Action Points
Action Points (short: AP) are a recharging resource, that denotes your character's ability to do things.
Shooting, Reloading, Using Items or Skills, Switching Gear. All those action require Action Points, that your character gains passively, depending on its Stats.
Without Action Points, you will not be able to do things like shooting, or healing yourself. And if you are in a negative amount of Action Points, you will additionally be restricted any movement, even though movement itself does not cost AP.
A character has 2 different types of AP Regeneration, which both work independently of each other, to top up your character's AP once more, after draining it.
Maximum Action Points
By default, your character has a maximum amount of 100 Action Points. This can rarely be altered - for example through the usage of drugs Afterburner Gum, or an artifact. Movement does not cost Action Points, it will however, lower the amount of Action Points you regain per second.
AP Regeneration
The first stat that governs how much AP you regain per second, is AP Regeneration. This value will be 10 for most cases, as it simply is the amount of your Action Points divided by 10. (So changing the amount of your maximum AP, will change the amount of AP Regeneration you have)
This type of regeneration, ONLY works when you are standing absolutely still and are not doing anything. It does not matter if you are in negative AP, or are knocked out. As long as your character is not performing any actions, including movement, you will get the AP per second it denotes.
AP+ Regeneration
Unlike normal AP Regeneration, AP+ Regeneration works even while moving and in some cases, even while shooting (Weapons with the Double Tap perk continue to gain AP from AP+ Regeneration, even while shooting). It is however, usually a much lower number, and heavily dependant on the stats you have.
By default, this value is:
Agiltiy thus plays a very big role in how much AP+ Regeneration you have. Though this number is much easier manipulated with the use of drugs, armor, perks like Action Boy and even traits like Bruiser.
Negative Action Points
Some actions can bring you into negative Action Points, while others can not. Knowing which actions do, is vital to success. As it helps to squeeze out a few more HP in vital moments. It is however equally as dangerous. As a character with negative Action Points will be robbed of any action, including movement! And thus will be a sitting duck, until his Action Points regenerate to at least 0.
