X11: Make glfwGetKeyName return UTF-8 strings

Fixes #981.
Closes #983.

src/x11_window.c

@@ -876,6 +876,36 @@ static void releaseMonitor(_GLFWwindow* window)
     }
 }
 
+// Encode a Unicode code point to a UTF-8 stream
+// Based on cutef8 by Jeff Bezanson (Public Domain)
+//
+static size_t encodeUTF8(char *dest, uint32_t ch)
+{
+    if (ch < 0x80) {
+        dest[0] = (char)ch;
+        return 1;
+    }
+    if (ch < 0x800) {
+        dest[0] = (ch>>6) | 0xC0;
+        dest[1] = (ch & 0x3F) | 0x80;
+        return 2;
+    }
+    if (ch < 0x10000) {
+        dest[0] = (ch>>12) | 0xE0;
+        dest[1] = ((ch>>6) & 0x3F) | 0x80;
+        dest[2] = (ch & 0x3F) | 0x80;
+        return 3;
+    }
+    if (ch < 0x110000) {
+        dest[0] = (ch>>18) | 0xF0;
+        dest[1] = ((ch>>12) & 0x3F) | 0x80;
+        dest[2] = ((ch>>6) & 0x3F) | 0x80;
+        dest[3] = (ch & 0x3F) | 0x80;
+        return 4;
+    }
+    return 0;
+}
+
 // Decode a Unicode code point from a UTF-8 stream
 // Based on cutef8 by Jeff Bezanson (Public Domain)
 //
@@ -2446,7 +2476,8 @@ void _glfwPlatformSetCursorMode(_GLFWwindow* window, int mode)
 const char* _glfwPlatformGetKeyName(int key, int scancode)
 {
     KeySym keysym;
-    int extra;
+    long ch;
+    size_t sz;
 
     if (!_glfw.x11.xkb.available)
         return NULL;
@@ -2459,14 +2490,16 @@ const char* _glfwPlatformGetKeyName(int key, int scancode)
 
     keysym = XkbKeycodeToKeysym(_glfw.x11.display, scancode, 0, 0);
     if (keysym == NoSymbol)
-      return NULL;
+        return NULL;
 
-    XkbTranslateKeySym(_glfw.x11.display, &keysym, 0,
-                       _glfw.x11.keyName, sizeof(_glfw.x11.keyName),
-                       &extra);
+    ch = _glfwKeySym2Unicode(keysym);
+    if (ch == -1)
+        return NULL;
 
-    if (!strlen(_glfw.x11.keyName))
+    sz = encodeUTF8(_glfw.x11.keyName, (uint32_t)ch);
+    if (sz == 0)
         return NULL;
+    _glfw.x11.keyName[sz] = '\0';
 
     return _glfw.x11.keyName;
 }

src/xkb_unicode.c

@@ -826,6 +826,59 @@ static const struct codepair {
   { 0x13bd, 0x0153 },
   { 0x13be, 0x0178 },
   { 0x20ac, 0x20ac },
+  // dead keys
+  { 0xfe50,    '`' },
+  { 0xfe51, 0x00b4 },
+  { 0xfe52,    '^' },
+  { 0xfe53,    '~' },
+  { 0xfe54, 0x00af },
+  { 0xfe55, 0x02d8 },
+  { 0xfe56, 0x02d9 },
+  { 0xfe57, 0x00a8 },
+  { 0xfe58, 0x02da },
+  { 0xfe59, 0x02dd },
+  { 0xfe5a, 0x02c7 },
+  { 0xfe5b, 0x00b8 },
+  { 0xfe5c, 0x02db },
+  { 0xfe5d, 0x037a },
+  { 0xfe5e, 0x309b },
+  { 0xfe5f, 0x309c },
+  // { 0xfe60, 0x0323 }, // XK_dead_belowdot
+  // { 0xfe61, 0x0309 }, // XK_dead_hook
+  // { 0xfe62, 0x031b }, // XK_dead_horn
+  { 0xfe63,    '/' },
+  { 0xfe64, 0x02bc },
+  { 0xfe65, 0x02bd },
+  { 0xfe66, 0x02f5 },
+  { 0xfe67, 0x02f3 },
+  { 0xfe68, 0x02cd },
+  { 0xfe69, 0xa788 },
+  { 0xfe6a, 0x02f7 },
+  // { 0xfe6b, 0x032e }, // XK_dead_belowbreve
+  // { 0xfe6c, 0x0324 }, // XK_dead_belowdiaeresis
+  // { 0xfe6d, 0x0311 }, // XK_dead_invertedbreve
+  { 0xfe6e,    ',' },
+  { 0xfe6f, 0x00a4 },
+  // dead vowels for universal syllable entry
+  { 0xfe80,    'a' }, // XK_dead_a
+  { 0xfe81,    'A' }, // XK_dead_A
+  { 0xfe82,    'e' }, // XK_dead_e
+  { 0xfe83,    'E' }, // XK_dead_E
+  { 0xfe84,    'i' }, // XK_dead_i
+  { 0xfe85,    'I' }, // XK_dead_I
+  { 0xfe86,    'o' }, // XK_dead_o
+  { 0xfe87,    'O' }, // XK_dead_O
+  { 0xfe88,    'u' }, // XK_dead_u
+  { 0xfe89,    'U' }, // XK_dead_U
+  { 0xfe8a, 0x0259 },
+  { 0xfe8b, 0x018f },
+  // other
+  { 0xfe8c, 0x00b5 },
+  // extra dead elements for German T3 layout
+  { 0xfe90,    '_' },
+  { 0xfe91, 0x02c8 },
+  { 0xfe92, 0x02cc },
+  // { 0xfe93,     0x0338 }, // XK_dead_longsolidusoverlay
   // Numeric keypad with numlock on
   { 0xff80 /*XKB_KEY_KP_Space*/,     ' ' },
   { 0xffbd /*XKB_KEY_KP_Equal*/,     '=' },