#region License
//
// The Open Toolkit Library License
//
// Copyright (c) 2006 - 2009 the Open Toolkit library.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights to 
// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
// the Software, and to permit persons to whom the Software is furnished to do
// so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.
//
#endregion

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Drawing;
using System.Threading;
using OpenTK.Graphics;
using OpenTK.Input;
using OpenTK.Platform;

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 : NativeWindow, IGameWindow, IDisposable
    {
        #region --- Fields ---

        //DisplayMode mode; // TODO: Removable?

        object exit_lock = new object();

        IGraphicsContext glContext;

        bool hasMainLoop;
        bool isExiting = false;

        int main_loop_thread_id;

        double update_period, render_period;
        double target_update_period, target_render_period;
        // 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.
        VSyncMode vsync;

        //InputDriver input_driver;

        #endregion

        #region --- Contructors ---

        #region public GameWindow()

        /// <summary>Constructs a new GameWindow with sensible default attributes.</summary>
        public GameWindow()
            : this(640, 480, GraphicsMode.Default, "OpenTK Game Window", 0, DisplayDevice.Default) { }

        #endregion

        #region public GameWindow(int width, int height)

        /// <summary>Constructs a new GameWindow with the specified attributes.</summary>
        /// <param name="width">The width of the GameWindow in pixels.</param>
        /// <param name="height">The height of the GameWindow in pixels.</param>
        public GameWindow(int width, int height)
            : this(width, height, GraphicsMode.Default, "OpenTK Game Window", 0, DisplayDevice.Default) { }

        #endregion

        #region public GameWindow(int width, int height, GraphicsMode mode)

        /// <summary>Constructs a new GameWindow with the specified attributes.</summary>
        /// <param name="width">The width of the GameWindow in pixels.</param>
        /// <param name="height">The height of the GameWindow in pixels.</param>
        /// <param name="mode">The OpenTK.Graphics.GraphicsMode of the GameWindow.</param>
        public GameWindow(int width, int height, GraphicsMode mode)
            : this(width, height, mode, "OpenTK Game Window", 0, DisplayDevice.Default) { }

        #endregion

        #region public GameWindow(int width, int height, GraphicsMode mode, string title)

        /// <summary>Constructs a new GameWindow with the specified attributes.</summary>
        /// <param name="width">The width of the GameWindow in pixels.</param>
        /// <param name="height">The height of the GameWindow in pixels.</param>
        /// <param name="mode">The OpenTK.Graphics.GraphicsMode of the GameWindow.</param>
        /// <param name="title">The title of the GameWindow.</param>
        public GameWindow(int width, int height, GraphicsMode mode, string title)
            : this(width, height, mode, title, 0, DisplayDevice.Default) { }

        #endregion

        #region public GameWindow(int width, int height, GraphicsMode mode, string title, GameWindowFlags options)

        /// <summary>Constructs a new GameWindow with the specified attributes.</summary>
        /// <param name="width">The width of the GameWindow in pixels.</param>
        /// <param name="height">The height of the GameWindow in pixels.</param>
        /// <param name="mode">The OpenTK.Graphics.GraphicsMode of the GameWindow.</param>
        /// <param name="title">The title of the GameWindow.</param>
        /// <param name="options">GameWindow options regarding window appearance and behavior.</param>
        public GameWindow(int width, int height, GraphicsMode mode, string title, GameWindowFlags options)
            : this(width, height, mode, title, options, DisplayDevice.Default) { }

        #endregion

        #region public GameWindow(int width, int height, GraphicsMode mode, string title, GameWindowFlags options, DisplayDevice device)

        /// <summary>Constructs a new GameWindow with the specified attributes.</summary>
        /// <param name="width">The width of the GameWindow in pixels.</param>
        /// <param name="height">The height of the GameWindow in pixels.</param>
        /// <param name="mode">The OpenTK.Graphics.GraphicsMode of the GameWindow.</param>
        /// <param name="title">The title of the GameWindow.</param>
        /// <param name="options">GameWindow options regarding window appearance and behavior.</param>
        /// <param name="device">The OpenTK.Graphics.DisplayDevice to construct the GameWindow in.</param>
        public GameWindow(int width, int height, GraphicsMode mode, string title, GameWindowFlags options, DisplayDevice device)
            : this(width, height, mode, title, options, device, 1, 0, GraphicsContextFlags.Default)
        { }

        #endregion

        #region public GameWindow(int width, int height, GraphicsMode mode, string title, GameWindowFlags options, DisplayDevice device, int major, int minor, GraphicsContextFlags flags)

