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Notes on Behavior Editing

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Since there's few information out there on editing Skyrim's Havok Behavior files, I would like to keep a record of my discoveries and important information thus far. 

Getting Started


1. Tools to read the files. Many awesome modders have made programs that can help you to edit and read.

  • hkxcmd: necessary to convert .hkx files to .xml and visa-versa.
  • convert-xml-hkx-kf: A UI for hkxcmd, makes it easier.
  • Skyrim Behavior Organizer: Somehwat detailed, used to look at values and flags
  • CondenseBehavior: barebones, used to quickly reference or find a section of the behavior files, where a modifier is used, etc.
  • An .xml editor. I use "XML Copy Editor", some prefer "Notepad++".

2. How to get new behaviors into the CK. Mostly concerned with actor behavior. Item animation behavior is much simpler and we already have Animated Dragon Wings mod as proof of concept.
EASY WAY: Copy existing behavior files into a new actor folder
CONS: Must duplicate animations resulting in a larger mod; behavior files may conflict with vanilla files depending on how much you alter them, affecting NPCS.
First, you have to make a new directory: data/meshes/actors/CUSTOMRACE
Then you extract animations and behaviors from an actor "Skyrim - Animations.bsa" and copy them into the CUSTOMRACE folder, and also extract the corresponding skeleton.nif from "- Meshes.bsa".

In the CK, you can change the paths to skeleton and behavior for a custom race for BOTH GENDERS. On the top of the window are options for changing male and female parameters. For the longest time this stumped me because I only changed the male behavior path and forgot the female one.
Finally, you make a new actor of your custom race and reload the .esp file. You can now go to Gameplay > Animations and fill in those animation events for your custom race.
IDEAL WAY: Custom-named, separate behavior files
CONS: Incomplete implementation! For experimental purposes only! Actor actions not working, AKA movement, jump, sneak, etc. will not register to the game. Unfortunately, until movement is figured out, if choosing this path you must send animation events through scripts or an external plugin! Recognition of Behavior names, Movement Types and iState animvariable is probably hardcoded!


3. Pre-Cache
According to nexus user Fore, the game uses a precache to cope with the high stress loads of animation blending, etc. It reads from the animationsetdatasinglefile.txt found within the Meshes folder. As a note, if one mod alters the asdsf file, any other mods, including FNIS, are incompatible. Making a patch is easy but tedious: copy the info from one mod into another. Since FNIS makes the biggest changes to this file, any smaller mods should be copied into the FNIS generated asdsf.
Getting CRC32 value of your animation filepath:


Delving into a Behavior Graph

1. Hardcoded events. The major problem with playable dragons was that the flying animations caused CTDs unless the player was AI driven, but then it's kind of pointless. Takeoff and landing animations were impossible UNLESS you edit the behavior file. I tried changing a lot of animation modifiers and even replaced the walking animation with the flying animation to confirm it wasn't the actual animation causing problems. The animations were fine, but when I checked player.getisflying with console commands, turns out the engine thought I was flying even with a completely different behavior file. I thought, "What if I replaced all the names of the animation events related to flying?" Walaah, no more CTDs. My character was also considered "not flying."

While I haven't tested, I'm guessing the events "moveStart" "shoutStart" "sneakStart" "sprintEnd" etc. are universal to all actors and if added in the behavior file, the game, in addition to playing the animations, will recognize and execute the action. Otherwise, it just plays animations.

Some events include:
idleChairSitting: makes the actor sit (sitting state 3). Actor can sit in midair; if you call reset event without the appropriate exit event, the actor will be stuck on the same z position.
idleChairGetup: exits sitting state (sitting state 0)
FlightCruising/Hovering/Perching: Only applicable to dragons. Calls engine code that makes player CTD or the camera go wack. I renamed/removed these event calls entirely to make dragons playable.
2_KillActor: kills actor who shares this behavior graph. For example, the human to dragon killmoves, where the dragon dies, this event is called in the dragon behavior graph.
weaponSwing: right hand weapon swing
weaponLeftSwing: left hand weapon swing
hit: hit registers

2. Hardcoded variables.
Some variables are also hardcoded. You can add them in a behavior file and they'll work automatically. Examples:

AimPitchCurrent: used for NPC's to aim their spells and when the player aims their bow; can be applied to other combat states like shown in Zartar's Character Behaviors Enhanced. 
iState: For dragons: 0 = default/ground, 1 = flying, 2 = hovering, 3 = perching (can check with Behavior Organizer tool). Setting this variable directly affects the Movement Type of the actor. Thus, default, flying and hovering can be changed in the CK's Movement Types. For humans, they have a lot of other states like BowDrawn, which again seems to be linked to MTs.
3. Definitions. Let's see, I'm not an expert but here's what I can gather.

