I was given the chance to write a blog post on this feature for socials, so I'll defer to that for specifics on implementation as well as additional visuals:
https://www.reddit.com/r/BattleAces/comments/1jm7cbz/dev_blog_fog_of_war/
That said, this was the result of a year and a half of effort that involved over a dozen people across multiple teams. I had the privilege and responsibility to gather the initial spec, consult as the core tech was being developed, assist with integration, improve both shadergraph and Houdini node chains to better work with the art, define feature and performance goals for completion, and deliver final look for this system as a whole.
Aside from a public facing blog post for social promotion, I also assisted in preparing a GDC proposal, wrote a patent application, and presented its development process as a case study for the engineering team.
Full effect in context
Overview with debug shader I authored to highlight simulation behavior
Slight adjustments to material and sim allowed for dramatically different presentation
Geometry driven initial density volume generated in Houdini before being converted to texture and sent to engine.
Post processing shader effects on top of fluid simulation