wip Real-Time Body Physics (DirectX 11)

[Yotix]

Just thought I'd point out that in the first of the three videos on the download page, on the bottom left, the character's face is partly obscured by her boobs. 

 

 

Edited April 22 by Yotix

[Yotix]

Question: Will this work in POV mode at some point? If I press Shift-Tab while my character walks, the boob physics seem to stop.

[CPVC]

10 hours ago, Yotix said:

Just thought I'd point out that in the first of the three videos on the download page, on the bottom left, the character's face is partly obscured by her boobs. 

 

 

 

10 hours ago, Yotix said:

Question: Will this work in POV mode at some point? If I press Shift-Tab while my character walks, the boob physics seem to stop.

 

That's a known issue. Haven't found a way to detect when the game is rendering the sim for portraits yet and disable the physics.

 

It does work in point of view mode. If you're ever unsure whether it's working or not, open the GUI (F11), "Misc." -> "Test Linear (X|Y|Z)/Angular (X|Y)". Do linear testing if linear physics are enabled, angular if angular enabled. RTBP works on such a low level, that it's impossible to render a sim without it working, hence the distorted portraits.

[RyuK_]

On 4/21/2026 at 9:27 PM, CPVC said:

Another experimental release for you all.

 

RTBP v2.2~3 2026-04-21.zip 6.49 MB · 5 downloads

 

 

The settings ought to transfer over no problem. To use the linear breast physics exactly as they were the DLL you provided, make sure the breasts are set to use linear physics and enable the debug flag "testAltBreastPhysics8".

As for the font, I have changed that. Now that I think about it, it was a poor choice. Not everyone knows cursive. Really, I couldn't have picked a worse font. Whoops!

 

 

Other things:

 

The pivot point or the point the breasts rotate around is now calculated based on the geometry of the breasts, so for breasts that sag downward, the point should be located lower. This hasn't been tested extensively, so let me know if it works.

 

There is now an "Exaggerate Physics" option. When enabled, RTBP will attempt to exaggerate the physics in all the right ways to make for a more pleasant viewing experience. Currently, all this does it make it so upward moments are more powerful, making things more likely to bounce upward sharply, but more will be added in the future. Basically, by enabling this, you're telling RTBP you want less realistic, more fantasy-like physics. Let me know what you think of this and what other parts of the physics could be spiced up a notch.

 

https://streamable.com/34vsbk

(Left, "exaggerate" off. Right, on.)

 

Improved debugging? Looking at the logs people have been sending in and it seems like some of the issues I've been tracking have been fixed, but there's still recurring errors that need to be solved. The debugging has been improved somewhat to give me more informative stack traces.

I installed this experimental version and I noticed a new tab in the RTBP GUI named Sims, but there was only this message saying "RTBP is not tracking and sim meshes." and the physics are still not applied. I'm also including my log.

Log.txt

[alexlll]

When I launched the base game updated to the latest version without mods and with the latest version of RTBP installed, changing the resolution to 4K didn't launch the game. It wouldn't launch with any other resolution change. I had to uninstall RTBP, then change the resolution, then launch the game, and only then reinstall RTBP. Then everything worked as expected.

P.S.  "testAltBreastPhysics8" not work for mi.

Edited April 27 by alexlll

[CPVC]

On 4/26/2026 at 2:55 PM, RyuK_ said:

I installed this experimental version and I noticed a new tab in the RTBP GUI named Sims, but there was only this message saying "RTBP is not tracking and sim meshes." and the physics are still not applied. I'm also including my log.

Log.txt 5.9 kB · 1 download

 

I wish I could reproduce whatever issue you are having on my end. It would make it so much easier to tell what's gone wrong. I'll put together another DLL for you to test.

 

The "Sims" tab does list all the sim meshes being tracked and the associated simulators. If RTBP was working for you, you'd see them there. Thanks for pointing out the typo in "RTBP is not tracking and sim meshes." Wish the compiler would check for spelling mistakes in strings, too.

