Opentk/Source/OpenTK/GameWindow.cs

#region --- License ---
/* Copyright (c) 2006, 2007 Stefanos Apostolopoulos
 * See license.txt for license info
 */
#endregion

using System;
using System.Collections.Generic;
using System.Text;
using System.Diagnostics;

using OpenTK.Platform;
using OpenTK.Input;
using System.Threading;
using OpenTK.OpenGL;
using OpenTK.OpenGL.Enums;

namespace OpenTK
{
    /// <summary>
    /// The GameWindow class contains cross-platform methods to create and render on an OpenGL
    /// window, handle input and load resources.
    /// </summary>
    /// <remarks>
    /// GameWindow contains several events you can hook or override to add your custom logic:
    /// <list>
    /// <item>
    /// OnLoad: Occurs after creating the OpenGL context, but before entering the main loop.
    /// Override to load resources.
    /// </item>
    /// <item>
    /// OnUnload: Occurs after exiting the main loop, but before deleting the OpenGL context.
    /// Override to unload resources.
    /// </item>
    /// <item>
    /// OnResize: Occurs whenever GameWindow is resized. You should update the OpenGL Viewport
    /// and Projection Matrix here.
    /// </item>
    /// <item>
    /// OnUpdateFrame: Occurs at the specified logic update rate. Override to add your game
    /// logic.
    /// </item>
    /// <item>
    /// OnRenderFrame: Occurs at the specified frame render rate. Override to add your
    /// rendering code.
    /// </item>
    /// </list>
    /// Call the Run() method to start the application's main loop. Run(double, double) takes two
    /// parameters that
    /// specify the logic update rate, and the render update rate.
    /// </remarks>
    public class GameWindow : IDisposable/* : IGameWindow*/
    {
        #region --- Fields ---

        INativeGLWindow glWindow;
        DisplayMode mode;

        ResizeEventArgs resizeEventArgs = new ResizeEventArgs();

        bool isExiting;
        bool disposed;

        double update_period, render_period;
        double target_update_period, target_render_period, target_render_period_doubled;
        // TODO: Implement these:
        double update_time, render_time, event_time;
        //bool allow_sleep = true;    // If true, GameWindow will call Timer.Sleep() if there is enough time.
        int width, height;
        VSyncMode vsync;

        //InputDriver input_driver;

        #endregion

        #region --- Internal Properties ---

        bool MustResize
        {
            get { return glWindow.Width != this.Width || glWindow.Height != this.Height; }
        }

        #endregion

        #region --- Contructors ---

        /// <summary>
        /// Constructs a new GameWindow using a safe DisplayMode.
        /// </summary>
        public GameWindow() : this(new DisplayMode(640, 480, 0, 16, false), "OpenTK game window")
        { }

        /// <summary>
        /// Constructs a new GameWindow, and opens a render window with the specified DisplayMode.
        /// </summary>
        /// <param name="mode">The DisplayMode of the GameWindow.</param>
        public GameWindow(DisplayMode mode) : this(mode, "OpenTK game window") { }

        /// <summary>
        /// Constructs a new GameWindow with the specified title, and opens a render window with the
        /// specified DisplayMode.
        /// </summary>
        /// <param name="mode">The DisplayMode of the GameWindow.</param>
        /// <param name="title">The Title of the GameWindow.</param>
        public GameWindow(DisplayMode mode, string title)
        {
            switch (Environment.OSVersion.Platform)
            {
                case PlatformID.Win32NT:
                case PlatformID.Win32S:
                case PlatformID.Win32Windows:
                case PlatformID.WinCE:
                    glWindow = new OpenTK.Platform.Windows.WinGLNative();
                    break;

                case PlatformID.Unix:
                case (PlatformID)128:
                    glWindow = new OpenTK.Platform.X11.X11GLNative();
                    break;

                default:
                    throw new PlatformNotSupportedException(
                        "Your platform is not supported currently. Please, refer to http://opentk.sourceforge.net for more information.");
            }

            glWindow.Destroy += new DestroyEvent(glWindow_Destroy);
            
            CreateWindow(mode, title);
            //this.vsync = VSyncMode.Adaptive;
            this.VSync = VSyncMode.On;
        }

        void glWindow_Destroy(object sender, EventArgs e)
        {
            glWindow.Destroy -= glWindow_Destroy;
            this.Exit();
        }

