Pebble watchface background image example code

pebble_set_background.c

static void set_background_gem(int color) {
  APP_LOG(APP_LOG_LEVEL_DEBUG, "Updating background gem");
  if (s_bitmap) gbitmap_destroy(s_bitmap);
  switch(color) {
    case 0:
      s_bitmap = gbitmap_create_with_resource(RESOURCE_ID_DIAMOND);
      break;
    case 1:
      s_bitmap = gbitmap_create_with_resource(RESOURCE_ID_DIAMONDAQUA);
      break;
    // (...)
    default:
      s_bitmap = gbitmap_create_with_resource(RESOURCE_ID_DIAMOND);
  }
  bitmap_layer_set_bitmap(s_bitmap_layer, s_bitmap);
}