Vertex fog producing black artifacts

Question

I am rendering a textured model using the XNA BasicEffect. When I enable fog, the model outline is still visible as many small black dots when it should be "in the fog". Why is this happening?

Here is a minimal example showing my problem: (the ship model that this example uses is from the chase camera sample on this site — in case anyone wants to try it out ;))

public class Game1 : Microsoft.Xna.Framework.Game  
{  
    GraphicsDeviceManager graphics;  
    SpriteBatch spriteBatch;  

    Model model;  

    public Game1()  
    {  
        graphics = new GraphicsDeviceManager(this);  
        Content.RootDirectory = "Content";  
    }  

    protected override void LoadContent()  
    {  
        // Create a new SpriteBatch, which can be used to draw textures.  
        spriteBatch = new SpriteBatch(GraphicsDevice);  

        // TODO: use this.Content to load your game content here  
        model = Content.Load<Model>("ship");  
        foreach (ModelMesh mesh in model.Meshes)  
        {  
            foreach (BasicEffect be in mesh.Effects)  
            {  
                be.EnableDefaultLighting();  
                be.FogEnabled = true;  
                be.FogColor = Color.CornflowerBlue.ToVector3();  
                be.FogStart = 10;  
                be.FogEnd = 30;  
            }  
        }  
    }  

    protected override void Draw(GameTime gameTime)  
    {  
        GraphicsDevice.Clear(Color.CornflowerBlue);  

        // TODO: Add your drawing code here  
        model.Draw(Matrix.Identity * Matrix.CreateScale(0.01f) * Matrix.CreateRotationY(3 * MathHelper.PiOver4),  
            Matrix.CreateLookAt(new Vector3(0, 0, 30), Vector3.Zero, Vector3.Up),  
            Matrix.CreatePerspectiveFieldOfView(MathHelper.PiOver4, 16f/9f, 1, 100));  

        base.Draw(gameTime);  
    }  
}  

Answer 1

Texture contains dark & almost transparent pixels. Fog is internally controlled by alpha to support alpha blending with fog enabled.

You should remove alpha from the texture (or set it to 100% everywhere) if you intend to use the fixed function pipeline. If you have shaders in mesh effects, you can alternatively implement fog differently in those.