Problem draw SkyBox behind my sun - XNA

Question

I try to create a small and simple 3D games on XNA.

I recently started to add a skyBox after added a sun in my game with the sample by Microsoft here http://xbox.create.msdn.com/en-US/education/catalog/sample/lens_flare . The problem is , after add a skybox . My sun reacts strangely, it is no longer displayed. And occasionally, it bug. Appears and disappears repeatedly. Certainly because the sun is behind my skybox.

Youtube

I upload a video on YouTube of my problem too ;-) : https://www.youtube.com/watch?v=i8mdaibMqA4&feature=youtu.be

Problem identical

My problem is same as this : OcclusionQuery: how to ignore some objects?

Here is my file "SkyBox.fx"

    float4x4 WVP;
    float4 TextureColor;
    float AmountColorMix;


    float Depth;

    TextureCube tex;
    sampler cubeSampler = sampler_state {
        texture = <tex>;
        AddressU = CLAMP;
        AddressV = CLAMP;
    };

    struct VertexShaderInput
    {
        float4 Position : POSITION0;
    };

    struct VertexShaderOutput
    {
        float4 Position : POSITION0;
        float3 PosTex   : TEXCOORD0;
    };

    VertexShaderOutput VertexShaderFunction(VertexShaderInput input)
    {
        VertexShaderOutput output;
        output.Position = mul(input.Position, WVP).xyww;
        output.PosTex = input.Position;

        return output;
    }

    float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0
    {
        float4 color = texCUBE(cubeSampler,input.PosTex);

        return lerp(color, TextureColor, AmountColorMix);
    }


    technique Technique1
    {
        pass Pass1
        {
            CullMode = None;
            VertexShader = compile vs_3_0 VertexShaderFunction();
            PixelShader = compile ps_3_0 PixelShaderFunction();
        }
    }

Create and Draw the SkyBox (function)

        /* ********************************* */
        // Draw the SkyBox         
        /* ********************************* */
        #region DrawSky
        public void DrawSky()
        {
            arcadia.Game.GraphicsDevice.SetVertexBuffer(skyVertices);
            arcadia.Game.GraphicsDevice.Indices = skyIndices;

            skyEffect.Parameters["WVP"].SetValue(Matrix.CreateTranslation(arcadia.camera.Position) * arcadia.camera.View * arcadia.camera.Projection);
            skyEffect.Parameters["TextureColor"].SetValue(arcadia.lensFlare.ColorSun.ToVector4());
            skyEffect.Parameters["AmountColorMix"].SetValue(0.25f);
            skyEffect.CurrentTechnique.Passes[0].Apply();


            arcadia.Game.GraphicsDevice.DrawIndexedPrimitives(PrimitiveType.TriangleList, 0, 0, number_of_vertices, 0, number_of_indices / 3);

        }
        #endregion

        #region Creating a basic VertexBuffer
        void CreateCubeVertexBuffer()
        {
            Vector3[] cubeVertices = new Vector3[number_of_vertices];

            cubeVertices[0] = new Vector3(-1, -1, -1);
            cubeVertices[1] = new Vector3(-1, -1, 1);
            cubeVertices[2] = new Vector3(1, -1, 1);
            cubeVertices[3] = new Vector3(1, -1, -1);
            cubeVertices[4] = new Vector3(-1, 1, -1);
            cubeVertices[5] = new Vector3(-1, 1, 1);
            cubeVertices[6] = new Vector3(1, 1, 1);
            cubeVertices[7] = new Vector3(1, 1, -1);

            VertexDeclaration VertexPositionDeclaration = new VertexDeclaration
            (
                new VertexElement(0, VertexElementFormat.Vector3, VertexElementUsage.Position, 0)
            );

            skyVertices = new VertexBuffer(arcadia.Game.GraphicsDevice, VertexPositionDeclaration, number_of_vertices, BufferUsage.WriteOnly);
            skyVertices.SetData<Vector3>(cubeVertices);
        }
        #endregion