        #endregion

        #region --- INativeGLWindow Members ---

        #region public void Exit()

        /// <summary>
        /// Gracefully exits the current GameWindow.
        /// Override if you want to provide yor own exit sequence.
        /// If you override this method, place a call to base.Exit(), to ensure
        /// proper OpenTK shutdown.
        /// </summary>
        public virtual void Exit()
        {
            isExiting = true;
            throw new GameWindowExitException();
        }

        #endregion

        #region public bool IsIdle

        /// <summary>
        /// Gets a value indicating whether the current GameWindow is idle.
        /// If true, the OnUpdateFrame and OnRenderFrame functions should be called.
        /// </summary>
        public bool IsIdle
        {
            get { return glWindow.IsIdle; }
        }

        #endregion

        #region public bool Fullscreen

        /// <summary>
        /// TODO: This property is not implemented.
        /// Gets or sets a value indicating whether the GameWindow is in fullscrren mode.
        /// </summary>
        public bool Fullscreen
        {
            get { return false;/* return glWindow.Fullscreen; */ }
            set { /* glWindow.Fullscreen = value; */}
        }

        #endregion

        #region public IGLContext Context

        /// <summary>
        /// Returns the opengl IGLontext associated with the current GameWindow.
        /// Forces window creation.
        /// </summary>
        public IGLContext Context
        {
            get
            {
				if (!this.Exists && !this.IsExiting)
				{
				    Debug.WriteLine("WARNING: OpenGL Context accessed before creating a render window. This may indicate a programming error. Force-creating a render window.");
				    mode = new DisplayMode(640, 480);
				    this.CreateWindow(mode);
				}
				return glWindow.Context;
			}
        }

        #endregion

        #region public bool Exists

        /// <summary>
        /// Gets a value indicating whether a render window exists.
        /// </summary>
        public bool Exists
        {
            get { return glWindow == null ? false : glWindow.Exists; }
        }

        #endregion

        #region public string Text

        /// <summary>
        /// Gets or sets the GameWindow title.
        /// </summary>
        public string Title
        {
            get
            {
                return glWindow.Title;
            }
            set
            {
                glWindow.Title = value;
            }
        }

        #endregion

        #region public bool Visible

        /// <summary>
        /// TODO: This property is not implemented
        /// Gets or sets a value indicating whether the GameWindow is visible.
        /// </summary>
        public bool Visible
        {
            get
            {
                throw new NotImplementedException();
                //return glWindow.Visible;
            }
            set
            {
                throw new NotImplementedException();
                //glWindow.Visible = value;
            }
        }

        #endregion

        #region public IWindowInfo WindowInfo

        public IWindowInfo WindowInfo
        {
            get { return glWindow.WindowInfo; }
        }

        #endregion
        
#if false

        #region public IInputDriver InputDriver

        /// <summary>
        /// Gets an interface to the InputDriver used to obtain Keyboard, Mouse and Joystick input.
        /// </summary>
        public IInputDriver InputDriver
        {
            get
            {
                return null;
            }
        }

        #endregion

#endif

        #region public void CreateWindow(DisplayMode mode)

        /// <summary>
        /// Creates a render window for the calling GameWindow.
        /// </summary>
        /// <param name="mode">The DisplayMode of the render window.</param>
        /// <remarks>
        /// It is an error to call this function when a render window already exists.
        /// <para>Call DestroyWindow to close the render window.</para>
        /// </remarks>
        /// <exception cref="ApplicationException">Occurs when a render window already exists.</exception>
        public void CreateWindow(DisplayMode mode)
        {
            if (!Exists)
            {
                try
                {
                    glWindow.CreateWindow(mode);
                }
                catch (ApplicationException expt)
                {
                    Debug.Print(expt.ToString());
                    throw;
                }
            }
            else
            {
                throw new ApplicationException("A render window already exists for this GameWindow.");
            }
        }

        #endregion

        #region public void DestroyWindow()

        /// <summary>
        /// Destroys the GameWindow. The Destroy event is raised before destruction commences
        /// (while the opengl context still exists), to allow resource cleanup.
        /// </summary>
        public void DestroyWindow()
        {
            if (Exists)
                glWindow.DestroyWindow();
            else
                throw new ApplicationException("Tried to destroy non-existent window.");
        }

