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![](https://lemmy.ml/pictrs/image/8nN0qtLEOJ.png)
There are many ways of doing this. I know the source engine uses visboxes, which are calculated once at map compile time. It takes a while to compile, but it means that clients can use the pre-compiled data to calculate parts of the map that are visible and the server can use them to determine what the player can see at a given time. I’m not sure whether it does that or not, but it would make sense to use that data.
That would also explain why Aldi in the UK also has these while other stores don’t.