// 与上面获得小人的碰撞点类似
                Rectangle blockRectangle =
                    new Rectangle((int)blockPositions[i].X, (int)blockPositions[i].Y,
                    blockTexture.Width, blockTexture.Height);

// 如果小人与其中某一个碰撞纹理的碰撞点产生碰撞
                if (personRectangle.Intersects(blockRectangle))

 /// <summary>
    /// This is the main type for your game
    /// </summary>
    public class Game1 : Microsoft.Xna.Framework.Game
    {
        GraphicsDeviceManager graphics;
        SpriteBatch spriteBatch;
        Texture2D personTexture;    //小人纹理图像
        Texture2D blockTexture;     //撞击点纹理图像

// Person 
        Vector2 personPosition;     //小人2D坐标
        const int PersonMoveSpeed = 5;  //小人移动速度

// Blocks
        List<Vector2> blockPositions = new List<Vector2>(); //撞击点集合
        float BlockSpawnProbability = 0.1f;     //控制撞击点的下降个数
        const int BlockFallSpeed = 10;  //撞击点下降速度

Random random = new Random();
         
        bool personHit = false;         //是否产生碰撞
         
        Rectangle safeBounds; 
        const float SafeAreaPortion = 0.05f;
        Viewport viewport;  //获得当前窗口的宽高对象

public Game1()
        {
            graphics = new GraphicsDeviceManager(this);
            Content.RootDirectory = "Content"; 
            // Frame rate is 30 fps by default for Windows Phone.
            TargetElapsedTime = TimeSpan.FromTicks(333333);
        }

/// <summary>
        /// Allows the game to perform any initialization it needs to before starting to run.
        /// This is where it can query for any required services and load any non-graphic
        /// related content.  Calling base.Initialize will enumerate through any components
        /// and initialize them as well.
        /// </summary>
        protected override void Initialize()
        {
            // TODO: Add your initialization logic here
              viewport = graphics.GraphicsDevice.Viewport;
            safeBounds = new Rectangle(
                (int)(viewport.Width * SafeAreaPortion),    //40
                (int)(viewport.Height * SafeAreaPortion),   //24
                (int)(viewport.Width * (1 - 2 * SafeAreaPortion)),  //720
                (int)(viewport.Height * (1 - 2 * SafeAreaPortion)));    //432

// Start the player in the center along the bottom of the screen
            
            base.Initialize();
        }

/// <summary>
        /// LoadContent will be called once per game and is the place to load
        /// all of your content.
        /// </summary>
        protected override void LoadContent()
        { 
            spriteBatch = new SpriteBatch(GraphicsDevice);
            blockTexture = Content.Load<Texture2D>("Block");
            personTexture = Content.Load<Texture2D>("Person");
            personPosition.X = (safeBounds.Width - personTexture.Width) / 2;    //小人的坐标纵向在屏幕居中
            personPosition.Y = safeBounds.Height - personTexture.Height;    //小人的坐标竖向在屏幕底下居中
         
            // TODO: use this.Content to load your game content here
        }

/// <summary>
        /// UnloadContent will be called once per game and is the place to unload
        /// all content.
        /// </summary>
        protected override void UnloadContent()
        {
            // TODO: Unload any non ContentManager content here
        }

/// <summary>
        /// Allows the game to run logic such as updating the world,
        /// checking for collisions, gathering input, and playing audio.
        /// </summary>
        /// <param name="gameTime">Provides a snapshot of timing values.</param>
        protected override void Update(GameTime gameTime)
        {
            // Allows the game to exit
            if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
                this.Exit();

TouchCollection touch = TouchPanel.GetState();
            if (touch.Count>0)
            {
                if (touch[0].Position.X > viewport.Width / 2)
                {
                    personPosition.X += PersonMoveSpeed;
                }
                else
                {
                    personPosition.X -= PersonMoveSpeed;
                }
            }

double ran = random.NextDouble();
            // TODO: Add your update logic here
            if (ran < BlockSpawnProbability)    //随机循环Double 型如果随机的double 小于0.01f这样做是避免产生的撞击 点太多
            { 
                float x = (float)random.NextDouble() *//在屏幕随机出现 
                    (graphics.GraphicsDevice.Viewport.Width - blockTexture.Width);//为了不超出屏幕 
                Vector2 v = new Vector2(x, 1);
                blockPositions.Add(v);
            }

// 获得小人的磁撞大小和碰撞的地点 
            //公式为：得到小人所在的x、y 地点，然后在那个x、y点的区域高宽
            Rectangle personRectangle =
                new Rectangle((int)personPosition.X, (int)personPosition.Y,
                personTexture.Width, personTexture.Height);

// Update each block
            personHit = false;  //默认为不碰撞状态
            for (int i = 0; i < blockPositions.Count; i++)  //循环所有在集合里面的碰撞纹理
            {
                // 使里面的所有元素全部下降
                blockPositions[i] =
                    new Vector2(blockPositions[i].X,    //X坐标不变
                                blockPositions[i].Y + BlockFallSpeed);  //竖坐标为当前的Y座标每次加上下降的速度常量

// 与上面获得小人的碰撞点类似
                Rectangle blockRectangle =
                    new Rectangle((int)blockPositions[i].X, (int)blockPositions[i].Y,
                    blockTexture.Width, blockTexture.Height);

// 如果小人与其中某一个碰撞纹理的碰撞点产生碰撞
                if (personRectangle.Intersects(blockRectangle))
                    personHit = true;   //这时的碰撞检测将生效

// 如果有碰撞纹理超屏幕
                if (blockPositions[i].Y > graphics.GraphicsDevice.Viewport.Height)
                {   
                    //从集合里面移出该碰撞点
                    blockPositions.RemoveAt(i);
                     
                    //当删除了其中一个碰撞点时，下一个碰撞点的索引将跟当前移除的碰撞点是一样的，所以循环变量自动减1 
                    i--;
                }
            }
            base.Update(gameTime);
        }

/// <summary>
        /// This is called when the game should draw itself.
        /// </summary>
        /// <param name="gameTime">Provides a snapshot of timing values.</param>
        protected override void Draw(GameTime gameTime)
        {
            GraphicsDevice.Clear(Color.CornflowerBlue);
            GraphicsDevice device = graphics.GraphicsDevice;
            // TODO: Add your drawing code here
            if (personHit)  //当产生碰撞
            {
                device.Clear(Color.Red);
            }
            else
            {
                device.Clear(Color.CornflowerBlue);
            }

spriteBatch.Begin();

// Draw person
            spriteBatch.Draw(personTexture, personPosition, Color.White);

// Draw blocks
            foreach (Vector2 blockPosition in blockPositions)
                spriteBatch.Draw(blockTexture, blockPosition, Color.White);

spriteBatch.End();

base.Draw(gameTime);
        }