        #endregion

        #endregion

        #region --- GameWindow Methods ---

        #region public void CreateWindow(DisplayMode mode, string title)

        /// <summary>
        /// Creates a render window for the calling GameWindow, with the specified DisplayMode and Title.
        /// </summary>
        /// <param name="mode">The DisplayMode of the render window.</param>
        /// <param name="title">The Title of the render window.</param>
        /// <remarks>
        /// It is an error to call this function when a render window already exists.
        /// <para>Call DestroyWindow to close the render window.</para>
        /// </remarks>
        /// <exception cref="ApplicationException">Occurs when a render window already exists.</exception>
        private void CreateWindow(DisplayMode mode, string title)
        {
            if (!Exists)
            {
                try
                {
                    glWindow.CreateWindow(mode);
                    this.Title = title;
                    //input_driver = new InputDriver(this);
                }
                catch (ApplicationException expt)
                {
                    Debug.Print(expt.ToString());
                    throw;
                }
            }
            else
            {
                throw new InvalidOperationException("A render window already exists for this GameWindow.");
            }
        }

        #endregion

        #region void Run()

        /// <summary>
        /// Enters the game loop of the GameWindow updating and rendering at the maximum possible frequency.
        /// </summary>
        /// <see cref="public virtual void Run(double update_frequency, double render_frequency)"/>
        public void Run()
        {
            Run(0.0, 0.0);
        }

        /// <summary>
        /// Enters the game loop of the GameWindow updating the specified update frequency, while maintaining the
        /// maximum possible render frequency.
        /// </summary>
        /// <see cref="public virtual void Run(double updateFrequency, double renderFrequency)"/>
        public void Run(double updateFrequency)
        {
            Run(updateFrequency, 0.0);
        }

        /// <summary>
        /// Enters the game loop of the GameWindow updating and rendering at the specified frequency.
        /// </summary>
        /// <param name="updates_per_second">The frequency of UpdateFrame events.</param>
        /// <param name="frames_per_second">The frequency of RenderFrame events.</param>
        public void Run(double updates_per_second, double frames_per_second)
        {
            try
            {
                if (updates_per_second < 0.0 || updates_per_second > 200.0)
                    throw new ArgumentOutOfRangeException("updates_per_second", updates_per_second, "Parameter should be inside the range [0.0, 200.0]");
                if (frames_per_second < 0.0 || frames_per_second > 200.0)
                    throw new ArgumentOutOfRangeException("frames_per_second", frames_per_second, "Parameter should be inside the range [0.0, 200.0]");

                TargetUpdateFrequency = updates_per_second;
                TargetRenderFrequency = frames_per_second;

                Stopwatch update_watch = new Stopwatch(), render_watch = new Stopwatch();
                double time, next_render = 0.0, next_update = 0.0, update_time_counter = 0.0;
                int num_updates = 0;
                UpdateFrameEventArgs update_args = new UpdateFrameEventArgs();
                RenderFrameEventArgs render_args = new RenderFrameEventArgs();

                //double sleep_granularity;      // In seconds.

                //GC.Collect(2);
                //GC.WaitForPendingFinalizers();
                //GC.Collect(2);

                // Find the minimum granularity of the Thread.Sleep() function.
                // TODO: Disabled - see comment on Thread.Sleep() problems below.
                //update_watch.Start();
                //const int test_times = 5;
                //for (int i = test_times; --i > 0; )
                //    Thread.Sleep(1);
                //update_watch.Stop();
                //sleep_granularity = System.Math.Round(1000.0 * update_watch.Elapsed.TotalSeconds / test_times, MidpointRounding.AwayFromZero) / 1000.0;
                //update_watch.Reset();       // We don't want to affect the first UpdateFrame!

                try
                {
                    OnLoadInternal(EventArgs.Empty);
                }
                catch (Exception e)
                {
                    Trace.WriteLine(String.Format("OnLoad failed: {0}", e.ToString()));
                    return;
                }

                Debug.Print("Elevating priority.");
                Thread.CurrentThread.Priority = ThreadPriority.AboveNormal;
                
                Debug.Print("Entering main loop.");
                while (!isExiting)
                {
                    // Process events
                    ProcessEvents();

                    // Raise UpdateFrame events
                    time = update_watch.Elapsed.TotalSeconds;
                    if (time > 1.0)
                        time = 1.0;
                    while (next_update - time <= 0.0)
                    {
                        next_update = next_update - time + TargetUpdatePeriod;
                        if (next_update < -1.0)       // Cap the maximum time drift, to avoid lengthy catch-up games.
                            next_update = -1.0;

