I was asked to write a short tutorial about jiggle bones so here goes. As usual I do not claim to be a master of the craft and shit I say may well be wrong. All opinions are just that and there are very probably tricks and techniques I don’t know about to making better of use of jiggle manipulations. I try to present these tutorials from the view of how I felt trying to learn the basics of how these features work and that is what they are designed to cover.
The final DMX can be found here.
Note that due to the nature of the topic this DMX will be of less help than the motion ones, because a lot of the information covered cannot be contained in a single dmx and is overwritten in the course of the tutorial; this one is of the final animation with baked jiggle bones + manual animation.
Helping us out today will be Elizabeth from Bioshock since she has the attributes we need. She was made by LordAardvark and can be downloaded from SFMLab here.
Read on for detail…
What are jiggle bones?
Jiggle bones refer to procedural bones in the model that will have their physics (how they move in the engine) determined by SFM itself. Not all models have jiggle bones, and if they don’t have them then there is nothing you can do about that other than de-compile the model, add them in a modelling program like blender and recompile it.
Because SFM wants to decide how these bones should move you cannot, to start with, modify them yourself. Because of this they are invisible on the model when you load it, you cannot see them or manipulate them. For our purposes (read: porn) the two places we see jiggles the most are breasts and butts and often hair is jiggled as well.
The amount of jiggle you will see is in response to the movement the model is performing. For example here we see Elizabeth turning from side to side slowly; not much shakin going on there.
Link to video
If we make the movement more extreme, we see more jiggle.
That doesn’t look comfortable, she is probably in for some major back issues later in life.
By default we do nothing to make this jiggle happen, it is entirely determined by SFM itself.
It is worth noting at this point that LordAardvark has done us a solid and Elizabeth has both normal breast bones and breast jiggle bones. This lets us move her breasts without having to bake her jiggle bones. However this is not common and for this tutorial we are mostly focusing on the jiggle bones and how they move, so we will ignore her added bones until the end.
Baking the bones
You may have already heard the term “baking procedural bones” or “baking the model” used before, if not it is the term used to describe “locking” the motion of our jiggle bones. Basically every time you play your animation in SFM, the program rebuilds the procedural motion of the jiggle bones fresh (this is similar to how locking works, but that’s for another time). But we will often reach a point where we don’t want SFM to build the motion anymore.
For example if we are making a loop we often want to bake the procedural bones to lock the motion so our loop loop’s cleanly. We also often want to bake procedural bones so we can make changes to the bones ourselves, for example we may not want a breast to jiggle around if it is being held.
To do this we need to right click on the model in the Animation Set Editor, select utilities and click on “Bake procedural bones”
This will lock the current motion of the jiggle bones, and even if we were to add more motion to our model, the jiggles will no longer change.
Because SFM is no longer rebuilding the motion all the time baking also tells SFM to return control of the models jiggle bones to us. We can now see our jiggle bones in our models bones list (they are usually called something_jiggle or jiggle_something, but not always) and are usually in the models “Unkown” tab.
Here we see Elizabeth’s breast and butt jiggle bones that have become visible after baking our model. We can now select our bones and manipulate them. If we select the bones and look at our graph editor we can see that the bones already have motion associated with them. This is the motion SFM has generated itself pre-bake.
Note: When we bake bones we will often see this initial extreme motion for the bone, located at the last place we started the animation before baking. Take the initial Elizabeth turning gif. If I had not baked the jiggles, or started it at the 0 second, I may get this initial wild bounce.
This happens because SFM needs to know what happened before in order to work out where the bone should move to and the start of our animation has no “before” to reference. SFM responds like any true computer program and has a minor freak out trying to determine the motion. This can manifest in our animations as an extreme initial bounce in our jiggle bones if we forget to account for this problem. Once we bake our bones we can see this initial motion in our graph:
This is part of why we want to bake our motion before we render our scenes. One good way to avoid this is to always leave 2 seconds or so at the start of your animation. This provides a buffer for the jiggle bone to “calm down” before our animation begins.
But I already baked them!
