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Rules for BVH animations changed ?


Gaia Clary
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Hi;

I recently was testing to see if our long standing rules for exporting BVH really create valid animation files. However i found some oddities where the various "believes" on the web did not match with my finds. So i have collected a new rule set for BVH animations that seems to apply nowadays as far as i can tell. However i am not sure if this is totally correct or just works sometimes by chance. The new rules are here:

Rule 1: First frame of an animation defines the startlocation of the animation
Rule 2: First frame of an animation is not played (unless the animation has only one frame)
Rule 3: One-frame animations work (despite of rule 2)
Rule 4: A bone is only animated if animation values differ at least on 2 frames

Some more details are here:

https://blog.machinimatrix.org/2018/06/20/rules-for-exporting-bvh-animations/

Can someone acknowledge or dismiss this ruleset?

For Avastar users: the most recent daily build avastar-2.4-24 contains the new rule set so you could actually check if it works for your purposes.

thanks,

cheers,
Gaia

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6 minutes ago, Gaia Clary said:

Rule 1: First frame of an animation defines the startlocation of the animation
Rule 2: First frame of an animation is not played (unless the animation has only one frame)
Rule 3: One-frame animations work (despite of rule 2)
Rule 4: A bone is only animated if animation values differ at least on 2 frames

Those rules seem true, when I did some dabbling in Petite and RooU Animtions I found 1 and 4 effective, no idea how they were before I only started working on animations recently ... AFAIK you can also now also prune away part of the xml tree you do not want to animate (I think it was any child nodes that remain unmoved).

Edited by Fionalein
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17 hours ago, Gaia Clary said:

Rule 1: First frame of an animation defines the startlocation of the animation
Rule 2: First frame of an animation is not played (unless the animation has only one frame)

#1 is true

#2 the first frame of the animation seems to be triplicated and it's especially noticeable when looping

17 hours ago, Fionalein said:

Rule 3: One-frame animations work (despite of rule 2)
Rule 4: A bone is only animated if animation values differ at least on 2 frames

#3 they work because of #2 being triplicated

#4 uploader behavior in attempt to clean up the animation from excessive data, these 2 frames should trigger a rotation delta >= a specific value, dependent from animation length and FPS (the formula is unknown to me, couldn't find it in the viewer source code)

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1 hour ago, OptimoMaximo said:

On a side note, now that the internal format is available, what's the use of BVH anyway? why don't you dump it altogether, since it is so lossy after upload?

... because not everyone wants to buy software... duh 9_9

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@OptimoMaximo ok, i can see a bit better now how the BVH animations behave. This is my find as far as i understand it from some tests:

  1. The first frame is not played (only used as control frame, see Rule 1)
  2. The second frame is played 3 times
  3. Then each consecutive frame is played once.
  4. To get the in% and out% for a loop correct the triplation of the f1 frame needs to be considered in the calculation (see below)

So for a 3 frame animation (f1, f2, f3) with one prepended reference frame (rf), the animation plays like this:

(f1), (f1), (f1), (f2), (f3)

If you want to make a perfect loop over the animation (f1,f2,f3), then:

  1. set in to 50%
  2. set out to 100%

This setting would then play (f1), (f1), (f1), (f2), (f3), (f1), (f2), (f3), ...

ok, sooo we actually can do something in our software to help the BVH adicted :)

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2 hours ago, Fionalein said:

... because not everyone wants to buy software... duh

a bit out of place comment, i think: it's a software's feature that's being talked about, and the dropping of BVH was not meant for SL, but for said software.

DUH...

Edited by OptimoMaximo
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