What is HDT-PE / HDT-SMP / BBP / TBBP / 3BBB?
Alright, considering a number of comments saying it's too difficult to select, I decided to write a short introduction what HDT is.
This isn't going to be hard to understand I believe. Read slowly and steadily if you don't understand what I am talking about.
So, where to begin? How about we talking about bbp and tbbp first. It's a very old thing but in case some of you guys even don't understand what they are, what these things do in your game, let's head to 'skeleton' first. I assume you already know about what skeleton.nif does. They are bones, literally. Without it, your character model can't do anything. What is worse, you will experience CTD right after installing a wrong, incompatible skeleton.nif. Your character model(CBBE, UNP, etc) needs an appropriate a skeleton.nif in order to move in the game. What does have to do with BBP or TBBP then? Well, in fact BBP, TBBP are just a mere part of the skeleton. Right now we only use XPMSE as a base skeleton so let's just call it XPMSE.
Actually BBP and TBBP aren't individual, seperate bones. BBP is a part of TBBP. They aren't something special. Those, pervy nerds, were so obssessed wtih breasts' movement that they started to add bones for breasts and butts. Just look at the name. BBP - Breast and Butt Physics.
Despite BBP, female body types only have one bone each for left and right breasts. People weren't satisfied with it because apparently BBP wasn't enough to make breasts natural. So people came up with an idea to attach additional bone to 'NPC L breast', 'NPC R breast'(These two bones are called BBP.) that would be called TBBP later which stands for Tender BBP(TBBP indicates 'NPC L breast', 'NPC R breast', 'NPC L breast01', 'NPC R breast01' in total 4 bones.). Funny, right? But they are what they are right now. They aren't something special. They are just a part of XPMSE bones. But we call it that way to make standards to categorize skeleton types.
Now we know that TBBP covers BBP and TBBP is a part of XPMSE. Then what is HDT-PE and HDT-SMP? What do they do?
We all know havok physics is quite essential when you make games. Even vanilla Skyrim has physics. But it didn't cover sexual movements, I mean breasts... So a very talented modder decided to make additional havok physics for it, HydrogensaysHDT is the name. HDT is just a username actually. Hydrogen just named a new physics system HDT-PE(HDT Physics Extension - https://www.nexusmods.com/skyrim/mods/53996). It was revolutionary because without HDT-PE, animators had no choice but to make all breasts, butts motions as well. But now, with HDT-PE, animators don't have to waste their time to animate breasts and butts. That's why you can see some of old animation mods' names starting with 'BBP / TBBP motions ~'.
After Hydrogen finishing HDT-PE project, she started a new ambitious project called HDT-SMP. This project, unfortunately, has been suspended semi-permenantly after she left Skyrim for some reason. No one knows neither where she's gone nor how to contact with her. It is known that it's almost abandoned for good. Despite the fact that the developement was canceled, SMP has proved quite resourceful because HDT-SMP allows physics way more realistic, natural compared to HDT-PE. Yes, HDT-SMP can be still utilized. It's an available source. But since she's gone, the optimization issue still remains. I gotta say it's not perfect. HDT-PE is so highly optimized that you can use it with few frame drops. But HDT-PE doesn't cover natural, more dynamic body movements. There are still pros and cons.
Okay, I get it. Now I understand what BBP / TBBP are and what is the difference between PE and SMP. But what about HDT-BBP, HDT-TBBP? Why mix them?
Let me remind you. TBBP is about bones. HDT is about physics. These two concepts are from different fields. I told that before hdt animators had to make breasts motions, right? Yes, they are non-hdt bones. You can still use non-hdt bones. Remember when you install XPMSE? There are two options. HDT or Fake Physics(non-hdt). If you select HDT bones, you can see how hdt physics work in your game.
Hold on... I still don't understand. You said HDT is about bones not about body meshes. But people keep saying HDT-BBP, HDT-TBBP.
You don't have to be confused. It just means body meshes with HDT name on it can only be used with hdt bones.
Then how are they different between HDT-T/BBP and Non-HDT-T/BBP?
Nothing. Totally nothing except for Havok-path embeded on it. Havok-path is required to link your body to physics settings. How far, how fast are they going to move, how heavy are they going to be? These sorts of values are needed when breasts are moving automatically. Therefore modders set up xml files in order to set the radius. So, without Havok-path, there is no way to load physics setting and your character's breasts, butts stay still not moving an inch. You may have heard of hdtPhysicsExtensionsDefaultBBP.xml before. It is one of them. It's not like there is a rule that the file names are fixed but tacitly there are several names used.
hdtPhysicsExtensionsDefaultBBP.xml - The very first basic setup for HDT-PE. It supports BBP bones only. It doesn't support TBBP bones.
hdt.xml - The extended version of hdtPhysicsExtensionsDefaultBBP.xml. It doesn't only supports TBBP bones but also other hdt bones as well like belly.
hdtvagina.xml - It manages vagina, anus. In addition, some modders tweak and add thigh, calves physics to this xml.
hdtFingers.xml - It handles fingers' collision physics.
hdt3BBB.xml - It handles 3BBB only.
At least one Havok-path is needed to make HDT-PE work in your game. Any mesh is okay as long as it contains Havok-path. That's why HavokObject(An invisible dummy mesh in order to link HDT-PE to your character.) has been used.
I think I'm following it. Then what is this 3BBB thing? It looks quite new to me.
Of course, it's new. 3BBB is a different bone set for breasts. As I told, TBBP has only two bones assigned to each breast. So I came up with an idea of making three bones for breasts for sexier, more natural movements. Keep in mind that both 3BBB and TBBP are just parts of XPMSE. They are just different bones compared to the relationship between BBP and TBBP.