                        update_time_counter += time;
                        ++num_updates;

                        update_watch.Reset();
                        update_watch.Start();

                        update_args.Time = time;
                        OnUpdateFrameInternal(update_args);
                        update_time = update_watch.Elapsed.TotalSeconds;

                        if (TargetUpdateFrequency == 0.0)
                            break;

                        time = update_watch.Elapsed.TotalSeconds;
                        next_update -= time;
                        update_time_counter += time;

                        // Allow up to 10 frames to be dropped. Prevents the application from hanging
                        // with very high update frequencies.
                        if (num_updates >= 10)
                            break;
                    }
                    if (num_updates > 0)
                    {
                        update_period = update_time_counter / (double)num_updates;
                        num_updates = 0;
                        update_time_counter = 0.0;
                    }

                    //if (isExiting)
                    //    break;

                    // Raise RenderFrame event
                    time = render_watch.Elapsed.TotalSeconds;
                    if (time > 1.0)
                        time = 1.0;
                    double time_left = next_render - time;
                    if (VSync == VSyncMode.Adaptive)
                    {
                        // Check if we have enough time for a vsync
                        if (RenderTime > 2.0 * TargetRenderPeriod)
                            Context.VSync = false;
                        else
                            Context.VSync = true;
                    }

                    if (time_left <= 0.0)
                    {
                        next_render = time_left + TargetRenderPeriod;
                        if (next_render < -1.0)       // Cap the maximum time drift, to avoid lengthy catch-up games.
                            next_render = -1.0;

                        render_watch.Reset();
                        render_watch.Start();

                        render_period = render_args.Time = time;
                        render_args.ScaleFactor = RenderPeriod / UpdatePeriod;
                        OnRenderFrameInternal(render_args);
                        render_time = render_watch.Elapsed.TotalSeconds;
                    }

                    // Yield CPU time, if the Thread.Sleep() granularity allows it.
                    // TODO: Disabled because it does not work reliably enough on all systems.
                    // Enable vsync as a workaround.
                    //if (AllowSleep && next_render > sleep_granularity && next_update > sleep_granularity)
                    //{
                    //    Thread.Sleep((int)(1000.0 * System.Math.Min(next_render - sleep_granularity, next_update - sleep_granularity)));
                    //}
                }
            }
            catch (GameWindowExitException)
            {
                Trace.WriteLine("Exiting main loop.");
            }
            finally
            {
                Debug.Print("Restoring priority.");
                Thread.CurrentThread.Priority = ThreadPriority.Normal;

                OnUnloadInternal(EventArgs.Empty);

                if (this.Exists)
                {
                    if (Exists)
                        glWindow.DestroyWindow();
                    while (this.Exists)
                        this.ProcessEvents();
                }
            }
        }

        #endregion

        #region public void ProcessEvents()

        /// <summary>
        /// Processes operating system events until the GameWindow becomes idle.
        /// </summary>
        /// <remarks>
        /// When overriding the default GameWindow game loop (provided by the Run() function)
        /// you should call ProcessEvents() to ensure that your GameWindow responds to
        /// operating system events.
        /// <para>
        /// Once ProcessEvents() returns, it is time to call update and render the next frame.
        /// </para>
        /// </remarks>
        public void ProcessEvents()
        {
            //if (!isExiting)
            //    InputDriver.Poll();
            glWindow.ProcessEvents();

            if (MustResize)
            {
                resizeEventArgs.Width = glWindow.Width;
                resizeEventArgs.Height = glWindow.Height;
                OnResizeInternal(resizeEventArgs);
            }
        }

        #endregion

        #region OnRenderFrame(RenderFrameEventArgs e)

        /// <summary>
        /// Raises the RenderFrame event, and calls the public function.
        /// </summary>
        /// <param name="e"></param>
        private void OnRenderFrameInternal(RenderFrameEventArgs e)
        {
            if (!this.Exists && !this.IsExiting)
            {
                Debug.Print("WARNING: RenderFrame event raised, without a valid render window. This may indicate a programming error. Creating render window.");
                mode = new DisplayMode(640, 480);
                this.CreateWindow(mode);
            }
            if (RenderFrame != null)
                RenderFrame(this, e);