It is important to note that we are not doomed if we bake our bones and then want to re-enable our jiggle. At any time we can turn our jiggle bones back on by right clicking our model, going to utilities and selecting “Re-enable jiggle bones”. Once this is done we are returning control of the bones to SFM, so we will see that our jiggle bones will have vanished from our model bones list. Additionally it is important to remember that when you re-enable the procedural bones any changes you had made, or animations you had done that used the jiggle bones will be lost as SFM will rewrite their motion again.
As a final point to remember we cannot enable and disable jiggle bones individually. For this reason it is usual to make modifications to jiggle bones the last thing you do.
Changing motion
One point is that once we have our jiggle bones baked and can access them, we can use a feature of key framing to change the base line of our jiggle. You may have noticed that when animating if a bone only has one key frame, that key frame will change the entire line for that bone on our graph. This makes sense because without a reference point to move between (i.e. other key frames) SFM can only assume we mean that position to be constant. We can use this to our advantage with jiggle bone motion. If we provide a single key frame to the graph we can move the whole motion line to a new base point while keeping our motion.
Here we see our start line and with the jiggle bone selected. As expected the red line (Y axis) is the one with all the motion in it.
If we key frame and move on the red axis we can see the whole line moves with it, changing the root reference point for the jiggle.
The result in this instance, since we changed the base position of the right breast, will be wonky boobs in our animation, but wonky boobs with bounce..
We can use this trick to keep our motion while adjusting the base position, for example if she is on her back and with cans like that they would roll out to the side rather than point straight up. Another place this comes in very handy is adjusting hair. Often jiggled hair is multi boned and while we want jiggle we also want to be able to adjust its relative position, e.g. a pony tail always points to the ground. By using this type of technique we can change the root position of one bone while keeping our motion.
Adjusting across multiple key frames
Lastly we have a situation where we use multiple key frames. By its nature (you can tell because of the way it is) SFM has no real reference point when it creates jiggles. When we use a single key frame we can adjust the root point of the whole line, but SFM still doesn’t really know where in the world each position is. We use key frames to provide key points the motion needs to pass through, but the animation is really just moving point to point between key frames. When combined with jiggles this means that when we specify key frame points to pass through, SFM simply overwrites our jiggle motion; because we just told SFM to go from point to point and that takes precedence over existing movement. This means if we key frame our motion we lose our jiggle.
Putting it together
So now we have a reasonable idea of how jiggles work, how SFM is generating the motion, how we can override that motion, how we can change the relative position and what happens when we key frame our jiggle.
In general we want to let SFM do the jiggles on its own and bake them just before we render, that way we have the most up to date lines. Otherwise we run the risk of having added new motion that should have been accounted for after we bake. We can also use a combination of these aspects to do some neat things in our animations. For example if Elizabeth is holding one breast we don’t want that to bounce, while we want the other side to roam free.
Here we see that when we just lock her hand to her right breast we get our basic motion, but her breasts just bounce around.
We can use what we know now to fix this up. We baked our jiggles to lock motion, so we can now just go to the Unknown tab, and find the jiggle bones for Elizabeth’s right breast. Since she is holding her breast we don’t want this motion. We cant use a single key frame since that would just adjust the line, but by providing a point to point motion that is flat, we can remove all the jiggle. So here we just put a key frame at the start of our animation and copy it at the end, zeroing out the jiggle lines.
We can see we have zeroed out all our jiggle, and now when we render out our animation we have no motion in the right breast while keeping our left.
Remember here that we can still animate further, for example with Elizabeth LordAardvark has provided bones we can manipulate as well (even without these bones once we bake a models jiggles we can manipulate them directly).
In this last example, we locked her hand to her right breast and added some motion of our own to her right breast using her R Breast.root bone, since in reality her hand wouldn’t be stuck in place. Then just at the end, after all of our adjustments are done, we unlock her hand to split her breast and hand motion, move her hand away and add a little bit of manual bounce of our own. A rough version of this can be seen below.
Hopefully this has helped to answer some questions you may have had about jiggle bones. I am happy to answer any questions you have and if I have made any glaring mistakes feel free to let me know and I will make corrections. I am not sure what the next one will be but if you got this far maybe these are helping, so its a choice between Locking or fine tuning and finishing up our simple Tracer animation.