@Override
    protected void initFilter(AssetManager manager, RenderManager renderManager, ViewPort vp, int w, int h) {
        material = new Material(manager, "Common/MatDefs/Post/Fog.j3md");
        material.setColor("FogColor", fogColor);
        material.setFloat("FogDensity", fogDensity);
        material.setFloat("FogDistance", fogDistance);
    }
Create a fog filter 
@param fogColor the color of the fog (default is white)
@param fogDensity the density of the fog (default is 0.7)
@param fogDistance the distance of the fog (default is 1000)
jme3-effects/src/main/java/com/jme3/post/filters/FogFilter.java