Problems in Typing Vietnamese in Gtk application

[Gaurav Jain <gaurav anywhere gmail com>]

Hello!

I have a small program (code at the end of this mail), in which I'm trying
to achieve the following:
- Type Vietnamese characters, such that the key-presses are processed by a
GtkLayout, and the actual text is shown on a GtkLabel. I cannot directly use
a GtkEntry or a GtkTextView, (which both work fine, if I were allowed to use
them)

Now whenever a vowel's accent is typed subsequent to the vowel (e.g., if I
type 'ee', this should become 'ê'), the key-press-callback returns 'e' both
times. The GtkIMContext's commit-callback returns "e" first time, and "ê" on
the second time. The problem is that I'm unable to find out a way to realize
that the second "ê" corresponds to the first "e", and I'm supposed to erase
the "e" from the GtkLabel, and replace it with a "ê". There are callbacks
called "retrieve_surrounding" and "delete_surrounding" in the GtkIMContext
which sound like they may help me out (if I get the opportunity to provide
the context to the IME), but they are actually NEVER called!

Could somebody help me understand if any of the following are possible, and
how:
1) Somehow get the IME to invoke the "retrieve_surrounding" and
"delete_surrounding" callbacks, so that I can provide the context to the
IME, and delete the already entered characters if I'm typing a new accented
version of a character (like the "ê").
2) Somehow be able to calculate that the character 'ê' is an accented
version of the character 'e' (in general for any accented character in
vietnamese).

If any of the above is possible, I would be able to resolve my problem.
Maybe there's a third way to do it too. I'm using Red Hat EL Workstation 4.0,
and the IME is called X-Unikey (http://unikey.sourceforge.net/linux.php)

Sorry about the long mail, but since the problem is a bit deep, I needed to
give some explanation. Any help in this regard would be highly
appreciated!!!

Thanks in advance,
Gaurav

----- code follows -----
#include <stdio.h>
#include <stdlib.h>
#include <gtk/gtk.h>
#include <gdk/gdk.h>

GtkWidget *layout;
GtkIMContext *imContext = NULL;
GtkWidget *label;
gboolean keypresscallback(GtkWidget *widget, GdkEvent *event, gpointer data)
{
//printf("keypresscallback, event->key = %d\n", event->key);
//const char *full_text = gtk_label_get_label(GTK_LABEL(label));
//int length = g_utf8_strlen(full_text, -1);
//gtk_im_context_set_surrounding(imContext, full_text, length, length);
if (gtk_im_context_filter_keypress(imContext, &(event->key)))
{
return TRUE;
}

return FALSE;
}

void commit_cb(GtkIMContext *context, const gchar *str, gpointer data)
{
GtkWidget *entry = (GtkWidget *)data;
printf("commit_cb [%s], %d\n", str, str[0]);
//gtk_im_context_set_surrounding(context, full_text, length, length);
const char *old_text = gtk_label_get_label(GTK_LABEL(label));
int length = g_utf8_strlen(old_text, -1);
char *full_text = (char *)malloc(length + 1 + g_utf8_strlen(str, -1));
strcpy(full_text, old_text);
strcat(full_text, str);
gtk_label_set_text(GTK_LABEL(label), full_text);
free(full_text);
}

void preedit_start_cb(GtkIMContext *imContext, gpointer clientData)
{
printf("preedit_start_cb\n");
}

void preedit_changed_cb(GtkIMContext *imContext, gpointer clientData)
{
printf("preedit_changed_cb\n");
}

void preedit_end_cb(GtkIMContext *imContext, gpointer clientData)
{
printf("preedit_end_cb\n");
}

gboolean retrieve_surrounding_cb(GtkIMContext *context, gpointer data)
{
printf("retrieve_surrounding_cb\n");
return FALSE;
}

gboolean delete_surrounding_cb(GtkIMContext *context, gint offset, gint
n_chars, gpointer data)
{
printf("delete_surrounding_cb\n");
return FALSE;
}

int main( int argc, char *argv[] )
{
GtkWidget *window;
GtkWidget *vbox, *hbox;

gtk_init (&argc, &argv);

/* create a new window */
window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
gtk_widget_set_size_request (GTK_WIDGET (window), 200, 100);
gtk_window_set_title (GTK_WINDOW (window), "Typing Vietnamese");
g_signal_connect (G_OBJECT (window), "destroy", G_CALLBACK (gtk_main_quit),
NULL);
g_signal_connect_swapped (G_OBJECT (window), "delete_event", G_CALLBACK
(gtk_widget_destroy), G_OBJECT (window));

vbox = gtk_vbox_new (FALSE, 0);
gtk_container_add (GTK_CONTAINER (window), vbox);
gtk_widget_show (vbox);

/* add layout */
GdkColor layout_color = {0, 0xFFFF, 0x0000, 0x0000};
layout = gtk_layout_new(NULL, NULL);
GTK_WIDGET_SET_FLAGS(layout, GTK_CAN_FOCUS);
gtk_widget_modify_bg(layout, GTK_STATE_NORMAL, &layout_color);
gtk_box_pack_start (GTK_BOX (vbox), layout, TRUE, TRUE, 0);
gtk_widget_show (layout);

/* add label */
label = gtk_label_new("");
gtk_box_pack_start (GTK_BOX (vbox), label, TRUE, TRUE, 0);
gtk_widget_show (label);

hbox = gtk_hbox_new (FALSE, 0);
gtk_container_add (GTK_CONTAINER (vbox), hbox);
gtk_widget_show (hbox);

gtk_widget_show (window);

/* add events to the layout */
GdkWindow *gdkWin = GTK_LAYOUT(layout)->bin_window;
gint eveMask = gdk_window_get_events(gdkWin);
eveMask |= GDK_ALL_EVENTS_MASK;
gdk_window_set_events(gdkWin, (GdkEventMask)eveMask);
gtk_widget_add_events(layout, GDK_ALL_EVENTS_MASK);
g_signal_connect (G_OBJECT (layout), "key-press-event", G_CALLBACK
(keypresscallback), NULL);

/* create the IM context */
imContext = gtk_im_multicontext_new();
g_signal_connect(G_OBJECT(imContext), "commit", G_CALLBACK(commit_cb),
(gpointer)label);
g_signal_connect(G_OBJECT(imContext), "preedit_changed",
G_CALLBACK(preedit_changed_cb), (gpointer)label);
g_signal_connect(G_OBJECT(imContext), "preedit_start",
G_CALLBACK(preedit_start_cb), (gpointer)label);
g_signal_connect(G_OBJECT(imContext), "preedit_end",
G_CALLBACK(preedit_end_cb), (gpointer)label);
g_signal_connect (G_OBJECT (imContext), "retrieve_surrounding", G_CALLBACK
(retrieve_surrounding_cb), label);
g_signal_connect (G_OBJECT (imContext), "delete_surrounding", G_CALLBACK
(delete_surrounding_cb), label);
GdkWindow *im_context_window = (GTK_IS_LAYOUT(layout) ?
(GTK_LAYOUT(layout))->bin_window: layout->window);
gtk_im_context_set_client_window (imContext, im_context_window);

gtk_main();

return 0;
}