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The SL Skeleton course


Gaia Clary
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Hi all;

I have been working on a course about the SL Skeleton and how to create Mesh attachments. Here is Lesson 1 (of 8):
               
http://blog.machinimatrix.org/lesson/sls-1/

I have tried to make the course as independent from any 3D tools as possible. However i added some practical tips for Blender users. The Lesson 1 also contains the course video.

The course is an ongoing work and i plan to add more information over time depending on the feedback that i get :matte-motes-sunglasses-1:


merry christmas

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Awesome first video Gaia! :D

I am really looking forward to the rest of the series. :)

Is there going to be a video on the Collision Bones?  That would be a very very interesting video.

I am in the process of updating my MayaStar and I can tell you figuring out how the Collision Bones respond to the sliders in SL was a big challenge.   Some of the changes are not contained in the avatar_lad.xml file like you think they would.  On those I had to just go by observations in SL and educated guesses.

Then there are the unexpected behaviors of some of the Collision Bones like the Upper and Lower Collision leg bones.  When you change your knee angle instead of just letting them be children to the "m" or Normal Bones LL decided they should rotate so the axis of the leg Collision Bones stay basically straight up and down.  While this is great for long dresses it is a major problem with pants and shoes if you have any other setting than 50 for the knee angle.  I dare say that more people are interested in shoes than long dresses.

Honestly LL should not have used the original Collision Bones at all.   A good number of them are at strange rotations and or scales not to mention some are offset a good distance from their "m" or Normal Bone counterpart which makes skinning harder since the initial binding process weights those vertices closest to the bone the most.

All of the standard  "m" bones or what I call Normal Bones have zero rotations and scales all set to 1 in the standard T-Pose.  This is pretty much an industry standard but some of original Collision Bones and some of the new ones like I said rotations and different scales.  This just adds to the complexity  of rigging Fitted Mesh unnecessary. 

In my opinion LL, if LL were going to use just the bone scaling method, it would have been better to have created a new category of bones called Fitted Mesh Bones and not use any of the original Collision Bones.  

To be perfectly honest my opinion is that the Mesh Deformer would have been a much better overall system than Fitted Mesh.  Way less work for content creators and it did respond to the morphs and physics since it deformered worn mesh by by using the avatars body to change the shape.  Even the facial and hand morphs worked.  Imagine the custom avatars that could have been made using it.

Oh well we can always hope LL will change their minds.  No reason both Fitted Mesh and the Mesh Deformer can't work side by side since they use completely different methods to deform mesh.  They did basically work side by side during the beta testing.

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Cathy Foil wrote:

Awesome first video Gaia!
:D

I am really looking forward to the rest of the series.
:)

Hi, Cathy;

Thank you for your answer and insight into your own travel into unknown spaces :matte-motes-smile: Regarding the series i have plans as follows:

 

  1. I have finished the 7 out of 8 lessons which cover what the course video introduces in much greater detail. This part is finished and ready available. It even contains a few references to other videos from my youtube channel which just fitted well to the lesson. But to be honest all these videos are public available from my channel. So you can find them there (in the 
    Playlist)
  2. I will add more (practical) information to the lessons over time and depending on the feedback that i get from users i will improve the lessons if necessary. I also plan to cut the lessons into smaller pieces because some have grown too big already (this tends to happen often as soon as you dig a bit deeper into the details :matte-motes-wink:
  3. I originally did not plan to add a special lesson about fitted mesh to the course because i have already explained all basic information about how the skeleton realy functions in the existing lessons (lesson 6 and 7 if i recall correctly). But meanwhile i have put it on my todo list because fitted mesh actually has a lot of practical pitfalls as you mention as well. So i will add a practical lesson to the course some time next year.
  4. I am not sure if i can add more videos. The one that i have published in the course took me almost 4 months to make it (as i can not work full time on them). Maybe i will add some with less gimicks...

