This is a directional fog of war system written for Xenko, feel free to use it directly or as an example. I am an amature so comments and/or PR's are welcomed. It consists of the following:

• When the project is launched there is a lengthy pause while the fog map is computed
• The fog map is a tile based visibility grid computed from customizable parameters
• Fog parameters are specifed in game studio in/on the FogOfWarSystem class
• There is a fog of war pre material overlaid on the map
• There is a fog of war post material attached to the camera which moves with the player
• A dual camera system, one perspective camera, one orthographic camera
• Orthographic camera renders to a texture in an isolated render group, this is used by the fog of war post material
• Perspective camera has two passes, one for the world, the second for the fog of war
• The fog of war pre material uses a shader which takes an array of floats which equate to opacity
• The fog of war post material is a result of the pre material pumped through a dedicated post effects pipeline
• Fog characteristics can be changed in the post effects settings through game studio (compositor)
• For smoother fog not only can you adjust post effects settings, but also the scale of tiles
• Game profiler is attached, control-shift-p, WASD to move around

+Runs quickly as it only uses table lookups and simple up/down logics.

Video can be found here

NOTE: Before the scene renders there is a lenghty delay while the fog map is generated. Ideally you would write the fog map/ visiblity data to a JSON or some other custom game data file and read it from disk to avoid the lengthy startup.

NOTE: This current project does not handle transparency of enemy units. This can be added easily by registering units with the fog of war system and doing a location lookup (truncation of current Pos) on the fog map, retrieving the Visibility value and pumping it through a transparency shader applied the enemy unit. An example of this can be seen in my XenkoFogOfWarPlus on the enemy unit shader. This way enemy units or characters will fade into visibility as fog is revealed.