Why can't I display emoji on Pebble using Symbola font?

Question

I added the Symbola font to my watch app, and tried to display some emoji on the Pebble, but alas, no dice.

Here's the relevant vars and functions in my code… be gentle, I'm kind of a C n00b.

Is this even the proper way to format unicode for a C string? I added the colons just as separators.

static char emoji_chars[]=":\xF0\x9F\x98\x81:\xF0\x9F\x98\x93:";

void handle_init(AppContextRef ctx) {
  (void)ctx;

  window_init(&window, "Window Name");
  window_stack_push(&window, true /* Animated */);
  text_layer_init(&emoji_layer, GRect(30, 30, 150, 50));
  text_layer_set_background_color(&emoji_layer, GColorWhite);
  text_layer_set_text_color(&emoji_layer, GColorBlack);
  text_layer_set_font(&emoji_layer, fonts_load_custom_font(resource_get_handle(RESOURCE_ID_SYMBOLA_24)));
  text_layer_set_text(&emoji_layer, emoji_chars);
  layer_add_child(&window.layer, &emoji_layer.layer);
}

void pbl_main(void *params) {
  resource_init_current_app(&APP_RESOURCES);
  PebbleAppHandlers handlers = {
    .init_handler = &handle_init
  };
  app_event_loop(params, &handlers);
}

Answer 1

The documentation says on the argument of text_layer_set_text

The new text to set onto the TextLayer. This must be a null-terminated and valid UTF-8 string!

(note the exclamation point). "Unicode" is not a valid C string encoding, but "UTF-8" is. Inserting your icons' Unicode values as UTF-8 characters should work.

Edit

Hold on -- you already encoded the character U+1F601 as UTF-8. And it is a valid character in your font, according to http://users.teilar.gr/~g1951d/Symbola.pdf.

Answer 2

Have you in the font resource manifest specified those emoji characters in the characterRegex?

I also see that there is a patch for fontgen.py to include unicode here That may assist you.

https://github.com/fisakov/pebble-sdk-characterRegex