When you change your knee angle instead of just letting them be children to the "m" or Normal Bones LL decided they should rotate so the axis of the leg Collision Bones stay basically straight up and down. 


Yes, the collision volumes have very odd scaling. However, the main issue is that the SL Avatar has been bound to the rig in a certain bind position. This is the main reason for the difference between the free Avatar used in Blender  (namely in avatar.blend and the Avatar workbench )  and what you see in SL (see in the course video). Our main issue with Blender is that it only supports binding to the Rest Position which is a realy annoying limitation.


Honestly LL should not have used the original Collision Bones at all.   A good number of them are at strange rotations and or scales not to mention some are offset a good distance from their "m" or Normal Bone counterpart which makes skinning harder since the initial binding process weights those vertices closest to the bone the most.

The collision Volume Bones have never been meant to be used for weighting. The reason why their Joints are at offsets from their corresponding parent bones is due to how they actually control the primitive collision Volumes which in turn are used for calculating when the avatar bounces into other objects/Avatars (the octahedrons which you can see in the SL Viewer when you enable "Display Collision Volumes" in the Debug Menu)

BTW the collision Volume Bones and all other bones of the SL Skeleton can be used for weighting because the skeletal animation technique allows a complete transformation matrix for each Joint (so that it can rotate, translate AND Scale) Luckily LL did not think about mesh 12 years ago. And that someone could want to add weights for arbitrary Bones of the Avatar. so they never added constraints to suppress such modifications. So it is NOT a bug that all of this is working.


All of the standard  "m" bones or what I call Normal Bones have zero rotations and scales all set to 1 in the standard T-Pose.  This is pretty much an industry standard but some of original Collision Bones and some of the new ones like I said rotations and different scales.  This just adds to the complexity  of rigging Fitted Mesh unnecessary. 

I do not know about industry standards. All i know is there is a difference between Rest Pose and Bind Pose. But i agree it would have been great if the SL Avatar meshes and the Collision Volumes had been bound to the Skeleton in Rest Pose (with all joints set to unity) IMHO this would have avoided a LOT of issues.


In my opinion LL, if LL were going to use just the bone scaling method, it would have been better to have created a new category of bones called Fitted Mesh Bones and not use any of the original Collision Bones.  

Another option would have been to put a bit of guesswork into how we could reuse the Mesh Morphing for custom meshes. That(!) would have solved all problems imho. Look at how nicely you can create attachments for the DAZ figures for example...


To be perfectly honest my opinion is that the Mesh Deformer would have been a much better overall system than Fitted Mesh.  Way less work for content creators and it did respond to the morphs and physics since it deformered worn mesh by by using the avatars body to change the shape.  Even the facial and hand morphs worked.  Imagine the custom avatars that could have been made using it.

I am not completely sure if the Mesh Deformer is the solution for all issues. But i have seen that it could solve a few of the major ones (like facial animation for example). I have no idea why exactly the Deformer was dropped and Collision Volume weighting was made official. maybe it was because the SL Avatar was prepared for the latter anyways...

Remind that we had collision Volume weighting (aka Liquid Mesh) for quiet a long time before LL decided to rename it to Fitted Mesh and add 5 extra bones to support that better.

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Pretty cool video! Maybe, you should do a video just about the special affects. I've played around alot with the skeleton, and made a few avatars with crazy skeletons, but I'd still want to take the course. Time is always the issue. I'm getting pulled in many directions these days. lol

I just want to add 1 things about Fitted Mesh. IMHO, the real problem with it is that is it locked to the avatar shape. If LL had just created the bones to ONLY deform the mesh, instead using existing bones and trying to match the avatar's shape with the collision bones, then it would work much better. If the meshes morphed from new bones, independent from the SL avatar's shape itself, then the new bones would have their own set of sliders, in the SL UI, and the wearer could adjust those sliders to make the clothing better fit. I really don't see why LL still can't do this.

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