MonoGame.Samples/NetworkStateManagement/Core/Screens/LoadingScreen.cs

//-----------------------------------------------------------------------------
// LoadingScreen.cs
//
// Microsoft XNA Community Game Platform
// Copyright (C) Microsoft Corporation. All rights reserved.
//-----------------------------------------------------------------------------

using System;
using System.Threading;
using System.Diagnostics;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Net;


namespace NetworkStateManagement
{
	/// <summary>
	/// The loading screen coordinates transitions between the menu system and the
	/// game itself. Normally one screen will transition off at the same time as
	/// the next screen is transitioning on, but for larger transitions that can
	/// take a longer time to load their data, we want the menu system to be entirely
	/// gone before we start loading the game. This is done as follows:
	/// 
	/// - Tell all the existing screens to transition off.
	/// - Activate a loading screen, which will transition on at the same time.
	/// - The loading screen watches the state of the previous screens.
	/// - When it sees they have finished transitioning off, it activates the real
	///   next screen, which may take a long time to load its data. The loading
	///   screen will be the only thing displayed while this load is taking place.
	/// </summary>
	class LoadingScreen : GameScreen
	{

		bool loadingIsSlow;
		bool otherScreensAreGone;
		GameScreen[] screensToLoad;
		Thread backgroundThread;
		EventWaitHandle backgroundThreadExit;
		GraphicsDevice graphicsDevice;
		NetworkSession networkSession;
		IMessageDisplay messageDisplay;
		GameTime loadStartTime;
		TimeSpan loadAnimationTimer;




		/// <summary>
		/// The constructor is private: loading screens should
		/// be activated via the static Load method instead.
		/// </summary>
		private LoadingScreen(ScreenManager screenManager, bool loadingIsSlow,
				GameScreen[] screensToLoad)
		{
			this.loadingIsSlow = loadingIsSlow;
			this.screensToLoad = screensToLoad;

			TransitionOnTime = TimeSpan.FromSeconds(0.5);

			// If this is going to be a slow load operation, create a background
			// thread that will update the network session and draw the load screen
			// animation while the load is taking place.
			if (loadingIsSlow)
			{
				backgroundThread = new Thread(BackgroundWorkerThread);
				backgroundThreadExit = new ManualResetEvent(false);

				graphicsDevice = screenManager.GraphicsDevice;

				// Look up some services that will be used by the background thread.
				IServiceProvider services = screenManager.Game.Services;

				networkSession = (NetworkSession)services.GetService(
							typeof(NetworkSession));

				messageDisplay = (IMessageDisplay)services.GetService(
							typeof(IMessageDisplay));
			}
		}


		/// <summary>
		/// Activates the loading screen.
		/// </summary>
		public static void Load(ScreenManager screenManager, bool loadingIsSlow,
				PlayerIndex? controllingPlayer,
				params GameScreen[] screensToLoad)
		{
			// Tell all the current screens to transition off.
			foreach (GameScreen screen in screenManager.GetScreens())
				screen.ExitScreen();

			// Create and activate the loading screen.
			LoadingScreen loadingScreen = new LoadingScreen(screenManager,
							loadingIsSlow,
							screensToLoad);

			screenManager.AddScreen(loadingScreen, controllingPlayer);
		}





		/// <summary>
		/// Updates the loading screen.
		/// </summary>
		public override void Update(GameTime gameTime, bool otherScreenHasFocus,
							bool coveredByOtherScreen)
		{
			base.Update(gameTime, otherScreenHasFocus, coveredByOtherScreen);

			// If all the previous screens have finished transitioning
			// off, it is time to actually perform the load.
			if (otherScreensAreGone)
			{
				// Start up the background thread, which will update the network
				// session and draw the animation while we are loading.
				if (backgroundThread != null)
				{
					loadStartTime = gameTime;
					backgroundThread.Start();
				}

				// Perform the load operation.
				ScreenManager.RemoveScreen(this);

				foreach (GameScreen screen in screensToLoad)
				{
					if (screen != null)
					{
						ScreenManager.AddScreen(screen, ControllingPlayer);
					}
				}

				// Signal the background thread to exit, then wait for it to do so.
				if (backgroundThread != null)
				{
					backgroundThreadExit.Set();
					backgroundThread.Join();
				}

				// Once the load has finished, we use ResetElapsedTime to tell
				// the  game timing mechanism that we have just finished a very
				// long frame, and that it should not try to catch up.
				ScreenManager.Game.ResetElapsedTime();
			}
		}


