MonoGame.Samples/CatapultNetWars/Screens/LoadingScreen.cs

#region File Description
//-----------------------------------------------------------------------------
// LoadingScreen.cs
//
// Microsoft XNA Community Game Platform
// Copyright (C) Microsoft Corporation. All rights reserved.
//-----------------------------------------------------------------------------
#endregion

#region Using Statements
using System;
using System.Threading;
using System.Diagnostics;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Net;
using GameStateManagement;
#endregion

namespace CatapultGame
{
	/// <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
	{
	#region Fields

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

	#endregion

	#region Initialization


		/// <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);
		}


	#endregion

	#region Update and Draw


		/// <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 ();
			}
		}


	#endregion

	#region Background Thread


		/// <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;
			}
		}


	#endregion
	}
}