            // Call the user's override.
            OnRenderFrame(e);
        }

        /// <summary>
        /// Override in derived classes to render a frame.
        /// </summary>
        /// <param name="e">Contains information necessary for frame rendering.</param>
        /// <remarks>
        /// The base implementation (base.OnRenderFrame) is empty, there is no need to call it.
        /// </remarks>
        public virtual void OnRenderFrame(RenderFrameEventArgs e)
        {
        }

        /// <summary>
        /// Occurs when it is time to render the next frame.
        /// </summary>
        public event RenderFrameEvent RenderFrame;

        #endregion

        #region OnUpdateFrame(UpdateFrameEventArgs e)

        private void OnUpdateFrameInternal(UpdateFrameEventArgs e)
        {
            if (!this.Exists && !this.IsExiting)
            {
                //Debug.Print("WARNING: UpdateFrame event raised without a valid render window. This may indicate a programming error. Creating render window.");
                //mode = new DisplayMode(640, 480);
                //this.CreateWindow(mode);
                throw new InvalidOperationException("Cannot enter game loop without a render window");
            }

            if (UpdateFrame != null)
            {
                UpdateFrame(this, e);
            }

            OnUpdateFrame(e);
        }

        /// <summary>
        /// Override in derived classes to update a frame.
        /// </summary>
        /// <param name="e">Contains information necessary for frame updating.</param>
        /// <remarks>
        /// The base implementation (base.OnUpdateFrame) is empty, there is no need to call it.
        /// </remarks>
        public virtual void OnUpdateFrame(UpdateFrameEventArgs e)
        {
        }

        /// <summary>
        /// Occurs when it is time to update the next frame.
        /// </summary>
        public event UpdateFrameEvent UpdateFrame;

        #endregion

        #region OnLoad(EventArgs e)

        /// <summary>
        /// Occurs after establishing an OpenGL context, but before entering the main loop.
        /// </summary>
        public event LoadEvent Load;

        /// <summary>
        /// Raises the Load event, and calls the user's OnLoad override.
        /// </summary>
        /// <param name="e"></param>
        private void OnLoadInternal(EventArgs e)
        {
            if (MustResize)
            {
                resizeEventArgs.Width = glWindow.Width;
                resizeEventArgs.Height = glWindow.Height;
                OnResizeInternal(resizeEventArgs);
            }

            Debug.WriteLine(String.Format("OpenGL driver information: {0}, {1}, {2}",
                GL.GetString(StringName.Renderer),
                GL.GetString(StringName.Vendor),
                GL.GetString(StringName.Version)));

            if (this.Load != null)
            {
                this.Load(this, e);
            }

            OnLoad(e);
        }

        /// <summary>
        /// Occurs after establishing an OpenGL context, but before entering the main loop.
        /// Override to load resources that should be maintained for the lifetime of the application.
        /// </summary>
        /// <param name="e">Not used.</param>
        public virtual void OnLoad(EventArgs e)
        {
        }

        #endregion

        #region OnUnload(EventArgs e)

        /// <summary>
        /// Occurs after after calling GameWindow.Exit, but before destroying the OpenGL context.
        /// </summary>
        public event UnloadEvent Unload;

        /// <summary>
        /// Raises the Unload event, and calls the user's OnUnload override.
        /// </summary>
        /// <param name="e"></param>
        private void OnUnloadInternal(EventArgs e)
        {
            if (this.Unload != null)
            {
                this.Unload(this, e);
            }

            OnUnload(e);
        }

        /// <summary>
        /// Occurs after after calling GameWindow.Exit, but before destroying the OpenGL context.
        /// Override to unload application resources.
        /// </summary>
        /// <param name="e">Not used.</param>
        public virtual void OnUnload(EventArgs e)
        {
        }

        #endregion

        #region public bool IsExiting

        /// <summary>
        /// Gets a value indicating whether the shutdown sequence has been initiated
        /// for this window, by calling GameWindow.Exit() or hitting the 'close' button.
        /// If this property is true, it is no longer safe to use any OpenTK.Input or
        /// OpenTK.OpenGL functions or properties.
        /// </summary>
        public bool IsExiting
        {
            get { return isExiting; }
        }

