it mandatory to get a correct UTF-8 input ? Should I also call XFilterEvent after executing the above code ?

Solution

Should I also call XFilterEvent after executing the above code ?

I suspect you should: for correct UTF-8 input handling, it's not only about getting the event mask and selecting the input events, but also potentially filtering these events to properly handle multibyte or special input sequences.

The XFilterEvent should be utilized within the event loop. It will help in managing the input method to interpret multibyte or special key sequences correctly.
As mentioned in "XLIB Programming Manual / Filtering Events", it is called right after XNextEvent().

#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/Xresource.h>
#include <X11/Xlocale.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
    
int main(int argc, char ** argv)
{
    // Your initialization code
    
    while(1) {
        XNextEvent(dpy, &ev);
        if (XFilterEvent(&ev, win))  // Filter the event through the input method
            continue;
        switch(ev.type){
        case MappingNotify:
            XRefreshKeyboardMapping(&ev.xmapping);
            break;
        case KeyPress:
            {
                int count = 0;
                KeySym keysym = 0;
                char buf[20];
                Status status = 0;
                count = Xutf8LookupString(ic, (XKeyPressedEvent*)&ev, buf, 20, &keysym, &status);
    
                printf("count: %d\n", count);
                if (status == XBufferOverflow)
                    printf("BufferOverflow\n");
    
                if (count)
                    printf("buffer: %.*s\n", count, buf);
 
                if (status == XLookupKeySym || status == XLookupBoth) {
                    printf("status: %d\n", status);
                }
                printf("pressed KEY: %d\n", (int)keysym);
            }
            break;
        case KeyRelease:
            // Rest of your code for other cases
        }
        fflush(stdout);
    }
}

If XFilterEvent returns True, indicating that the event has been filtered and handled by the input method, the continue statement is executed to skip the rest of the loop and process the next event.

+--------------------+    XNFilterEvents        +--------------+
| Input Context (IC) |------------------------->| Event Mask   |
+--------------------+                          +--------------+
           |                                           |
      XGetICValues                               Retrieved Mask
           |                                           |
           V                                           V
+--------------------+    other_masks | mask    +--------------+
| XSelectInput       |------------------------->| Event Input  |
+--------------------+                          +--------------+
           |                                           |
           |                                    +--------------+
           |                                    | X Event      |
           |                                    +--------------+
           |                                           |
           V                                           V
+--------------------+    XFilterEvent          +--------------+
| Event Loop         |------------------------->| Event Filter |
+--------------------+    (optional)            +--------------+

• The Input Context (IC) is queried to get the event mask which is needed for XSelectInput to know which events to listen for.
• XSelectInput is called with a combination of other masks and the retrieved mask to specify the events that should be reported for the specified window.
• In the event loop, XFilterEvent is called to filter the event queue for the relevant input events, particularly useful when dealing with multibyte or special input sequences. This step is marked as optional, since it's based on the requirement to handle special input sequences.

Answered By - VonC

Answer Checked By - Robin (WPSolving Admin)