How does the invis sphere work in ZDaemon?

[kuchitsu]

It seems to kind of make you really invisible (as opposed to the vanilla behavior) but not fully I think as sometimes some monsters still notice you? How does it work exactly? This would be very useful to know in some situations where you want to sneak by a scary cyberdemon or whatever.

[Gez]

I don't have the ZDaemon source, so the following is based on how it works in ZDoom. I just assume it's the same in ZDaemon.

If the player is over 128 map units away from the monster, and is moving slowly -- walking, not running -- then the monster will not detect the player. The monster also has an about 88% chance of failing to detect the player regardless. Keep in mind that this happens each time the monster is idly looking for a player (calling A_Look), which typically happens several times per second, so even if the probability of noticing the player is low on an individual roll, it's still high over a period of a few seconds.

And of course, a monster that has already acquired a target is not affected.

[kuchitsu]

Thanks, this explains a lot. So I literally have to turn off "always run"? Or can I just move in "short bursts"?

[Gez]

It's looking at the player velocity (aka momentum, in Doom code) right at the moment where the monster is looking, not at the average speed of the player over the last few tics. Short bursts wouldn't be a tactic unless you somehow manage to time them perfectly with the monster AI so as to always stop moving when they enter the next state of their idle loop...

The player's approximate speed has to be less than 5 units. Approximate because Doom doesn't use precise math for that kind of things, it just makes the sum of the absolute speed on both axes, and then subtract half of the slowest.

Basically you've got to move really slowly if you want to remain invisible.