Xna shader issue

Question

Trying to make the glow effect in xna, but it does not show the glow or any changes at all. Also my black color is purple, not black, and I cannot change this:

        GraphicsDevice.Clear(Color.Black);
        GraphicsDevice.SetRenderTarget(bulletRenderTarget);
        spriteBatch.Begin();
        foreach (Bullet bullet in bulletList)
        {
            Texture2D bulletTexture = textures[bullet.bulletType];

            spriteBatch.Draw(
                bulletTexture,
                new Rectangle(
                    (int)bullet.position.X,
                    (int)bullet.position.Y,
                    bulletTexture.Width,
                    bulletTexture.Height
                ),
                null,
                Color.White,
                MathHelper.ToRadians(bullet.angle),
                new Vector2(
                    bulletTexture.Width / 2,
                    bulletTexture.Height / 2
                ),
                SpriteEffects.None,
                0
            );
        }
        spriteBatch.End();

        GraphicsDevice.SetRenderTarget(null);
        GraphicsDevice.Clear(Color.Black);
        postProcessEffect.CurrentTechnique = postProcessEffect.Techniques["Blur"];

        spriteBatch.Begin();
            spriteBatch.Draw(
            bulletRenderTarget,
            new Vector2(0, 0),
            Color.White
        );
        GraphicsDevice.BlendState = BlendState.Additive;
        foreach (EffectPass pass in postProcessEffect.CurrentTechnique.Passes)
        {
            pass.Apply();
            spriteBatch.Draw(
                bulletRenderTarget,
                new Vector2(0,0),
                Color.White
            );
        }

        DrawHud();
        foreach (BaseEntity entity in entityList)
        {
            entity.Draw(gameTime);
        }
        spriteBatch.End();

I'm just trying to make the bullets glow.

shader:

 float BlurDistance = 0.002f;
 sampler ColorMapSampler : register(s1);

 float4 PixelShaderFunction(float2 Tex: TEXCOORD0) : COLOR
 {
  float4 Color;

  // Get the texel from ColorMapSampler using a modified texture coordinate. This
  // gets the texels at the neighbour texels and adds it to Color.
  Color  = tex2D( ColorMapSampler, float2(Tex.x+BlurDistance, Tex.y+BlurDistance));
  Color += tex2D( ColorMapSampler, float2(Tex.x-BlurDistance, Tex.y-BlurDistance));
  Color += tex2D( ColorMapSampler, float2(Tex.x+BlurDistance, Tex.y-BlurDistance));
  Color += tex2D( ColorMapSampler, float2(Tex.x-BlurDistance, Tex.y+BlurDistance));
  // We need to devide the color with the amount of times we added
  // a color to it, in this case 4, to get the avg. color
  Color = Color / 4; 

  // returned the blurred color
  return Color;
 }

 technique Blur
 {
  pass Pass1
  {
   PixelShader = compile ps_2_0 PixelShaderFunction();
  }
 }

Answer 1

The reason it is purple is because you have

GraphicsDevice.Clear(Color.Black);
GraphicsDevice.SetRenderTarget(bulletRenderTarget);

which should be the other way around, therefore, changing it to

GraphicsDevice.SetRenderTarget(bulletRenderTarget);
GraphicsDevice.Clear(Color.Black);

fixes violet problem to fix shader change in fx file

sampler ColorMapSampler : register(s0);

And change yours spriteBatch.Begin()to

spriteBatch.Begin(SpriteSortMode.Immediate, null);

Additional Information:

s0 , ​​ spriteBatch.Draw, s1, GraphicsDevice :

GraphicsDevice.Textures[1] = bulletRenderTarget;

the SpriteSortMode.Immediate spriteBatch.Draw , , , , EffectPass.

, BlurDistance, , , , , .