Fly Catch

We can only make a small change to the fly catch game for now, but it is a start. Have a go at this yourself. Our version is shown below.

#include "splashkit.h"

const string GAME_TIMER = "GameTimer";

const int SCREEN_WIDTH = 800;
const int SCREEN_HEIGHT = 600;
const int SPIDER_RADIUS = 25;
const int SPIDER_SPEED = 3;

const int FLY_RADIUS = 10;

/**
 * The fly can appear and escape (disappear), but is otherwise
 * located on the screen at a certain point.
 *
 * @field appeared  indicates if the fly is shown
 * @field x its distance from the left of the window (to the center)
 * @field y its distance from the top of the window (to the center)
 * @field appear_at_time  the time when the fly will appear
 * @field escape_at_time  the time when the fly will escape
*/
typedef struct
{
  bool appeared;
  double x;
  double y;

  long appear_at_time;
  long escape_at_time;
} fly_data;

/**
 * The spider has a location on the screen.
 *
 * @field x the distance from the left side of the window
 * @field y the distance from the top of the window
*/
typedef struct
{
  double x;
  double y;
} spider_data;

/**
 * The game involves a spider and a fly. The player is
 * controlling the spider and the fly is trying to escape.
 *
 * @field spider  the data about the spider
 * @field fly     the data for the fly
*/
typedef struct
{
  spider_data spider;
  fly_data    fly;
} game_data;

/**
 * Draw the spider on the screen
 *
 * @param spider  the spider's data
*/
void draw_spider(spider_data spider)
{
  fill_circle(color_black(), spider.x, spider.y, SPIDER_RADIUS);
}

/**
 * Draw the fly if it has appeared
 *
 * @field fly the fly data
*/
void draw_fly(fly_data fly)
{
  // Exit if the fly has not appeared
  if (!fly.appeared)
  {
    return;
  }

  // Draw the fly
  fill_circle(color_dark_green(), fly.x, fly.y, FLY_RADIUS);
}

/**
 * Draw the spider and the fly to the screen.
 *
 * @param game the game data
*/
void draw_game(game_data game)
{
  // Draw the game
  clear_screen(color_white());

  // Draw the spider
  draw_spider(game.spider);

  // Draw the fly
  draw_fly(game.fly);

  // Show it to  the user
  refresh_screen(60);
}

/**
 * Initialise a new spider and return it to the caller.
 * The spider will be in the center of the screen.
 *
 * @return an initialised spider
*/
spider_data new_spider()
{
  spider_data result;

  // Set the spider in the center of the screen
  result.x = SCREEN_WIDTH / 2;
  result.y = SCREEN_HEIGHT / 2;

  return result;
}

/**
 * Initialise and return new fly data. This will not have appeared,
 * but will be at a random position, and will appear within 1
 * to 3 seconds.
 *
 * @return the newly initialised fly
*/
fly_data new_fly()
{
  fly_data result;

  result.x = rnd(SCREEN_WIDTH);
  result.y = rnd(SCREEN_HEIGHT);

  result.appeared = false;

  result.appear_at_time = 1000 + rnd(2000);
  result.escape_at_time = 0;

  return result;
}

/**
 * Indicates if it is time for the fly to appear.
 *
 * @param fly the fly to check
 * @param current_time  the current time
*/
bool time_to_appear(fly_data fly, long current_time)
{
  return !fly.appeared && current_time > fly.appear_at_time;
}

/**
 * Indicates if it is time for the fly to escape.
 *
 * @param fly the fly to check
 * @param current_time  the current time
*/
bool time_to_escape(fly_data fly, long current_time)
{
  return fly.appeared && current_time > fly.escape_at_time;
}

/**
 * Tests if the spider has caught the fly. This is calculated
 * by checking if the spider and fly circles intersect.
 *
 * @param spider  the spider data
 * @param fly     the fly data
 * @return true if the spider has caught the fly.
*/
bool spider_caught_fly(spider_data spider, fly_data fly)
{
  return fly.appeared && circles_intersect(
    spider.x, spider.y, SPIDER_RADIUS,
    fly.x, fly.y, FLY_RADIUS);
}

int main()
{
  game_data game;

  game.spider = new_spider();
  game.fly = new_fly();

  open_window("Fly Catch", SCREEN_WIDTH, SCREEN_HEIGHT);

  create_timer(GAME_TIMER);
  start_timer(GAME_TIMER);

  // The event loop
  while (!quit_requested())
  {
    // Handle Input
    if (key_down(RIGHT_KEY) && game.spider.x + SPIDER_RADIUS < SCREEN_WIDTH)
    {
      game.spider.x += SPIDER_SPEED;
    }
    if (key_down(LEFT_KEY) && game.spider.x - SPIDER_RADIUS > 0)
    {
      game.spider.x -= SPIDER_SPEED;
    }

    if (key_down(DOWN_KEY) && game.spider.y + SPIDER_RADIUS < SCREEN_HEIGHT)
    {
      game.spider.y += SPIDER_SPEED;
    }
    if (key_down(UP_KEY) && game.spider.y - SPIDER_RADIUS > 0)
    {
      game.spider.y -= SPIDER_SPEED;
    }

    // Update the Game
    // Check if the fly should appear
    if (time_to_appear(game.fly, timer_ticks(GAME_TIMER)))
    {
      // Make the fly appear
      game.fly.appeared = true;

      // Give it a new random position
      game.fly.x = rnd(SCREEN_WIDTH);
      game.fly.y = rnd(SCREEN_HEIGHT);

      // Set its escape time
      game.fly.escape_at_time = timer_ticks(GAME_TIMER) + 2000 + rnd(5000);
    }
    else if (time_to_escape(game.fly, timer_ticks(GAME_TIMER)))
    {
      game.fly.appeared = false;
      game.fly.appear_at_time = timer_ticks(GAME_TIMER) + 1000 + rnd(2000);
    }

    if ( spider_caught_fly(game.spider, game.fly) )
    {
      game.fly.appeared = false;
      game.fly.appear_at_time = timer_ticks(GAME_TIMER) + 1000 + rnd(2000);
    }

    draw_game(game);

    // Get any new user interactions
    process_events();
  }

  return 0;
}