 

19 hours ago, alexlll said:

When I launched the base game updated to the latest version without mods and with the latest version of RTBP installed, changing the resolution to 4K didn't launch the game. It wouldn't launch with any other resolution change. I had to uninstall RTBP, then change the resolution, then launch the game, and only then reinstall RTBP. Then everything worked as expected.

P.S.  "testAltBreastPhysics8" not work for mi.

 

Huh, that's odd. Glad it started working in the end, though.

 

Make sure linear physics are enabled and disable angular.

 

 

With "testAltBreastPhysics8" debug flag enabled, the space the linear physics are calculated in should be the same as the version in the DLL you provided. If they aren't perfectly identical, the difference might be due to changes to the global constants that estimate the size of the world the sims exist in. If that's the case, then you might need to do a little tweaking to get things back to where you want.

[alexlll]

Perhaps we're misunderstanding each other. For me, working physics means that the Sim's chest moves when they move in CAS and in-game. Perhaps for you, working physics means that chests move during testing (test X, test Y, and test Z). Perhaps you don't need chest movement in-game and in CAS. These are completely different approaches. As I've written many times before, not all test physics work for me. Version 8 doesn't work for me under any settings, but it does work if I press test X, test Y, and test Z.

[Pankmasdred]

I have this issue where the mod will start and and body parts will lower but then they stay there and never move again. I test the different physics and only angular seem to be working, what might be causing this?

[CPVC]

17 hours ago, alexlll said:

Perhaps we're misunderstanding each other. For me, working physics means that the Sim's chest moves when they move in CAS and in-game. Perhaps for you, working physics means that chests move during testing (test X, test Y, and test Z). Perhaps you don't need chest movement in-game and in CAS. These are completely different approaches. As I've written many times before, not all test physics work for me. Version 8 doesn't work for me under any settings, but it does work if I press test X, test Y, and test Z.

 

No, the physics are meant to work in-game and in CAS and they do, for me at least. "testAltBreastPhysics8" works for me, too but with the default settings the movement can be a little subtle. Are you using heavily modified meshes? There is no guarantee that RTBP will work with custom content, whether it be meshes or body morphs.

 

2 hours ago, Pankmasdred said:

I have this issue where the mod will start and and body parts will lower but then they stay there and never move again. I test the different physics and only angular seem to be working, what might be causing this?

 

The "Test Linear (X|Y|Z)" buttons aren't working? Are linear physics enabled for the simulator you're testing on?

[Pankmasdred]

2 hours ago, CPVC said:

 

No, the physics are meant to work in-game and in CAS and they do, for me at least. "testAltBreastPhysics8" works for me, too but with the default settings the movement can be a little subtle. Are you using heavily modified meshes? There is no guarantee that RTBP will work with custom content, whether it be meshes or body morphs.

 

 

The "Test Linear (X|Y|Z)" buttons aren't working? Are linear physics enabled for the simulator you're testing on?

Yes! This is my log. It looks like the simulation isn't running.

Log.txt

[CPVC]

1 hour ago, Pankmasdred said:

Yes! This is my log. It looks like the simulation isn't running.

Log.txt 12.39 kB · 1 download

 

Oh, I see, you're running 2.2. You don't have the new GUI. In 2.2, linear physics have to be enabled with debug flags. Press "F11" to open the GUI, click the "Debug Flags" tab, find and check the flag that says "enableLinearPhysics" to enable linear physics.

 

After that the "Test Linear (X|Y|Z)" buttons should work. You can use linear physics at the same time as angular physics, or you can disable angular to just have linear. Check the debug flag "disableAngularPhysics" to do this.

 

In the next version, the GUI will look like this:

 

 

Linear, angular, and exaggeration can be enabled/disabled for each simulator.

[alexlll]

test sim.zip CPVC - Here is my Sim and RTBP dx9 settings. Unfortunately, I can't achieve something similar on the latest version of RTBP dx11.

Edited April 29 by alexlll

[CPVC]

3 hours ago, alexlll said:

test sim.zip CPVC - Here is my Sim and RTBP dx9 settings. Unfortunately, I can't achieve something similar on the latest version of RTBP dx11.

