Enhance libi3 and use it in i3bar.

Abstracted draw_text and predict_text_width into libi3. Use
predict_text_width from libi3 in i3 too. This required tracking
xcb_connection in a xcb_connection_t *conn variable that libi3
expects to be available in i3bar.

src/cfgparse.y

@@ -1546,6 +1546,7 @@ font:
     TOKFONT STR
     {
         config.font = load_font($2, true);
+        set_font(&config.font);
         printf("font %s\n", $2);
         FREE(font_pattern);
         font_pattern = $2;

src/config.c

@@ -371,6 +371,7 @@ void load_configuration(xcb_connection_t *conn, const char *override_configpath,
     if (config.font.id == 0) {
         ELOG("You did not specify required configuration option \"font\"\n");
         config.font = load_font("fixed", true);
+        set_font(&config.font);
     }
 
 #if 0

src/sighandler.c

@@ -152,7 +152,7 @@ void handle_signal(int sig, siginfo_t *info, void *data) {
     /* calculate width for longest text */
     int text_len = strlen(crash_text[crash_text_longest]);
     xcb_char2b_t *longest_text = convert_utf8_to_ucs2(crash_text[crash_text_longest], &text_len);
-    int font_width = predict_text_width(longest_text, text_len);
+    int font_width = predict_text_width((char *)longest_text, text_len, true);
     int width = font_width + 20;
 
     /* Open a popup window on each virtual screen */

src/xcb.c

@@ -130,32 +130,6 @@ void xcb_raise_window(xcb_connection_t *conn, xcb_window_t window) {
     xcb_configure_window(conn, window, XCB_CONFIG_WINDOW_STACK_MODE, values);
 }
 
-/*
- * Query the width of the given text (16-bit characters, UCS) with given real
- * length (amount of glyphs) using the given font.
- *
- */
-int predict_text_width(const xcb_char2b_t *text, int length) {
-    xcb_query_text_extents_cookie_t cookie;
-    xcb_query_text_extents_reply_t *reply;
-    xcb_generic_error_t *error;
-    int width;
-
-    cookie = xcb_query_text_extents(conn, config.font.id, length, text);
-    if ((reply = xcb_query_text_extents_reply(conn, cookie, &error)) == NULL) {
-        ELOG("Could not get text extents (X error code %d)\n",
-             error->error_code);
-        /* We return the rather safe guess of 7 pixels, because a
-         * rendering error is better than a crash. Plus, the user will
-         * see the error in his log. */
-        return 7;
-    }
-
-    width = reply->overall_width;
-    free(reply);
-    return width;
-}
-
 /*
  * Configures the given window to have the size/position specified by given rect
  *