c# - how to add fog to a model instantiated in Xna?

I work on a small XNA games. I generate a large map type voxel. a floor of 1000 cubic long by 1000 cubes wide. This is why I use the method "MODEL instancing" with hardware instancing to generate a large number of identical model ..

My problem is how to add fog to the cubic field? I know it is very easy to utiler fog with the class Microsoft.Xna.Framework.Graphics "BasicEffect". unfortunately i can not use this class because of the instancing model ...

I use Microsoft.Xna.Framework.Graphics "Effect" and does not contain a property "FogEnable, FogColor etc ..."

Do you have a solution to bring me to allow me to draw a fog on my models instantiated?

Thank you so much.

Here is my code that draws models

foreach (ModelMesh mesh in model.Meshes)
        {

            foreach (ModelMeshPart meshPart in mesh.MeshParts)

            {
                // Tell the GPU to read from both the model vertex buffer plus our instanceVertexBuffer.
                Game.GraphicsDevice.SetVertexBuffers(
                    new VertexBufferBinding(meshPart.VertexBuffer, meshPart.VertexOffset, 0),
                    new VertexBufferBinding(instanceVertexBuffer, 0, 1)
                );

                Game.GraphicsDevice.Indices = meshPart.IndexBuffer;



                // Set up the instance rendering effect.
                Effect effect = meshPart.Effect;
                //effect.CurrentTechnique = effect.Techniques["HardwareInstancing"];
                effect.Parameters["World"].SetValue(modelBones[mesh.ParentBone.Index]);
                effect.Parameters["View"].SetValue(view);
                effect.Parameters["Projection"].SetValue(projection);
                effect.Parameters["Texture"].SetValue(texture);


                // Draw all the instance copies in a single call.

                foreach (EffectPass pass in effect.CurrentTechnique.Passes)
                {
                    pass.Apply();

                    Game.GraphicsDevice.DrawInstancedPrimitives(PrimitiveType.TriangleList, 0, 0,
                                                           meshPart.NumVertices, meshPart.StartIndex,
                                                           meshPart.PrimitiveCount, instances.Length);
                }
            }


        }

My error if i use the technique (effect..Parameters["FogColor"]):

Answer

You need to add fog as parameters in a gpu shader file.

For example, set various parameters in your code:

float FOGNEAR = 250.0f;
float FOGFAR = 300.0f;

effect.Parameters["FogColor"].SetValue(Color.SkyBlue.ToVector4());

effect.Parameters["FogNear"].SetValue(FOGNEAR);
effect.Parameters["FogFar"].SetValue(FOGFAR);

And then, in the effect shader file that is chosen, use them such as:

float FogNear;
float FogFar;
float4 FogColor;

float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0
{

   float fog = saturate((input.Distance - FogNear) / (FogNear-FogFar));    

   return lerp(FogColor, color, fog);
}