        /// <summary>Constructs a new GameWindow with the specified attributes.</summary>
        /// <param name="width">The width of the GameWindow in pixels.</param>
        /// <param name="height">The height of the GameWindow in pixels.</param>
        /// <param name="mode">The OpenTK.Graphics.GraphicsMode of the GameWindow.</param>
        /// <param name="title">The title of the GameWindow.</param>
        /// <param name="options">GameWindow options regarding window appearance and behavior.</param>
        /// <param name="device">The OpenTK.Graphics.DisplayDevice to construct the GameWindow in.</param>
        /// <param name="major">The major version for the OpenGL GraphicsContext.</param>
        /// <param name="minor">The minor version for the OpenGL GraphicsContext.</param>
        /// <param name="flags">The GraphicsContextFlags version for the OpenGL GraphicsContext.</param>
        public GameWindow(int width, int height, GraphicsMode mode, string title, GameWindowFlags options, DisplayDevice device,
            int major, int minor, GraphicsContextFlags flags)
            : this(width, height, mode, title, options, device, major, minor, flags, null)
        { }

        #endregion

        #region public GameWindow(int width, int height, GraphicsMode mode, string title, GameWindowFlags options, DisplayDevice device, int major, int minor, GraphicsContextFlags flags, IGraphicsContext sharedContext)

        /// <summary>Constructs a new GameWindow with the specified attributes.</summary>
        /// <param name="width">The width of the GameWindow in pixels.</param>
        /// <param name="height">The height of the GameWindow in pixels.</param>
        /// <param name="mode">The OpenTK.Graphics.GraphicsMode of the GameWindow.</param>
        /// <param name="title">The title of the GameWindow.</param>
        /// <param name="options">GameWindow options regarding window appearance and behavior.</param>
        /// <param name="device">The OpenTK.Graphics.DisplayDevice to construct the GameWindow in.</param>
        /// <param name="major">The major version for the OpenGL GraphicsContext.</param>
        /// <param name="minor">The minor version for the OpenGL GraphicsContext.</param>
        /// <param name="flags">The GraphicsContextFlags version for the OpenGL GraphicsContext.</param>
        /// <param name="sharedContext">An IGraphicsContext to share resources with.</param>
        public GameWindow(int width, int height, GraphicsMode mode, string title, GameWindowFlags options, DisplayDevice device,
                          int major, int minor, GraphicsContextFlags flags, IGraphicsContext sharedContext)
            : base(width, height, title, options,
                   mode == null ? GraphicsMode.Default : mode,
                   device == null ? DisplayDevice.Default : device)
        {
            try
            {
                glContext = new GraphicsContext(mode == null ? GraphicsMode.Default : mode, WindowInfo, major, minor, flags);
                glContext.MakeCurrent(WindowInfo);
                (glContext as IGraphicsContextInternal).LoadAll();

                VSync = VSyncMode.On;

                //glWindow.WindowInfoChanged += delegate(object sender, EventArgs e) { OnWindowInfoChangedInternal(e); };
                EnableEvents();
            }
            catch (Exception e)
            {
                Debug.Print(e.ToString());
                base.Dispose();
                throw;
            }
        }

        #endregion

        #endregion

        #region --- Public Members ---

        #region Methods

        #region Dispose

        /// <summary>
        /// Disposes of the GameWindow, releasing all resources consumed by it.
        /// </summary>
        public new void Dispose()
        {
            try
            {
                Dispose(true);
            }
            finally
            {
                if (!IsDisposed())
                {
                    if (glContext != null)
                    {
                        glContext.Dispose();
                        glContext = null;
                    }

                    base.Dispose();
                }
            }
            GC.SuppressFinalize(this);
        }

        #endregion

        #region Exit

        /// <summary>
        /// Gracefully exits the GameWindow. May be called from any thread.
        /// </summary>
        /// <remarks>
        /// <para>Override if you are not using <see cref="GameWindow.Run()"/>.</para>
        /// <para>If you override this method, place a call to base.Exit(), to ensure proper OpenTK shutdown.</para>
        /// </remarks>
        public virtual void Exit()
        {
            Close();
        }

        #endregion

        #region MakeCurrent

        /// <summary>
        /// Makes the GraphicsContext current on the calling thread.
        /// </summary>
        public void MakeCurrent()
        {
            EnsureUndisposed();
            Context.MakeCurrent(WindowInfo);
        }

        #endregion

        #region OnLoad

        /// <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)
        {
            EnsureUndisposed(); //if (disposed) throw new ObjectDisposedException("GameWindow"); // What is the exact purpose?
        }

        #endregion

        #region OnUnload

        /// <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)
        {
            EnsureUndisposed(); //if (disposed) throw new ObjectDisposedException("GameWindow"); // What is the exact purpose?
        }

        #endregion

        #region public void Run()

        /// <summary>
        /// Enters the game loop of the GameWindow using the maximum update rate.
        /// </summary>
        /// <seealso cref="Run(double)"/>
        public void Run()
        {
            Run(0.0, 0.0);
        }

