All My Children Are Digital

1.       Background and in-game mechanics

The way TS4 handles different body shapes and clothes in animations (for example, in order to avoid clipping) is basically by putting markers (“slots”) on the surface of a sims body that can be then used as (IK) targets with the in-game IK system.

As you probably know, IK (Inverse Kinematics) – as opposed to the default FK (Forward Kinematics) – is a set-up where bones in a chain are influenced backwards. So, for example, when you move a hand, the arm will follow.

In a similar way, what in-game IK does, is assigning a bone or slot to animate relative to. For example, if your sim is posed with hands on the hips, you can assign the hands to the hips slot and the game will then process the pose/animation and perform IK in real time to change the position of the arms and hands relative to the hips.

Note that there are limitations to this system, though, as only hands, feet and the root bind can procedurally target other bones/slots.

You can find an article that provides some additional background information here: https://simsvip.com/2014/08/20/community-blog-the-sims-4-animations/

2.       Using the feature in custom poses/animations

Per default, when you make custom poses/animations with Blender and S4S, the relevant information that the game requires to apply in-game IK is not included. And so, you will notice that while a pose might look good with the base rig in Blender, it might not fit other sims with a different shape in game, in particular causing clipping.

You can use TS4 SimRipper to fine-tune a pose for a certain sim, but this might not be the solution you’re looking for, if you share your poses and/or want them to be compatible with different kinds of sims.

The animation tools now include a feature that makes it possible to use in-game IK with custom poses/animation as described in part 1.

Disclaimer:

The animation tools are in development and subject to change.

Currently TS4 SimRipper sims are not properly supported (although imo for the purpose of the task, it doesn't make much sense to use them.)

As you can see in the comparison below, there might be some accuracy loss for the flexibility gained. (The position of the arms in the version without IK targets matches exactly the pose I made in Blender but doesn't work at all for the heavier sim causing extreme clipping. At the same time, the version with IK targets deviates a bit from the pose I made, but works for any sim.)

Below a short guide on how to set it up with the example pose I made.

1)      You can download the tools HERE. Make sure to check the installation guide and tutorials in the wiki tab for the basics. (Note: The tools were originally made for Blender 3.0 but also support newer versions, in particular Blender 3.3.)

Some additional tips for poses in another post of mine HERE.

After you set up the tools in Blender and have made your pose:

2)      Go to the S4AnimTools panel. Fill out rig name, clip splits and clip name as described in the tutorials linked above (also make sure to select “Allow Jaw Animation”).

3)      Find & click “Create World IK channels”. 

This will create 5 IK channels for the afore mentioned hands, feet and b_ROOT_bind bone. You can also add channels either by cloning the existing ones or clicking “Create World IK channels” again. To get rid of unwanted channels click “Delete”.

4)      Set up the targeted bones/slots based on the type of pose you made.

In my example, I created a pose where a sim has the left hand on the hip, and the right hand close to the thigh. Therefore, I added IK channels targeting the “b__L_frontBellyTarget_slot” and “b__R_ThighFrontTarget_slot”.

The slots are marked blue in the picture below. Note that the slots are hidden by default – I made them visible for the picture. Tip: You can unhide all bones/slots available by pressing Alt+H. But I recommend doing this on a separate rig/in another blend file or undo it directly afterwards as you don’t want all these (for the most part irrelevant) bones/slots blocking your view.

5)      Each IK channel should (also) target b_ROOT of the rig to ensure it’s working properly according to pancake (though in my first test using Andrews pose player it seemed to also work without, so might be only a restriction for poses/animations that are played via interactions in game, but I can’t be sure.)

The bones are marked green in the picture below.

6)      The start and end frame is set according to the length of the pose/animation (I want to use the pose as a CAS trait pose and set the duration to 150 frames = 5 seconds), so except for the b_ROOT target for hands where the end frame is set to 0 in my example, as they are also targeting the slots “b__L_frontBellyTarget_slot” and “b__R_ThighFrontTarget_slot” during the animation.

7)      Bake the animation by pressing “Bake IK”.

8)      Export the clip and create a package with your pose as described in the linked tutorials above.