当透明图像覆盖图像时，应用模糊着色器会导致图像模糊

当透明图像覆盖图像时，我试图使其模糊，我只希望它模糊被覆盖的部分。因此，如果原始图像的一半没有重叠，那么这一半就不会模糊，但其余的则会模糊

未模糊-不重叠https://i.stack.imgur.com/joKzu.png

完全模糊-部分重叠https://i.stack.imgur.com/k8Tb7.png

Game1.cs

namespace NewShaderTutorial
{
    /// <summary>
    /// This is the main type for your game
    /// </summary>
    public class Game1 : Microsoft.Xna.Framework.Game
    {
        GraphicsDeviceManager graphics;
        SpriteBatch spriteBatch;
        Effect blur;
        Texture2D surge;
        Rectangle surgeRectangle;
        Texture2D bubble;
        Rectangle bubbleRectangle;
        private bool overlapping;
        public Game1()
        {
            graphics = new GraphicsDeviceManager(this);
            Content.RootDirectory = "Content";
        }
        /// <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
            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()
        {
            // Create a new SpriteBatch, which can be used to draw textures.
            spriteBatch = new SpriteBatch(GraphicsDevice);
            surge = Content.Load<Texture2D>("surge");
            surgeRectangle = new Rectangle(250, 250, surge.Width, surge.Height);
            bubble = Content.Load<Texture2D>("Bubble - Red");
            bubbleRectangle = new Rectangle(250, 250, bubble.Width, bubble.Height);
            blur = Content.Load<Effect>("blur");
            // 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();
            if (Keyboard.GetState().IsKeyDown(Keys.Left))
                bubbleRectangle.X--;
            if (Keyboard.GetState().IsKeyDown(Keys.Right))
                bubbleRectangle.X++;
            if (Keyboard.GetState().IsKeyDown(Keys.Up))
                bubbleRectangle.Y--;
            if (Keyboard.GetState().IsKeyDown(Keys.Down))
                bubbleRectangle.Y++;
            blur.Parameters["blur"].SetValue(0.015f);
            Overlapping();
            // TODO: Add your update logic here
            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);
            if (overlapping == true)
            {
                spriteBatch.Begin(0, null, null, null, null, blur);
                spriteBatch.Draw(surge, surgeRectangle, Color.White);
                spriteBatch.End();
                //     spriteBatch.Begin(0, null, null, null, null, blur);
                spriteBatch.Begin();
                spriteBatch.Draw(bubble, bubbleRectangle, Color.White);
                spriteBatch.End();
            }
            else
            {
                spriteBatch.Begin();
                spriteBatch.Draw(surge, surgeRectangle, Color.White);
                spriteBatch.Draw(bubble, bubbleRectangle, Color.White);
                spriteBatch.End();
            }
            // TODO: Add your drawing code here
            base.Draw(gameTime);
        }
        public void Overlapping()
        {
            float surgeDimensionX = surgeRectangle.X + surge.Width;
            float surgeDimensionY = surgeRectangle.Y + surge.Height;
            float bubbleDimensionX = bubbleRectangle.X + bubble.Width;
            float bubbleDimensionY = bubbleRectangle.Y + bubble.Height;
            if ((surgeRectangle.X >= (bubbleRectangle.X) && ((surgeRectangle.X <= (bubbleDimensionX))) && (surgeRectangle.Y >= (bubbleRectangle.Y)) && (surgeRectangle.Y <= (bubbleDimensionY))))
            {
                overlapping = true;
            }
            else
            {
                overlapping = false;
            }
            Console.WriteLine(overlapping);
        }
    }
}

着色器类

 float4x4 World; 
    float4x4 View; 
    float4x4 Projection; 
    // TODO: add effect parameters here. 
    sampler TextureSampler; 
    float blur = 0.0015; 
    struct PixelInput 
    { 
        float2 TexCoord : TEXCOORD0; 
    }; 
float4 PixelShaderFunction(PixelInput input) : COLOR0 
{ 
        float4 color = tex2D(TextureSampler, 
        float2(input.TexCoord.x+blur, input.TexCoord.y+blur)); 
    color += tex2D( TextureSampler, 
        float2(input.TexCoord.x-blur, input.TexCoord.y-blur)); 
    color += tex2D( TextureSampler, 
        float2(input.TexCoord.x+blur, input.TexCoord.y-blur)); 
    color += tex2D( TextureSampler, 
        float2(input.TexCoord.x-blur, input.TexCoord.y+blur)); 
    color = color / 4; 
        return color; 
} 

    technique Default 
    { 
        pass P0 
        { 
            // TODO: set renderstates here. 
            PixelShader = compile ps_2_0 PixelShaderFunction(); 
        } 
    } 

所以我想让部分重叠的部分只模糊重叠的部分，而不是整个精灵。解决这个问题的任何帮助或指导都将是伟大的。谢谢