Windows Phone Labyrinth

using System;
using FarseerPhysics.DebugViews;
using FarseerPhysics.Dynamics;
using FarseerPhysics.Dynamics.Joints;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Input;

namespace FarseerPhysics.SamplesFramework
{
    public class PhysicsGameScreen : GameScreen
    {
        public Camera2D Camera;
        protected DebugViewXNA DebugView;
        protected World World;

        private float _agentForce;
        private float _agentTorque;
        private FixedMouseJoint _fixedMouseJoint;
        private Body _userAgent;

        protected PhysicsGameScreen()
        {
            TransitionOnTime = TimeSpan.FromSeconds(0.75);
            TransitionOffTime = TimeSpan.FromSeconds(0.75);
            HasCursor = true;
            EnableCameraControl = true;
            _userAgent = null;
            World = null;
            Camera = null;
            DebugView = null;
        }

        public bool EnableCameraControl { get; set; }

        protected void SetUserAgent(Body agent, float force, float torque)
        {
            _userAgent = agent;
            _agentForce = force;
            _agentTorque = torque;
        }

        public override void LoadContent()
        {
            base.LoadContent();

            //We enable diagnostics to show get values for our performance counters.
            Settings.EnableDiagnostics = true;

            if (World == null)
            {
                World = new World(Vector2.Zero);
            }
            else
            {
                World.Clear();
            }

            if (DebugView == null)
            {
                DebugView = new DebugViewXNA(World);
                DebugView.RemoveFlags(DebugViewFlags.Shape);
                DebugView.RemoveFlags(DebugViewFlags.Joint);
                DebugView.DefaultShapeColor = Color.White;
                DebugView.SleepingShapeColor = Color.LightGray;
                DebugView.LoadContent(ScreenManager.GraphicsDevice, ScreenManager.Content);
            }

            if (Camera == null)
            {
                Camera = new Camera2D(ScreenManager.GraphicsDevice);
            }
            else
            {
                Camera.ResetCamera();
            }

            // Loading may take a while... so prevent the game from "catching up" once we finished loading
            ScreenManager.Game.ResetElapsedTime();
        }

        public override void Update(GameTime gameTime, bool otherScreenHasFocus, bool coveredByOtherScreen)
        {
            if (!coveredByOtherScreen && !otherScreenHasFocus)
            {
                // variable time step but never less then 30 Hz
                World.Step(Math.Min((float)gameTime.ElapsedGameTime.TotalSeconds, (1f / 30f)));
            }
            else
            {
                World.Step(0f);
            }
            Camera.Update(gameTime);
            base.Update(gameTime, otherScreenHasFocus, coveredByOtherScreen);
        }

        public override void HandleInput(InputHelper input, GameTime gameTime)
        {
            // Control debug view
            if (input.IsNewButtonPress(Buttons.Start))
            {
                EnableOrDisableFlag(DebugViewFlags.Shape);
                EnableOrDisableFlag(DebugViewFlags.DebugPanel);
                EnableOrDisableFlag(DebugViewFlags.PerformanceGraph);
                EnableOrDisableFlag(DebugViewFlags.Joint);
                EnableOrDisableFlag(DebugViewFlags.ContactPoints);
                EnableOrDisableFlag(DebugViewFlags.ContactNormals);
                EnableOrDisableFlag(DebugViewFlags.Controllers);
            }

            if (input.IsNewKeyPress(Keys.F1))
            {
                EnableOrDisableFlag(DebugViewFlags.Shape);
            }
            if (input.IsNewKeyPress(Keys.F2))
            {
                EnableOrDisableFlag(DebugViewFlags.DebugPanel);
                EnableOrDisableFlag(DebugViewFlags.PerformanceGraph);
            }
            if (input.IsNewKeyPress(Keys.F3))
            {
                EnableOrDisableFlag(DebugViewFlags.Joint);
            }
            if (input.IsNewKeyPress(Keys.F4))
            {
                EnableOrDisableFlag(DebugViewFlags.ContactPoints);
                EnableOrDisableFlag(DebugViewFlags.ContactNormals);
            }
            if (input.IsNewKeyPress(Keys.F5))
            {
                EnableOrDisableFlag(DebugViewFlags.PolygonPoints);
            }
            if (input.IsNewKeyPress(Keys.F6))
            {
                EnableOrDisableFlag(DebugViewFlags.Controllers);
            }
            if (input.IsNewKeyPress(Keys.F7))
            {
                EnableOrDisableFlag(DebugViewFlags.CenterOfMass);
            }
            if (input.IsNewKeyPress(Keys.F8))
            {
                EnableOrDisableFlag(DebugViewFlags.AABB);
            }

            if (input.IsNewButtonPress(Buttons.Back) || input.IsNewKeyPress(Keys.Escape))
            {
                ExitScreen();
            }

