CBBE 3BA (3BBB)/Softbody: How to make breasts fall apart to either side when lying on back?

[LateOne]

Is there a configuration I can change or mod I can add to make the breasts of my character fall apart to either side when she's lying on her back? I use https://www.nexusmods.com/skyrimspecialedition/mods/30174.

 

Example (not my character):

 

Edited October 23, 2025 by LateOne
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[traison]

1. Make sure there's linear Y and linear X range.
2. Make sure there's gravity, and enough linear Y force to counter the Y axis damping and stiffness.
3. Add or increase linearYspreadforceX.
4. Negate the value for the right tit.

You can do the same for rotational forces on the Z axis with linearYrotationZ. Add these to all 6 tit bones, where the largest effect is on the 2nd bone.

 

There's some things to note here however:

1. I'm using a heavily customized CBPC build, but the instructions above should still work.
2. The public CBPC version does not negate Y axis forces while walking and moving, meaning if you want this effect your tits will also behave oddly while walking.
3. When in doggy position, or otherwise bending over, you'll get the opposite effect where the nips will touch eachother in the middle.

 

Edit: Actually I'm not sure if this is going to work. I think in public CBPC when horizontal, gravity actually points towards feet instead of down. Probably have to test this yourself.

Edited October 24, 2025 by traison

[traison]

Had a look at implementing this in my game too and I couldn't get it done with translated forces like I suggested above. I had to edit the CBPC code to get it done. Rotational Z force is the key, and it needs to be inverted depending on if the character is laying on their back or belly.

 

The "which way is up" value is in the rotation matrix at position 2-1:

float facingUpwards = obj->m_worldTransform.rot.data[2][1]; // (-1.0 ... 1.0)
// 0.95 is laying on back
// -0.95 is doggy

 

So to answer your question directly: That's either done with SMP, or it was "hardcoded" in the config to work specifically for that screenshot with a negative Z rotational value.

 

Edit: 2-1 might be wrong, as I'm getting unexpected results in the z rotational axis now. WIP. 2-0 is another potential candidate.

Edited October 24, 2025 by traison

[mircislav]

When installing 3BA (Acro) there is an option for boobs physics (install more gravity - there is explanation for every option) that does exactly what you want.

[traison]

Right, I got it working. The reason for the weird forces I was seeing was my own silly logic errors. 2-1 is where the up/down info is as originally stated, and rotational Z axis is the key to getting this to work. Use the up/down value to negate Z rotational.

 

So in other words, what @mircislav said is probably what you want to do, but my suspicion is that you will run into issues. Fixing those issues (like tits touching tips in doggy position) will require code edits, at least on CBPC. SMP is most likely no different in this regard, but it's been a long time since I used SMP for body physics; things may have changed.

 

If you want to DIY without code edits, set the left tit's Z rotational force to a negative value. Invert the value for the right side. Make sure it has enough room to move, and that the stiffness values allow it. May also want to check that there's no translational forces for X linear and Z rotational that would counter the motion, though as I already stated, these seemed to have little to no effect. I imagine this should still work, despite my CBPC having a rewritten gravity algorithm.

Edited October 25, 2025 by traison

[LateOne]

4 hours ago, traison said:

Right, I got it working. The reason for the weird forces I was seeing was my own silly logic errors. 2-1 is where the up/down info is as originally stated, and rotational Z axis is the key to getting this to work. Use the up/down value to negate Z rotational.

 

So in other words, what @mircislav said is probably what you want to do, but my suspicion is that you will run into issues. Fixing those issues (like tits touching tips in doggy position) will require code edits, at least on CBPC. SMP is most likely no different in this regard, but it's been a long time since I used SMP for body physics; things may have changed.

 

If you want to DIY without code edits, set the left tit's Z rotational force to a negative value. Invert the value for the right side. Make sure it has enough room to move, and that the stiffness values allow it. May also want to check that there's no translational forces for X linear and Z rotational that would counter the motion, though as I already stated, these seemed to have little to no effect. I imagine this should still work, despite my CBPC having a rewritten gravity algorithm.

Thanks I'll give it a shot