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Thread: Bullet not working with Mocap?

  1. #31
    Eat your peas. Greenlaw's Avatar
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    Okay, I think your last couple of posts present a few clues. Are you trying to use bones to deform the collision object? If so, that's probably the issue.

    If I recall, an object deformed by bones can't be used as a collision object, at least not in the deforming state. If you need an object to be both a deforming object AND a collison object you need to scan an MDD of the object and then set that to be a Deforming Body. Then, you want to dial the settings for that object so that Bullet doesn't try to add other dynamic deformations to it. (There's an alternative method using DP MetaFit--it's faster because all the calculation is done upfront. However, because it calculates every time you open the scene, it can be slow to start.) It's been a long time since I tried this approach so I might be fuzzy on the details but I think that's it in a nutshell.

    Anyway, as mentioned above, I highly advise against doing it this way--this approach is very calculation/time intensive and really not worth the trouble. I HIGHLY recommend using proxy objects parented to the bones and setting them to be Kinematic Bodies. This is much easier to set up, it's a lot faster calculate, and in many situations it can more tweakable and predictable.

    To see this in action, here's a video I made a couple of years ago:



    In this early FiberFX-Bullet test, I have an animated bone chain with a sphere attached to each bone. Calculation is near realtime. If I had set this up using an actual deforming object under the carpet, it would probably take a long time to calculate--plus, it's a lot of extra work I don't care to do or really have time for.

    Continued...

  2. #32
    Eat your peas. Greenlaw's Avatar
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    ...continued.

    Here's a more relevant example:



    This was an early Mocap-FiberFX-Bullet test for our short film 'B2', currently in production. If you scrub to 00:51 of the video, you can see the Bullet setup for the hair. I believe the wig was just parented to the head bone, as was low-poly head, arms and shoulders objects for collision. As stated in the video, hair calculation time with collision was bout 12 minutes for 953 frame, and this was done on a fairly modest computer by today's standards.

    Hope this info helps.

    Sorry I didn't get that file uploaded last night--it just got too late. Will try to get it posted sometime today.

    G.

  3. #33
    Quote Originally Posted by prospector View Post
    Think I found problem, but not how to correct it.
    The collision object is not following main object when FBX is applied.
    Attachment 122263
    .....
    Hi,
    to use a deformed object (by bones, displacement or morphs) for collision in bullet you have to set the Type to "Deforming", not to "Kinematic". Also "Shape Retention" must be set to 100%, "Shape Lock" to Translation & Rotation, "Linear" and "Angular Stiffness" to 0 and "Volume Conservation" to 0. That should work.

    ciao
    Thomas
    Web: www.dieleinwandhelden.com

    I use two pieces of the three-piece application with mocap module.

  4. #34
    Eat your peas. Greenlaw's Avatar
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    Thomas, it seemed like when I tried that back in 11.5.x, while the item being deformed by bones did deform with Bullet, I couldn't get it to behave as a collision object. But maybe this was a bug at the time? I really should revisit this. TBH, I'm a little fuzzy on what I was using DP Metafit for back then--I think it was to deform a duplicate object that was used for the actual collision object, or something odd like that. When I have time, I really should go through my old notes using the latest version and see what Bullet behavior has changed since 11.5.x.

    In any case, as recently as last spring (11.6?), I found that using Deforming Bodies for collision was extremely slow--prohibitively so for the deadlines I typically face, which is why I recommended using proxies as Kinematics Bodies. Has this changed?

    Anyway, thanks for bringing that up--I'm curious to try it again as soon as I have time to experiment.

    G.

  5. #35
    Eat your peas. Greenlaw's Avatar
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    Oh, wait--I think I remember what I used DP Metafit for--it was probably to make the wig object stick to the deforming mesh while Bullet did its thing. From what I recall, it worked but I had switched to the Kinematic approach because it was faster to calculate and the result was fundamentally the same.

  6. #36
    dynamics...so much fun ;) prospector's Avatar
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    Are you trying to use bones to deform the collision object?
    I think so.
    It's parented to main body but is moved by bones of main object (ie; head turning and such)
    so probably yes.

    I have an animated bone chain with a sphere attached to each bone. Calculation is near realtime.
    So an object moved by bones is not deforming?
    Will try tho. but confusing.
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  7. #37
    Eat your peas. Greenlaw's Avatar
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    Quote Originally Posted by prospector View Post
    So an object moved by bones is not deforming?
    Will try tho. but confusing.
    In my past experience, yeah. According to Thomas' post maybe not.

    In any case, I typically don't bother with making the character's body mesh deformable for collision for reasons already laid out--IMO, it's just not worth the hassle and calculation time. There are easier, less CPU intensive ways to deal with this.

    G.

  8. #38
    dynamics...so much fun ;) prospector's Avatar
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    Well, I thought (cough cough)I was doing good for the first time using MMD anything.
    Never tried it before so everything was just a wild button toss

    I got her back into layout and under full animation without bones WOO HOOO!
    but alas, it was a short lived happiness.
    I then brought the wig in and parented it to the body..(Only choice I had)
    But it gets left behind just where it was loaded to.....crap

    Anyone see where I did a boo-boo in the send and receive
    Click image for larger version. 

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  9. #39
    Eat your peas. Greenlaw's Avatar
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    MDD by itself is not going to move an object that's parented to it. To do that, you'll need to either scan the body with ClothFX and use FX_MetaLink to move the parented wig, or use DP MetaFit to deform the object directly (DP MetaFit doesn't require ClothFX because it does it's own scanning on activation.)

    FWIW, I still recommend using proxy collision objects on bones. IMO, it's just a whole heckavu lot easier, faster and more predictable.

    G.

  10. #40
    To avoid misunderstandings:
    If you deform a object (regardless of whether you use bones, morphs, displacement or MDDs), you have to use "Deforming" mode in bullet to use it as a collision object. If you parent a object to a bone (not: "Use Bones From Object" in the bone properties) you use "Kinematic" mode in bullet.

    Click image for larger version. 

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    Deforming object:

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    Parented object:

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    Both works in LW 11.5 (Win64) and, as Greenlaw mentioned, the deforming object calculate a little bit slower.

    Another thing is, that you canīt use subdivided objects in bullet (you have to set the Subdivision Order to "After Displacement" or "Last") and of course bullet uses the cage geometrie which often could be to coarse...

    ciao
    Thomas
    Web: www.dieleinwandhelden.com

    I use two pieces of the three-piece application with mocap module.

  11. #41
    Eat your peas. Greenlaw's Avatar
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    Thanks for the clarification and illustrations Thomas!

    I must have misremembered how this worked because after seeing your test, I recalled creating a similar effect last year using Deforming collision (it was a creature breaking out an iceberg.) As demonstrated in your test above, Deforming collision did work in my scene but I had to switch to Kinematic mode because the calculation with Deforming was just too slow for the time I had available. The difference was quite dramatic too--a few minutes vs well over an hour for about two seconds of animation. I couldn't afford to keep re-running the sim if changes were requested so I abandoned the approach. Some might argue that the collision would have been more accurate using Deforming but I can't say it mattered much in this case.

    G.

  12. #42
    dynamics...so much fun ;) prospector's Avatar
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    trying seperate collision standins and so far things look promising. At least the hair is now following the FBX.
    So far so good.

    Thanks for all the pointers.

    For now
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