Shader Fog

Have found out how to do fog in the shader so this means that you can now have fog in your XBox 360 games as well as your Windows based games.

As usual it is a matter of adding the right semantic and setting the correct renderstate in the shader.

So, the code.

Shader Model 1.1 - 2
In your Shader's vertex return structure, add the following

float Fog : FOG;

In your vertex shader set the fog you require:

Output.Fog = 1.0f - ( length( Input.Position - EyePosition) / 50.0f);

Note: This is an example you can generate this how ever you need to.

Now all you have to do is set the render state for fog, so in the top of your pass add this

FOGENABLE = (3);
FOGCOLOR = (float4(.5,.5,.5,1));

Where 3 is Linear fog and float4(.5,.5,.5,1) would be the color gray.

Shader Model 3
To get fog working on SM 3 and/or the XBox 360 is a little different

Remove ALL state settings in the technique.

Swap the FOG simantic for a TEXCOORD.

As the FOGCOLOR state has been removed, you need to
   calulate this in the shader per vertex lerp between the
   calculated color and the fog color based on the FOG
   TEXCOORD

For Example:

Out.Color = lerp(g_FogColor, color * ((In.Diffuse * g_MaterialDiffuseColor) * diffuse + g_MaterialAmbientColor), In.Fog);

Thanks to Leaf at XNA UK User Group and Jon Watte for your help with this I am sure this will help many others in there XNA development. Jon's shader also has the ability to specify the height of the fog and so giving a much richer fog effect, nice...

If you have any interest in the discussions we had then take a look here or the comments on this post.

Leaf has also put up an example of Jon's shader in action and you can find that here.