		/// <summary>
		/// Draws the loading screen.
		/// </summary>
		public override void Draw(GameTime gameTime)
		{
			// If we are the only active screen, that means all the previous screens
			// must have finished transitioning off. We check for this in the Draw
			// method, rather than in Update, because it isn't enough just for the
			// screens to be gone: in order for the transition to look good we must
			// have actually drawn a frame without them before we perform the load.
			if ((ScreenState == ScreenState.Active) &&
		(ScreenManager.GetScreens().Length == 1))
			{
				otherScreensAreGone = true;
			}

			// The gameplay screen takes a while to load, so we display a loading
			// message while that is going on, but the menus load very quickly, and
			// it would look silly if we flashed this up for just a fraction of a
			// second while returning from the game to the menus. This parameter
			// tells us how long the loading is going to take, so we know whether
			// to bother drawing the message.
			if (loadingIsSlow)
			{
				SpriteBatch spriteBatch = ScreenManager.SpriteBatch;
				SpriteFont font = ScreenManager.Font;

				string message = Resources.Loading;

				// Center the text in the viewport.
				Viewport viewport = ScreenManager.GraphicsDevice.Viewport;
				Vector2 viewportSize = new Vector2(viewport.Width, viewport.Height);
				Vector2 textSize = font.MeasureString(message);
				Vector2 textPosition = (viewportSize - textSize) / 2;

				Color color = Color.White * TransitionAlpha;

				// Animate the number of dots after our "Loading..." message.
				loadAnimationTimer += gameTime.ElapsedGameTime;

				int dotCount = (int)(loadAnimationTimer.TotalSeconds * 5) % 10;

				message += new string('.', dotCount);

				// Draw the text.
				spriteBatch.Begin();
				spriteBatch.DrawString(font, message, textPosition, color);
				spriteBatch.End();
			}
		}





		/// <summary>
		/// Worker thread draws the loading animation and updates the network
		/// session while the load is taking place.
		/// </summary>
		void BackgroundWorkerThread()
		{
			long lastTime = Stopwatch.GetTimestamp();

			// EventWaitHandle.WaitOne will return true if the exit signal has
			// been triggered, or false if the timeout has expired. We use the
			// timeout to update at regular intervals, then break out of the
			// loop when we are signalled to exit.
			while (!backgroundThreadExit.WaitOne(1000 / 30))
			{
				//GameTime gameTime = GetGameTime (ref lastTime);

				//DrawLoadAnimation (gameTime);

				UpdateNetworkSession();
			}
		}


		//		/// <summary>
		//		/// Works out how long it has been since the last background thread update.
		//		/// </summary>
		//		GameTime GetGameTime (ref long lastTime)
		//		{
		//			long currentTime = Stopwatch.GetTimestamp ();
		//			long elapsedTicks = currentTime - lastTime;
		//			lastTime = currentTime;
		//
		//			TimeSpan elapsedTime = TimeSpan.FromTicks (elapsedTicks * 
		//						TimeSpan.TicksPerSecond / 
		//						Stopwatch.Frequency);
		//
		//			return new GameTime (loadStartTime.TotalGameTime + elapsedTime, elapsedTime);
		//		}


		/// <summary>
		/// Calls directly into our Draw method from the background worker thread,
		/// so as to update the load animation in parallel with the actual loading.
		/// </summary>
		void DrawLoadAnimation(GameTime gameTime)
		{
			if ((graphicsDevice == null) || graphicsDevice.IsDisposed)
				return;

			try
			{
				graphicsDevice.Clear(Color.Black);

				// Draw the loading screen.
				Draw(gameTime);

				// If we have a message display component, we want to display
				// that over the top of the loading screen, too.
				if (messageDisplay != null)
				{
					messageDisplay.Update(gameTime);
					messageDisplay.Draw(gameTime);
				}

				graphicsDevice.Present();
			}
			catch
			{
				// If anything went wrong (for instance the graphics device was lost
				// or reset) we don't have any good way to recover while running on a
				// background thread. Setting the device to null will stop us from
				// rendering, so the main game can deal with the problem later on.
				graphicsDevice = null;
			}
		}


		/// <summary>
		/// Updates the network session from the background worker thread, to avoid
		/// disconnecting due to network timeouts even if loading takes a long time.
		/// </summary>
		void UpdateNetworkSession()
		{
			if ((networkSession == null) ||
		(networkSession.SessionState == NetworkSessionState.Ended))
				return;

			try
			{
				networkSession.Update();
			}
			catch
			{
				// If anything went wrong, we don't have a good way to report that
				// error while running on a background thread. Setting the session to
				// null will stop us from updating it, so the main game can deal with
				// the problem later on.
				networkSession = null;
			}
		}


	}
}