        #endregion

        #region public void Run(double updateFrequency)

        /// <summary>
        /// Enters the game loop of the GameWindow using the specified update rate.
        /// maximum possible render frequency.
        /// </summary>
        public void Run(double updateRate)
        {
            Run(updateRate, 0.0);
        }

        #endregion

        #region public void Run(double updates_per_second, double frames_per_second)

        /// <summary>
        /// Enters the game loop of the GameWindow updating and rendering at the specified frequency.
        /// </summary>
        /// <remarks>
        /// When overriding the default game loop 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>
        /// <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)
        {
            EnsureUndisposed();

            try
            {
                // Necessary to be here, otherwise Exit() wouldn't work correctly when called inside OnLoad().
                hasMainLoop = true;
                main_loop_thread_id = Thread.CurrentThread.ManagedThreadId;

                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;
                FrameEventArgs update_args = new FrameEventArgs();
                FrameEventArgs render_args = new FrameEventArgs();

                update_watch.Reset();
                render_watch.Reset();

                OnLoadInternal(EventArgs.Empty);

                Debug.Print("Entering main loop.");
                while (!IsExiting && Exists && HasMainLoop)
                {
                    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();

                        if (time > 0)
                        {
                            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;
                    }

                    // 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 (TargetRenderPeriod != 0 && 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();

                        if (time > 0)
                        {
                            render_period = render_args.Time = time;
                            OnRenderFrameInternal(render_args);
                            render_time = render_watch.Elapsed.TotalSeconds;
                        }
                    }
                }
            }
            finally
            {
                Debug.Print("Restoring priority.");
                Thread.CurrentThread.Priority = ThreadPriority.Normal;

                OnUnloadInternal(EventArgs.Empty);

                if (Exists)
                {
                    Dispose();
                    //while (this.Exists) ProcessEvents(); // TODO: Should similar behaviour be retained, possibly on native window level?
                }
            }
        }

        #endregion

        #region SwapBuffers

        /// <summary>
        /// Swaps the front and back buffer, presenting the rendered scene to the user.
        /// </summary>
        public void SwapBuffers()
        {
            EnsureUndisposed();
            this.Context.SwapBuffers();
        }

        #endregion

        #endregion

        #region Properties

        #region Context

        /// <summary>
        /// Returns the opengl IGraphicsContext associated with the current GameWindow.
        /// </summary>
        public IGraphicsContext Context
        {
            get
            {
                EnsureUndisposed();
                return glContext;
            }
        }

        #endregion

        #region 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.Graphics.OpenGL functions or properties.
        /// </summary>
        public bool IsExiting
        {
            get
            {
                EnsureUndisposed();
                return isExiting;
            }
        }

        #endregion

        #region Joysticks

        /// <summary>
        /// Gets a readonly IList containing all available OpenTK.Input.JoystickDevices.
        /// </summary>
        [Obsolete]
        public IList<JoystickDevice> Joysticks
        {
            get { return InputDriver.Joysticks; }
        }

        #endregion

        #region Keyboard

        /// <summary>
        /// Gets the primary Keyboard device, or null if no Keyboard exists.
        /// </summary>
        [Obsolete]
        public KeyboardDevice Keyboard
        {
            get { return InputDriver.Keyboard.Count > 0 ? InputDriver.Keyboard[0] : null; }
        }

        #endregion

        #region Mouse

        /// <summary>
        /// Gets the primary Mouse device, or null if no Mouse exists.
        /// </summary>
        [Obsolete]
        public MouseDevice Mouse
        {
            get { return InputDriver.Mouse.Count > 0 ? InputDriver.Mouse[0] : null; }
        }

        #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 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
            {
                EnsureUndisposed();
                if (render_period == 0.0)
                    return 1.0;
                return 1.0 / render_period;
            }
        }

        #endregion

        #region RenderPeriod

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

        #endregion

        #region RenderTime

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

        #endregion

        #region 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
            {
                EnsureUndisposed();
                if (TargetRenderPeriod == 0.0)
                    return 0.0;
                return 1.0 / TargetRenderPeriod;
            }
            set
            {
                EnsureUndisposed();
                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."); // TODO: Where is it actually performed?
            }
        }

        #endregion

        #region TargetRenderPeriod

        /// <summary>
        /// Gets or sets a double representing the target render period, in seconds.
        /// </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 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
            {
                EnsureUndisposed();
                return target_render_period;
            }
            set
            {
                EnsureUndisposed();
                if (value <= 0.005)
                {
                    target_render_period = 0.0;
                }
                else if (value <= 1.0)
                {
                    target_render_period = value;
                }
                else Debug.Print("Target render period clamped to 1.0 seconds.");
            }
        }