        #endregion

        #region public Keyboard Keyboard

        /// <summary>
        /// Gets the primary Keyboard device, or null if no Keyboard exists.
        /// </summary>
        public KeyboardDevice Keyboard
        {
            get
            {
                //if (input_driver.Keyboard.Count > 0)
                //    return input_driver.Keyboard[0];
                //else
                //    return null;
                
                if (glWindow.InputDriver.Keyboard.Count > 0)
                    return glWindow.InputDriver.Keyboard[0];
                else
                    return null;
            }
        }

        #endregion

        #region public Mouse Mouse

        /// <summary>
        /// Gets the primary Mouse device, or null if no Mouse exists.
        /// </summary>
        public MouseDevice Mouse
        {
            get
            {
                //if (input_driver.Mouse.Count > 0)
                //    return input_driver.Mouse[0];
                //else
                //    return null;

                if (glWindow.InputDriver.Mouse.Count > 0)
                    return glWindow.InputDriver.Mouse[0];
                else
                    return null;
            }
        }

        #endregion

        #region public VSyncMode VSync

        /// <summary>
        /// Gets or sets the VSyncMode.
        /// </summary>
        public VSyncMode VSync
        {
            get
            {
                return vsync;
            }
            set
            {
                if (value == VSyncMode.Off)
                    Context.VSync = false;
                else
                    Context.VSync = true;

                vsync = value;
            }
        }

        #endregion

        #region public void SwapBuffers()

        /// <summary>
        /// Swaps the front and back buffer, presenting the rendered scene to the user.
        /// Only useful in double- or triple-buffered formats.
        /// </summary>
        /// <remarks>Calling this function is equivalent to calling Context.SwapBuffers()</remarks>
        public void SwapBuffers()
        {
            Context.SwapBuffers();
        }

        #endregion

        #endregion

        #region --- GameWindow Timing ---

        // TODO: Disabled because it is not reliable enough. Use vsync as a workaround.

        //#region public bool AllowSleep

        //public bool AllowSleep
        //{
        //    get { return allow_sleep; }
        //    set { allow_sleep = value; }
        //}

        //#endregion

        #region public double TargetRenderPeriod

        /// <summary>
        /// Gets or sets a double representing the target render period, in seconds.
        /// </summary>
        /// <para>A value of 0.0 indicates that RenderFrame events are generated at the maximum possible frequency (i.e. only limited by the hardware's capabilities).</para>
        /// <para>Values lower than 0.005 seconds (200Hz) are clamped to 0.0. Values higher than 1.0 seconds (1Hz) are clamped to 1.0.</para>
        /// </remarks>
        public double TargetRenderPeriod
        {
            get
            {
                return target_render_period;
            }
            set
            {
                if (value <= 0.005)
                {
                    target_render_period = target_render_period_doubled = 0.0;
                }
                else if (value <= 1.0)
                {
                    target_render_period = value;
                    target_render_period_doubled = 2.0 * target_render_period;
                }
                else Debug.Print("Target render period clamped to 1.0 seconds.");
            }
        }

        #endregion

        #region public double TargetRenderFrequency

        /// <summary>
        /// Gets or sets a double representing the target render frequency, in Herz.
        /// </summary>
        /// <remarks>
        /// <para>A value of 0.0 indicates that RenderFrame events are generated at the maximum possible frequency (i.e. only limited by the hardware's capabilities).</para>
        /// <para>Values lower than 1.0Hz are clamped to 1.0Hz. Values higher than 200.0Hz are clamped to 200.0Hz.</para>
        /// </remarks>
        public double TargetRenderFrequency
        {
            get
            {
                if (TargetRenderPeriod == 0.0)
                    return 0.0;
                return 1.0 / TargetRenderPeriod;
            }
            set
            {
                if (value < 1.0)
                {
                    TargetRenderPeriod = 0.0;
                }
                else if (value <= 200.0)
                {
                    TargetRenderPeriod = 1.0 / value;
                }
                else Debug.Print("Target render frequency clamped to 200.0Hz.");
            }
        }