        #region Creating a basic IndexBuffer
        void CreateCubeIndexBuffer()
        {
            UInt16[] cubeIndices = new UInt16[number_of_indices];

            //bottom face
            cubeIndices[0] = 0;
            cubeIndices[1] = 2;
            cubeIndices[2] = 3;
            cubeIndices[3] = 0;
            cubeIndices[4] = 1;
            cubeIndices[5] = 2;

            //top face
            cubeIndices[6] = 4;
            cubeIndices[7] = 6;
            cubeIndices[8] = 5;
            cubeIndices[9] = 4;
            cubeIndices[10] = 7;
            cubeIndices[11] = 6;

            //front face
            cubeIndices[12] = 5;
            cubeIndices[13] = 2;
            cubeIndices[14] = 1;
            cubeIndices[15] = 5;
            cubeIndices[16] = 6;
            cubeIndices[17] = 2;

            //back face
            cubeIndices[18] = 0;
            cubeIndices[19] = 7;
            cubeIndices[20] = 4;
            cubeIndices[21] = 0;
            cubeIndices[22] = 3;
            cubeIndices[23] = 7;

            //left face
            cubeIndices[24] = 0;
            cubeIndices[25] = 4;
            cubeIndices[26] = 1;
            cubeIndices[27] = 1;
            cubeIndices[28] = 4;
            cubeIndices[29] = 5;

            //right face
            cubeIndices[30] = 2;
            cubeIndices[31] = 6;
            cubeIndices[32] = 3;
            cubeIndices[33] = 3;
            cubeIndices[34] = 6;
            cubeIndices[35] = 7;

            skyIndices = new IndexBuffer(arcadia.Game.GraphicsDevice, IndexElementSize.SixteenBits, number_of_indices, BufferUsage.WriteOnly);
            skyIndices.SetData<UInt16>(cubeIndices);

        }
        #endregion

Answer 1

Finally i solve and fix the problem by myself .

Add

GraphicsDevice.DepthStencilState = DepthStencilState.DepthRead;

before draw the skyBox

And Add

arcadia.Game.GraphicsDevice.DepthStencilState = DepthStencilState.Default;

after finish draw the skyBox

Full Code:

#region DrawSky
public void DrawSky()
{

    arcadia.Game.GraphicsDevice.DepthStencilState = DepthStencilState.DepthRead;

    arcadia.Game.GraphicsDevice.SetVertexBuffer(skyVertices);
    arcadia.Game.GraphicsDevice.Indices = skyIndices;

    skyEffect.Parameters["WVP"].SetValue(Matrix.CreateTranslation(arcadia.camera.Position) * arcadia.camera.View * arcadia.camera.Projection);
    skyEffect.Parameters["TextureColor"].SetValue(arcadia.lensFlare.ColorSun.ToVector4());
    skyEffect.Parameters["AmountColorMix"].SetValue(0.25f);
    skyEffect.CurrentTechnique.Passes[0].Apply();


    arcadia.Game.GraphicsDevice.DrawIndexedPrimitives(PrimitiveType.TriangleList, 0, 0, number_of_vertices, 0, number_of_indices / 3);


    arcadia.Game.GraphicsDevice.DepthStencilState = DepthStencilState.Default;
}
#endregion

Answer 2

One way of handling this is to modify the depth range in your viewport when drawing the skybox.

For XNA you would set both MinDepth and MaxDepth to 1, leaving the other members the same as your main viewport, like so:

Viewport.MinDepth = 1.0f;
Viewport.MaxDepth = 1.0f;

This will ensure that your skybox is always drawn to the back of the scene, and using this technique you don't need to worry about the skybox size at all: you could even draw it as a 10x10x10 cube around the view point and it would still work. This will also work well with any other kind of object you want to add in the sky (birds, etc).

Another way is to output a depth of 1.0f from your pixel shader, but that's generally not recommended as it can interfere with your GPU's early-Z optimizations.