Basic countdown app for the Pebble smartwatch.

simple-countdown.c

#include "pebble_os.h"
#include "pebble_app.h"
#include "pebble_fonts.h"

#define MY_UUID { 0xD6, 0xEB, 0x90, 0xCA, 0x3F, 0x77, 0x43, 0xB7, 0xAD, 0x5A, 0x79, 0xDE, 0x29, 0xF8, 0x68, 0x7C }

PBL_APP_INFO(MY_UUID, "Simple Countdown", "Matthew Tole", 1, 0, DEFAULT_MENU_ICON, APP_INFO_STANDARD_APP);

Window window;
TextLayer text_layer;
AppTimerHandle timer_handle;

#define COOKIE_COUNTDOWN 1

int time_remaining = 5 * 60;

/**
 * Set a timer event for 1 second from now.
 */
void set_timer(AppContextRef ctx) {
  timer_handle = app_timer_send_event(ctx, 1000, COOKIE_COUNTDOWN);
}

/**
 * Update the text layer with the time remaining.
 */
void update_countdown_text() {
  static char countdown_text[] = "00:00";
  snprintf(countdown_text, sizeof(countdown_text), "%02d:%02d", (time_remaining / 60), (time_remaining % 60));
  text_layer_set_text(&text_layer, countdown_text);
}

/**
 * Event handler for all timer events.
 * If the timer cookie is the countdown, decrement the time remaining, update
 * the text and set the timer again.
 */
void handle_timer(AppContextRef ctx, AppTimerHandle handle, uint32_t cookie) {
  if (cookie == COOKIE_COUNTDOWN) {
    time_remaining -= 1;
    update_countdown_text();
    if (time_remaining > 0) {
      set_timer(ctx);
    }
  }
}

/**
 * Handler for the app init event.
 * Create the window and text layer, and then start the countdown.
 */
void handle_init(AppContextRef ctx) {
  window_init(&window, "Countdown Window");
  window_stack_push(&window, true);

  text_layer_init(&text_layer, GRect(0, 46, 144, 60));
  text_layer_set_text_color(&text_layer, GColorBlack);
  text_layer_set_background_color(&text_layer, GColorClear);
  text_layer_set_font(&text_layer, fonts_get_system_font(FONT_KEY_BITHAM_42_BOLD));
  text_layer_set_text_alignment(&text_layer, GTextAlignmentCenter);
  layer_add_child(&window.layer, &text_layer.layer);

  update_countdown_text();
  set_timer(ctx);
}

/**
 * Pebble app entry point.
 */
void pbl_main(void *params) {
  PebbleAppHandlers handlers = {
    .init_handler = &handle_init,
    .timer_handler = &handle_timer
  };
  app_event_loop(params, &handlers);
}