        #endregion

        #region public double TargetUpdatePeriod

        /// <summary>
        /// Gets or sets a double representing the target update period, in seconds.
        /// </summary>
        /// <remarks>
        /// <para>A value of 0.0 indicates that UpdateFrame events are generated at the maximum possible frequency (i.e. only limited by the hardware's capabilities).</para>
        /// <para>Values lower than 0.005 seconds (200Hz) are clamped to 0.0. Values higher than 1.0 seconds (1Hz) are clamped to 1.0.</para>
        /// </remarks>
        public double TargetUpdatePeriod
        {
            get
            {
                return target_update_period;
            }
            set
            {
                if (value <= 0.005)
                {
                    target_update_period = 0.0;
                }
                else if (value <= 1.0)
                {
                    target_update_period = value;
                }
                else Debug.Print("Target update period clamped to 1.0 seconds.");
            }
        }

        #endregion

        #region public double TargetUpdateFrequency

        /// <summary>
        /// Gets or sets a double representing the target update frequency, in Herz.
        /// </summary>
        /// <remarks>
        /// <para>A value of 0.0 indicates that UpdateFrame events are generated at the maximum possible frequency (i.e. only limited by the hardware's capabilities).</para>
        /// <para>Values lower than 1.0Hz are clamped to 1.0Hz. Values higher than 200.0Hz are clamped to 200.0Hz.</para>
        /// </remarks>
        public double TargetUpdateFrequency
        {
            get
            {
                if (TargetUpdatePeriod == 0.0)
                    return 0.0;
                return 1.0 / TargetUpdatePeriod;
            }
            set
            {
                if (value < 1.0)
                {
                    TargetUpdatePeriod = 0.0;
                }
                else if (value <= 200.0)
                {
                    TargetUpdatePeriod = 1.0 / value;
                }
                else Debug.Print("Target update frequency clamped to 200.0Hz.");
            }
        }

        #endregion

        #region public double RenderFrequency

        /// <summary>
        /// Gets a double representing the actual frequency of RenderFrame events, in Herz (i.e. FPS or Frames Per Second).
        /// </summary>
        public double RenderFrequency
        {
            get
            {
                if (render_period == 0.0)
                    return 1.0;
                return 1.0 / render_period;
            }
        }

        #endregion

        #region public double RenderPeriod

        /// <summary>
        /// Gets a double representing the period of RenderFrame events, in seconds.
        /// </summary>
        public double RenderPeriod
        {
            get
            {
                return render_period;
            }
        }

        #endregion

        #region public double UpdateFrequency

        /// <summary>
        /// Gets a double representing the frequency of UpdateFrame events, in Herz.
        /// </summary>
        public double UpdateFrequency
        {
            get
            {
                if (update_period == 0.0)
                    return 1.0;
                return 1.0 / update_period;
            }
        }

        #endregion

        #region public double UpdatePeriod

        /// <summary>
        /// Gets a double representing the period of UpdateFrame events, in seconds.
        /// </summary>
        public double UpdatePeriod
        {
            get
            {
                return update_period;
            }
        }

        #endregion

        #region public double RenderTime

        /// <summary>
        /// Gets a double representing the time spent in the RenderFrame function, in seconds.
        /// </summary>
        public double RenderTime
        {
            get { return render_time; }
            protected set { render_time = value; }
        }

        #endregion

        #region public double RenderTime

        /// <summary>
        /// Gets a double representing the time spent in the UpdateFrame function, in seconds.
        /// </summary>
        public double UpdateTime
        {
            get { return update_time; }
        }

        #endregion

        #endregion

        #region --- IResizable Members ---

        #region public int Width, Height

        /// <summary>
        /// Gets or sets the Width of the GameWindow's rendering area, in pixels.
        /// </summary>
        public int Width
        {
            get { return width; }
            set
            {
                if (value == this.Width)
                {
                    return;
                }
                else if (value > 0)
                {
                    glWindow.Width = value;
                }
                else
                {
                    throw new ArgumentOutOfRangeException(
                        "Width",
                        value,
                        "Width must be greater than 0"
                    );
                }
            }
        }

        /// <summary>
        /// Gets or sets the Height of the GameWindow's rendering area, in pixels.
        /// </summary>
        public int Height
        {
            get { return height; }
            set
            {
                if (value == this.Height)
                {
                    return;
                }
                else if (value > 0)
                {
                    glWindow.Height = value;
                }
                else
                {
                    throw new ArgumentOutOfRangeException(
                        "Height",
                        value,
                        "Height must be greater than 0"
                    );
                }
            }
        }

        #endregion

        #region public event ResizeEvent Resize;

        /// <summary>
        /// Occurs when the GameWindow is resized. Derived classes should override the OnResize method for better performance.
        /// </summary>
        public event ResizeEvent Resize;