 

Oh, I see what's going on now. The physics you liked relied on some older super experimental angular physics code from back from before I had the correct breast bone locations. With your settings running in the new version, I see no movement at all, just like you said. In the DLL you sent, the old angular physics code must have been doing most of the heavy lifting.

 

That old code has been removed and porting it forward to the current version would be too difficult to maintain. I think you might just have to work with the new systems to find something you like. Sorry about that. 😞

[alexlll]

No big deal. Anyway, thank you for the great mod! I'll use the old version and test the new ones. I hope they'll be on par someday.

[kyojin77]

On 4/17/2026 at 10:12 AM, asdurgico said:

I'm also getting this error with CTD while travelling to other lots and when using the fashion autority mod (entering and exiting the modify in cas feature). I'm using the latest version

I got the same error using v2.2 2026-04-09 when starting a new game.
Any suggestions or fixes?
EDIT: Just tried v2.2~3 2026-04-21, got error too.

Edited April 30 by kyojin77
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[CPVC]

8 hours ago, kyojin77 said:

I got the same error using v2.2 2026-04-09 when starting a new game.
Any suggestions or fixes?
EDIT: Just tried v2.2~3 2026-04-21, got error too.

 

Send your log in and I'll take a peek at it. Hopefully I'll come up with a fix soon and make it availible in an experimental build.

[kyojin77]

6 hours ago, CPVC said:

 

Send your log in and I'll take a peek at it. Hopefully I'll come up with a fix soon and make it availible in an experimental build.

Hi, this is my RTBP log file.

Log.txt

[CPVC]

On 4/30/2026 at 10:13 PM, kyojin77 said:

Hi, this is my RTBP log file.

Log.txt 7.4 kB · 1 download

 

You're suffering from a common error that I don't have a fix for yet. The good news is that solving this issue is my number one priority right now. Fixing it will get RTBP working for you and a lot of other users.

[kyojin77]

9 hours ago, CPVC said:

 

You're suffering from a common error that I don't have a fix for yet. The good news is that solving this issue is my number one priority right now. Fixing it will get RTBP working for you and a lot of other users.

Damn. OK, thanks for the info. I guess I have to uninstall the mod for now. Good luck!

[CPVC]

11 hours ago, kyojin77 said:

Damn. OK, thanks for the info. I guess I have to uninstall the mod for now. Good luck!

 

Thanks. I'll do another proper release once I'm sure I've fixed it.

[CPVC]

I've gotten RTBP to build with Clang in MSVC compatibility mode. This is the compiler Google uses to build Chrome.

 

The cool thing about using Clang instead of MingW (the compiler I've been using to build RTBP up until now) is that Clang tries to be compatible with Microsoft's compiler, MSVC, and can link with Windows' standard library. This means that the resulting DLL is smaller, possibly more stable, and maybe even faster.

 

It's possible that this build could work for the users that have been having problems getting RTBP to work if the problem was with the compiler. Please try it out and let me know if it works. It is currently untested in Windows, but it's been running like a top for me in Linux. Absolutely no problems whatsoever.

 

A couple of changes between this experimental version and the last one:

 

* Reverted breasts center calculating back to fixed centers. This wasn't working for meshes with extra geometry on the breasts, like extravagant outfits or costumes.

 

* Shout out to patrons. As a special thank you to those who support RTBP, their names appear next to the logo upon starting the Sims 4 with RTBP installed. Thanks for the support.

 

* Sims tab. I think this was part of the last experimental release, but I didn't mention it. In the GUI, check out the "Sims" tab. You can mess with the simulators directly and watch their values change as the simulation runs. Click an address (0x123456) button to show the controls for that simulator. Check "Lock" to lock the values and drag the sliders to change values. Ctrl + click allows you to enter in a value directly.

 

Think that's it.

