ISO-10646 XFont encoding issue - c++

Question

I'm trying to use ISO-10646 fixed font in my X Window program. It has to support English, Russian and Greek letters but it doesn't. In xfontsel window all is OK but in my program only English displays correctly. Using something like g++ -fexec-charset=ISO-10646 ... or g++ -finput-charset=ISO-10646 ... wasn't helpful. How can I fix it?
Test app window screenshot:
xfontsel window screenshot:
Test app code:
#include <X11/StringDefs.h>
#include <X11/Xaw/Command.h>
int main(int argc, char **argv) {
Widget widget = XtInitialize(argv[0], "simple", NULL, 0, &argc, argv);
XtVaCreateManagedWidget(
"English Русский ελληνικά", labelWidgetClass, widget,
XtNfont, XLoadQueryFont(XtDisplay(widget),
"-Misc-Fixed-Medium-R-Normal--20-200-75-75-C-100-ISO10646-1"
), XtNwidth, 500, XtNheight, 100, NULL
);
XtRealizeWidget(widget);
XtMainLoop();
}

Answer 1

Your program uses UTF-8-encoded single byte strings, which is not what Xt/Xaw expects. -fexec-charset won't help any.
With pure Xlib (no toolkit) you would use Xutf8DrawString and friends, but Xt and Xaw have no provision for that.
Xaw theoretically supports 2-byte encodings of labels with XtNencoding set to XawTextEncodingChar2b, but I could never make it work with UTF-16.
XChar2b lbl[] = { {0x04, 0x40}, {0x04, 0x43},
{0x04, 0x41}, {0x04, 0x41},
{0x04, 0x3a}, {0x04, 0x38},
{0x04, 0x39}, {0, 0}};
XtVaCreateManagedWidget(
"w00t", labelWidgetClass, widget,
XtNfont, XLoadQueryFont(XtDisplay(widget),
"-Misc-Fixed-Medium-R-Normal--20-200-75-75-C-100-ISO10646-1"
), XtNwidth, 500, XtNheight, 100,
XtNencoding, XawTextEncodingChar2b,
XtNlabel, lbl,
NULL
);
This particular string works. I hope you can figure out how to produce an arbitrary label. However, a null byte at either high or low position terminates the string, so no English text can be displayed with this method.
Perhaps a copy of Xaw on my machine is not up to date. There is a patch that should make it work here but I don't know if it's applied on this copy and cannot be bothered to build a patched version from sources. Perhaps you shouldn't rely on it if you want to distribute your code dynamically linked, as not every machine will have an up-to-date Xaw library. This patch was made in 2014.
My advice would be not to rely on i18n abilities of Xaw. Use raw X11 with Xutf8DrawString, or a modern toolkit such as Qt or Gtk or FLTK or wxWidgets, which should all work with UTF-8 seamlessly. As the last resort, subclass Xaw widgets as needed and make them work with Xutf8DrawString.
Update I have checked the source from a Gentoo ebuild which ought to be up to date. The patch is not applied there, there is strlen everywhere, XChar2b is not working. A typical Xaw code fragment:
len = strlen(label);
...
if (len) {
if (w->label.encoding)
XDrawString16(XtDisplay(gw), XtWindow(gw), gc,
w->label.label_x, y, (XChar2b *)label, len / 2);
else
XDrawString(XtDisplay(gw), XtWindow(gw), gc,
w->label.label_x, y, label, len);
}
Clearly this cannot possibly have any hope of working correctly.