Didn't most first person games have this automatically because of using the Quake engine due to their PVS system? It was used to reduce drawing overhead but also beneficial in not sending more data than needed and preserve bandwidth serversided.
AFAIK no they didn't, Valves engines are from the Quake lineage and still use PVS but they only added serverside fog-of-war to Counter Strike relatively recently in ~2015. As the Valorant article goes into, it's a harder problem than it appears because you need to allow the client some wiggle room to know an enemy in coming around a corner before the player sees them so that lag compensation and shadows work correctly (Valorant sidesteps the shadow issue by simply not having players cast shadows). Plus PVS is quite coarse so if you want precise culling you need a more computationally expensive solution.
This video compares Valves own fog-of-war implementation to the implementation used by FACEIT, a third party competitive matchmaking service, which shows there's a pretty wide range of trade-offs to be made. Valve went for conservative and fast, while FACEIT went for aggressive and (presumably) slow:
Valves implementation is better than nothing, it at least stops cheaters from knowing which direction the other team is going at the start of a round, but beyond that it doesn't stop them from knowing exactly where most enemies are standing around corners because the serverside visibility checks are so coarse.
Oh great video. Thanks for sharing. Surely the tick rate has to be lower on FACEIT as a consequence? Maybe this is why everyone in matchmaking would talk about it.
It's a matter of how aggressive is the fog of war and removal of irrelevant entities. Sometimes it's high, sometimes it's low. Too high, and people glitch into existence on high-latency connections. Too low, and you know exactly where people are far behind where you need to.
Many custom servers in games like CS enable a more aggressive version, in cases where you geographically will be close, so you can rule out high latency connections and have more aggressive fog of war.
I believe in the Quake case they made all the walls transparent so you could see everyone coming. Which means they weren’t doing much fog of war at the time.
Regarding the Quake engine and its evolutions (Q3, Call of duty, RTC Wolfenstein), the most common trick was to modify the rendering mode of all player entities so that they are drawn above everything else.
The engine has a flag that is mainly used to draw the player's weapon (which is rendered above the rest). Using this flag for players was the "engine compliant" way of making a wall hack.