 

RTBP v2.2~4 2026-05-04 (Clang-CL).zip

 

Edited May 5 by CPVC

[APassingGhost]

On 5/5/2026 at 11:22 AM, CPVC said:

I've gotten RTBP to build with Clang in MSVC compatibility mode. This is the compiler Google uses to build Chrome.

 

The cool thing about using Clang instead of MingW (the compiler I've been using to build RTBP up until now) is that Clang tries to be compatible with Microsoft's compiler, MSVC, and can link with Windows' standard library. This means that the resulting DLL is smaller, possibly more stable, and maybe even faster.

 

It's possible that this build could work for the users that have been having problems getting RTBP to work if the problem was with the compiler. Please try it out and let me know if it works. It is currently untested in Windows, but it's been running like a top for me in Linux. Absolutely no problems whatsoever.

 

A couple of changes between this experimental version and the last one:

 

* Reverted breasts center calculating back to fixed centers. This wasn't working for meshes with extra geometry on the breasts, like extravagant outfits or costumes.

 

* Shout out to patrons. As a special thank you to those who support RTBP, their names appear next to the logo upon starting the Sims 4 with RTBP installed. Thanks for the support.

 

* Sims tab. I think this was part of the last experimental release, but I didn't mention it. In the GUI, check out the "Sims" tab. You can mess with the simulators directly and watch their values change as the simulation runs. Click an address (0x123456) button to show the controls for that simulator. Check "Lock" to lock the values and drag the sliders to change values. Ctrl + click allows you to enter in a value directly.

 

Think that's it.

 

RTBP v2.2~4 2026-05-04 (Clang-CL).zip 6.07 MB · 8 downloads

 

 

So uh

 

I wasn't having issues with the compiler? But I think this build might be causing my game to "stop responding"

 

I had a weird issue from Saturday morning til about this morning that I think only started when I replaced the 04-21 build with this one? And I only figured it when removing or replacing the d11 file stopped the freezing

 

I could be wrong - I'm still testing this myself, but I figured I'd give a heads up because no other mod seems to be causing the issue (removed all other mods to check)

 

If it's at all relevant, I'm a Windows user on the newest version of the game (as of writing, this is pre-May 12 patch)

[APassingGhost]

Update: Now that I've tested it with the older build, I can confirm that it is indeed the new Clang build of RTBP that's causing my issues

[jeno3]

Hi CPVC, 

 

I’ve attached a video. Please take a look at it. It consists solely of poses, but please observe what is happening there. Unfortunately, I’m not sure if the issue lies with the rig used by the pose creator. I’m just a bit confused, since the coordinate system remains fixed—or does it actually change depending on the Sim's orientation?

 

This is the  Test-Version (DLL) from 21.04.2026

 

Other

Breast_Gravity 2026-05-11 22-52-31-455.rar

[CPVC]

14 hours ago, APassingGhost said:

Update: Now that I've tested it with the older build, I can confirm that it is indeed the new Clang build of RTBP that's causing my issues

 

Hmmm, ok. Well, new compiler, new problems, I guess. Does your log file say anything when it freezes? Mind sharing it? It's possible a swich to Clang is a step in the wrong direction. I just wanted to see if it improved anything for those that were having problems and see if there were other benefits. In my testing, it seems to be more stable.

 

3 hours ago, jeno3 said:

Hi CPVC, 

 

I’ve attached a video. Please take a look at it. It consists solely of poses, but please observe what is happening there. Unfortunately, I’m not sure if the issue lies with the rig used by the pose creator. I’m just a bit confused, since the coordinate system remains fixed—or does it actually change depending on the Sim's orientation?

 

This is the  Test-Version (DLL) from 21.04.2026

 

Other

Breast_Gravity 2026-05-11 22-52-31-455.rar 3.84 MB · 0 downloads

 

It is fixed. Down should always be down regardless of orientation, but the coordinates I was using for linear physics are incorrect. I need to redo them with what I learned implementing angular physics. Try using the direct translation of the breast bones for linear physics calculations. Enable the debug flag "testAltBreastPhysics1". I'll get them working exactly as they should for the next release.