MonoGame.Samples/Samples/MacOS/NetRumble/ScreenManager/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 Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
#endregion

namespace NetRumble
{
    /// <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>
    /// <remarks>
    /// This public class is similar to one in the GameStateManagement sample.
    /// </remarks>
    public class LoadingScreen : GameScreen
    {
        #region Fields

        bool loadingIsSlow;
        bool otherScreensAreGone;
        EventHandler<EventArgs> loadNextScreen;

        #endregion

        #region Initialization


        /// <summary>
        /// The constructor is private: loading screens should
        /// be activated via the static Load method instead.
        /// </summary>
        private LoadingScreen()
        {
            TransitionOnTime = TimeSpan.FromSeconds(0.5);
        }


        /// <summary>
        /// Activates the loading screen.
        /// </summary>
        public static void Load(ScreenManager screenManager,
                                EventHandler<EventArgs> loadNextScreen,
                                bool loadingIsSlow)
        {
            // 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();

            loadingScreen.loadingIsSlow = loadingIsSlow;
            loadingScreen.loadNextScreen = loadNextScreen;

            screenManager.AddScreen(loadingScreen);
        }


        #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)
            {
                ScreenManager.RemoveScreen(this);

                loadNextScreen(this, EventArgs.Empty);
            }
        }


        /// <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)
            {
                const string message = "Loading...";

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

                Color color = new Color(255, 255, 255, TransitionAlpha);

                // Draw the text.
                ScreenManager.SpriteBatch.Begin();
                
                ScreenManager.SpriteBatch.DrawString(ScreenManager.Font, message,
                                                     textPosition, color);
                
                ScreenManager.SpriteBatch.End();
            }
        }


        #endregion
    }
}