        #endregion

        #region 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
            {
                EnsureUndisposed();
                if (TargetUpdatePeriod == 0.0)
                    return 0.0;
                return 1.0 / TargetUpdatePeriod;
            }
            set
            {
                EnsureUndisposed();
                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."); // TODO: Where is it actually performed?
            }
        }

        #endregion

        #region 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
            {
                EnsureUndisposed();
                return target_update_period;
            }
            set
            {
                EnsureUndisposed();
                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."); // TODO: Where is it actually performed?
            }
        }

        #endregion

        #region UpdateFrequency

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

        #endregion

        #region UpdatePeriod

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

        #endregion

        #region UpdateTime

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

        #endregion

        #endregion

        #region VSync

        /// <summary>
        /// Gets or sets the VSyncMode.
        /// </summary>
        public VSyncMode VSync
        {
            get
            {
                EnsureUndisposed();
                GraphicsContext.Assert();
                return vsync;
            }
            set
            {
                EnsureUndisposed();
                GraphicsContext.Assert();
                Context.VSync = (vsync = value) != VSyncMode.Off;
            }
        }

        #endregion

        #endregion

        #region Events

        /// <summary>
        /// Occurs before the window is displayed for the first time.
        /// </summary>
        public event EventHandler<EventArgs> Load;

        /// <summary>
        /// Occurs when it is time to render a frame.
        /// </summary>
        public event EventHandler<FrameEventArgs> RenderFrame;

        /// <summary>
        /// Occurs before the window is destroyed.
        /// </summary>
        public event EventHandler<EventArgs> Unload;

        /// <summary>
        /// Occurs when it is time to update a frame.
        /// </summary>
        public event EventHandler<FrameEventArgs> UpdateFrame;

        #endregion

        #endregion

        #region --- Protected Members ---

        #region Dispose

        /// <summary>
        /// Override to add custom cleanup logic.
        /// </summary>
        /// <param name="manual">True, if this method was called by the application; false if this was called by the finalizer thread.</param>
        protected virtual void Dispose(bool manual) { }

        #endregion

        #region OnRenderFrame

        /// <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>
        protected virtual void OnRenderFrame(FrameEventArgs e) { }

        #endregion

        #region OnUpdateFrame

        /// <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>
        protected virtual void OnUpdateFrame(FrameEventArgs e) { }

        #endregion

        #region OnWindowInfoChanged

        /// <summary>
        /// Called when the WindowInfo for this GameWindow has changed.
        /// </summary>
        /// <param name="e">Not used.</param>
        protected virtual void OnWindowInfoChanged(EventArgs e) { }

        #endregion

        #endregion

        #region --- Assembly Members ---

        #region Methods

        #region ExitAsync

        // Gracefully exits the GameWindow. May be called from any thread.
        void ExitAsync()
        {
            HasMainLoop = false;
            isExiting = true;
            //UpdateFrame += delegate
            //{
            //    ExitInternal();
            //};
        }

        #endregion

        #endregion

        #region Properties

        #region HasMainLoop

        bool HasMainLoop
        {
            get { return hasMainLoop; }
            set { hasMainLoop = value; }
        }

        #endregion

        #endregion

        #endregion

        #region --- Private Members ---

        #region OnLoadInternal

        /// <summary>
        /// Raises the Load event, and calls the user's OnLoad override.
        /// </summary>
        /// <param name="e">The event data.</param>
        private void OnLoadInternal(EventArgs e)
        {
            OnResize(EventArgs.Empty);

            if (Load != null) Load(this, e);

            OnLoad(e);
        }

        #endregion

        #region OnRenderFrameInternal

        private void OnRenderFrameInternal(FrameEventArgs e)
        {
            EnsureUndisposed();

            if (!this.Exists || this.IsExiting) return; // TODO: Redundant because of EnsureUndisposed.

            if (RenderFrame != null) RenderFrame(this, e);

            OnRenderFrame(e);
        }

        #endregion

        #region OnUnloadInternal

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

            OnUnload(e);
        }

        #endregion

        #region OnUpdateFrameInternal

        private void OnUpdateFrameInternal(FrameEventArgs e)
        {
            EnsureUndisposed();

            if (!this.Exists || this.IsExiting) return; // TODO: Redundant because of EnsureUndisposed.

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

            OnUpdateFrame(e);
        }

        #endregion

        #region OnWindowInfoChangedInternal

        private void OnWindowInfoChangedInternal(EventArgs e)
        {
            glContext.MakeCurrent(WindowInfo);

            OnWindowInfoChanged(e);
        }

        #endregion

        #endregion

        ///// <summary>Finalizes unmanaged resources consumed by the GameWindow.</summary>
        //~GameWindow()
        //{
        //    Dispose(false);
        //    DisposeInternal(false);
        //}

    }

    #region public enum VSyncMode

    /// <summary>
    /// Enumerates 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
}