            if (HasCursor)
            {
                HandleCursor(input);
            }

            if (_userAgent != null)
            {
                HandleUserAgent(input);
            }

            if (EnableCameraControl)
            {
                HandleCamera(input, gameTime);
            }

            base.HandleInput(input, gameTime);
        }

        private void HandleCursor(InputHelper input)
        {
            Vector2 position = Camera.ConvertScreenToWorld(input.Cursor);

            if ((input.IsNewButtonPress(Buttons.A) ||
                 input.IsNewMouseButtonPress(MouseButtons.LeftButton)) &&
                _fixedMouseJoint == null)
            {
                Fixture savedFixture = World.TestPoint(position);
                if (savedFixture != null)
                {
                    Body body = savedFixture.Body;
                    _fixedMouseJoint = new FixedMouseJoint(body, position);
                    _fixedMouseJoint.MaxForce = 1000.0f * body.Mass;
                    World.AddJoint(_fixedMouseJoint);
                    body.Awake = true;
                }
            }

            if ((input.IsNewButtonRelease(Buttons.A) ||
                 input.IsNewMouseButtonRelease(MouseButtons.LeftButton)) &&
                _fixedMouseJoint != null)
            {
                World.RemoveJoint(_fixedMouseJoint);
                _fixedMouseJoint = null;
            }

            if (_fixedMouseJoint != null)
            {
                _fixedMouseJoint.WorldAnchorB = position;
            }
        }

        private void HandleCamera(InputHelper input, GameTime gameTime)
        {
            Vector2 camMove = Vector2.Zero;

            if (input.KeyboardState.IsKeyDown(Keys.Up))
            {
                camMove.Y -= 10f * (float)gameTime.ElapsedGameTime.TotalSeconds;
            }
            if (input.KeyboardState.IsKeyDown(Keys.Down))
            {
                camMove.Y += 10f * (float)gameTime.ElapsedGameTime.TotalSeconds;
            }
            if (input.KeyboardState.IsKeyDown(Keys.Left))
            {
                camMove.X -= 10f * (float)gameTime.ElapsedGameTime.TotalSeconds;
            }
            if (input.KeyboardState.IsKeyDown(Keys.Right))
            {
                camMove.X += 10f * (float)gameTime.ElapsedGameTime.TotalSeconds;
            }
            if (input.KeyboardState.IsKeyDown(Keys.PageUp))
            {
                Camera.Zoom += 5f * (float)gameTime.ElapsedGameTime.TotalSeconds * Camera.Zoom / 20f;
            }
            if (input.KeyboardState.IsKeyDown(Keys.PageDown))
            {
                Camera.Zoom -= 5f * (float)gameTime.ElapsedGameTime.TotalSeconds * Camera.Zoom / 20f;
            }
            if (camMove != Vector2.Zero)
            {
                Camera.MoveCamera(camMove);
            }
            if (input.IsNewKeyPress(Keys.Home))
            {
                Camera.ResetCamera();
            }
        }

        private void HandleUserAgent(InputHelper input)
        {
            Vector2 force = _agentForce * new Vector2(input.GamePadState.ThumbSticks.Right.X,
                                                      -input.GamePadState.ThumbSticks.Right.Y);
            float torque = _agentTorque * (input.GamePadState.Triggers.Right - input.GamePadState.Triggers.Left);

            _userAgent.ApplyForce(force);
            _userAgent.ApplyTorque(torque);

            float forceAmount = _agentForce * 0.6f;

            force = Vector2.Zero;
            torque = 0;

            if (input.KeyboardState.IsKeyDown(Keys.A))
            {
                force += new Vector2(-forceAmount, 0);
            }
            if (input.KeyboardState.IsKeyDown(Keys.S))
            {
                force += new Vector2(0, forceAmount);
            }
            if (input.KeyboardState.IsKeyDown(Keys.D))
            {
                force += new Vector2(forceAmount, 0);
            }
            if (input.KeyboardState.IsKeyDown(Keys.W))
            {
                force += new Vector2(0, -forceAmount);
            }
            if (input.KeyboardState.IsKeyDown(Keys.Q))
            {
                torque -= _agentTorque;
            }
            if (input.KeyboardState.IsKeyDown(Keys.E))
            {
                torque += _agentTorque;
            }

            _userAgent.ApplyForce(force);
            _userAgent.ApplyTorque(torque);
        }

        private void EnableOrDisableFlag(DebugViewFlags flag)
        {
            if ((DebugView.Flags & flag) == flag)
            {
                DebugView.RemoveFlags(flag);
            }
            else
            {
                DebugView.AppendFlags(flag);
            }
        }

        public override void Draw(GameTime gameTime)
        {
            Matrix projection = Camera.SimProjection;
            Matrix view = Camera.SimView;

            DebugView.RenderDebugData(ref projection, ref view);
            base.Draw(gameTime);
        }
    }
}