        /// <summary>
        /// Raises the Resize event.
        /// </summary>
        /// <param name="e">Contains information about the Resize event.</param>
        private void OnResizeInternal(ResizeEventArgs e)
        {
            Debug.Print("Firing GameWindow.Resize event: {0}.", e.ToString());

            this.width = e.Width;
            this.height = e.Height;
            
            if (this.Resize != null)
                this.Resize(this, e);

            OnResize(e);
        }

        /// <summary>
        /// Override in derived classes to respond to the Resize events.
        /// </summary>
        /// <param name="e">Contains information about the Resize event.</param>
        protected virtual void OnResize(ResizeEventArgs e)
        {
        }

        #endregion
        /*
        /// <summary>
        /// Gets the Top coordinate of the GameWindow's rendering area, in pixel coordinates relative to the GameWindow's top left point.
        /// </summary>
        public int Top
        {
            get { return glWindow.Top; }
        }

        /// <summary>
        /// /// Gets the Bottom coordinate of the GameWindow's rendering area, in pixel coordinates relative to the GameWindow's top left point.
        /// </summary>
        public int Bottom
        {
            get { return glWindow.Bottom; }
        }

        /// <summary>
        /// Gets the Left coordinate of the GameWindow's rendering area, in pixel coordinates relative to the GameWindow's top left point.
        /// </summary>
        public int Left
        {
            get { return glWindow.Left; }
        }

        /// <summary>
        /// Gets the Right coordinate of the GameWindow's rendering area, in pixel coordinates relative to the GameWindow's top left point.
        /// </summary>
        public int Right
        {
            get { return glWindow.Right; }
        }
        */
        #endregion

        #region --- IDisposable Members ---

        /// <summary>
        /// Not used yet.
        /// </summary>
        private void DisposeInternal()
        {
            Dispose();                  // User overridable Dispose method.

        }

        /// <summary>
        /// Disposes of the GameWindow, releasing all resources consumed by it.
        /// </summary>
        public virtual void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        private void Dispose(bool manual)
        {
            if (!disposed)
            {
                if (manual)
                {
                    if (glWindow != null)
                    {
                        glWindow.Dispose();
                        glWindow = null;
                    }
                }
                disposed = true;
            }
        }

        ~GameWindow()
        {
            Dispose(false);
        }

        #endregion
    }

    #region public enum VSyncMode

    /// <summary>
    /// Enumerates the available VSync modes.
    /// </summary>
    public enum VSyncMode
    {
        /// <summary>
        /// Vsync disabled.
        /// </summary>
        Off = 0,
        /// <summary>
        /// VSync enabled.
        /// </summary>
        On,
        /// <summary>
        /// VSync enabled, but automatically disabled if framerate falls below a specified limit.
        /// </summary>
        Adaptive,
    }

    #endregion

    #region --- GameWindow Events ---

    public delegate void UpdateFrameEvent(GameWindow sender, UpdateFrameEventArgs e);
    public delegate void RenderFrameEvent(GameWindow sender, RenderFrameEventArgs e);
    public delegate void LoadEvent(GameWindow sender, EventArgs e);
    public delegate void UnloadEvent(GameWindow sender, EventArgs e);

    public class UpdateFrameEventArgs : EventArgs
    {
        private double time;

        /// <summary>
        /// Gets the Time elapsed between frame updates, in seconds.
        /// </summary>
        public double Time
        {
            get { return time; }
            internal set { time = value; }
        }
    }

    public class RenderFrameEventArgs : EventArgs
    {
        private double time;
        private double scale_factor;

        /// <summary>
        /// Gets the Time elapsed between frame updates, in seconds.
        /// </summary>
        public double Time
        {
            get { return time; }
            internal set { time = value; }
        }

        public double ScaleFactor
        {
            get
            {
                return scale_factor;
            }
            internal set
            {
                if (value != 0.0 && !Double.IsNaN(value))
                    scale_factor = value;
                else
                    scale_factor = 1.0;
            }
        }
    }

    #endregion

    #region --- GameWindow Exceptions ---

    class GameWindowExitException : ApplicationException
    {
        public override string Message
        {
            get
            {
                return "GameWindow exit event. If this is caught in Visual Studio, don't worry - this is perfectly normal.";
            }
        }
    }

    #endregion
}