Clip generator: links the animation files to the proper states and special effects.

Event: A cause. Events trigger certain states, like drawing out a weapon changes the state of the character to a combat stance.

Transition: Cause and effect. In a transition object, you can link events and states together. A "jump" event would bring the actor to a "jumping" state. There are still many flags whose effects are unknown.

  • wildcard transition: a state machine defines which event will cause transition FROM ANYWHERE in the graph to one of its states, or to a state in one of its children state machines. (credits to fore)

State: A condition that the actor is in, like sneaking state, combat state, walking, running, sprinting. You can have states within a state (nested state). Say there's a default state, the actor is simply standing around. Within that state, you can have a combat state, a running state, a jumping state, etc. Within the combat state, you can have 1h weapon state, 2h weapon state, spells. Within the jumping state, there's jumping forward, backwards, sideways, sprint-jumping. Pretty much every animation has its own state. 

Modifier: a special trait of this state. I believe it applies to all nested states too. (hkb = native to Havok Behavior. BS = Bethesda Softworks custom changes) Here are some examples of many:

hkbEvaluateExpressionModifier: Change variable values.
BSIsActiveModifier: I think it makes a boolean variable true as long as the graph is within this state.
hkbModifierGenerator: When you want to have more than one modifier, you use this which links to a list of modifiers.
hkbModifierList: Where you define at least one modifier.
hkbEventDrivenModifier: activates and/or deactivates another modifier with certain events.
hkbTwistModifier: alter rotation of bones on three axis, in the positive direction (1) or negative (-1).
BSTimerModifier: Sends an event after a specified amount of time. Useful for things like altering the falling animation after falling for a while, and/or to give a different landing animation after falling for x seconds.
BSLookAtModifier: Related to headtracking; probably needs a lot of tweaking to get it right for players, if at all.
BSDirectAtModifier: manipulate certain bones to follow the camera/LOS with variables AimPitchCurrent and AimHeadingCurrent (vanilla game does this for bows and NPC magic only)

4. Attack Data
I have limited info on this. It's questionable, but I believe it is possible to add new attacks to a race. Under the 'Attack Data' tab, there is a button "Update Events." Clicking it will update the window if new attack events are added to the behavior graph. "Display Event Data" is self explanatory, but it will show you if data is missing from an attack. The attack events are hardcoded, but there are many events. Theoretically you could add new attacks. For example, attackStart_Attack1 is a viable event, used for creature races but unused in NPCs.
Curiously, the dragon graph attack clips do not send the "hit, weaponswing, etc." events that clips in the humanoid graphs send. However, these events are defined in animationdatasinglefile.txt. The attack animations themselves do not contain any attack events, so it is safe to assume the game reads attack data through the behavior graph, some can be in animation annotations although it is not the case for human attacks, and finally adsf. I would not recommend editing adsf, so I assume behavior graph changes and animation annotations. But i have not actually implemented new attacks as there are more pressing issues.

Edited by Ceruulean, 26 November 2015 - 04:40 PM.



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In response to post #29804380.


In case, may be to early, still, this should be more videly spreed, as you say, information over behaviour files = :/.

Knowing then that some others have also made some progress, it could be time for a community wide gathering.

To be seen.

Thanks, of course.



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I can finally get custom named behaviors to stop giving me "cannot find root" error in the CK...
but there's still a problem:


EDIT: Ok, it's possible to add a new behavior file! Right click on a filepath, choose "Insert Sibling," find the .hkx file in the Behaviors folder and now you can add Action children. However.... if it's a custom behavior file, ActorActions don't register. Funny though, I can send animevents via console. The actor also plays the idle animation, the default state. Then there's more to the puzzle... it may be related to SpeedDataSingleFile.txt. With all these developments, I have updated the first post.

Edited by Ceruulean, 26 November 2015 - 01:01 AM.




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Failed...no one can crack this yet.
However...my custom weapon is working...with its behavior files
I'm still figure it out how to create custom races...still...no clues.
Perhaps, linking custom behavior in nif files may work.
This may require Custom race to work.

I'll try that later.

Edited by HanzSteiger, 17 October 2017 - 07:59 PM.

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