Fixing problems with IPO driven bones

Animation tools, character animation, non linear animation

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tron_thomas
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Joined: Thu Jan 13, 2005 6:20 am

Fixing problems with IPO driven bones

Post by tron_thomas »

I have been working with trying to do some character animation with Blender, and I'm convinced there are bugs using the new driven IPO feature with armature bones.

I suspect this is a major problem that will not be addressed in the next release of Blender as the problem still exists in the latest release candidate.

I would very much like to see this problem address. As a software developer, I am willing to spend some time to look into the problem and try to fix it myself, or help someone else if an effort has already been started. It would be extremely helpful if I could get the guidance and direction on how to go about doing this.

What is the best way for me to get in touch with people that would have knowlege about how this feature of Blender is implemented?

aligorith
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Joined: Sun Dec 05, 2004 3:40 am
Location: Chch, NZ

Post by aligorith »

Any potential bugs you could name/describe?

Aligorith

tron_thomas
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Joined: Thu Jan 13, 2005 6:20 am

Post by tron_thomas »

I cannot cite anything specific at this time. The setup I'm using in somewhat complicated by the number of elements involved. It is based on a character animation tutorial explained in "Learning Maya 5 | Fundamentals".

The armature system is using inverse kinematic chains, locked track contraints, and driven IPO's. These elements are used to animate the legs and feet of a character. It is hard to determine what is at fault here. I'm not sure if it is a indivual component or an interaction between some or all of them.

To describe what is going on, I've been having a problem where the leg of the characters would pop at the knee. I tried to eliminate this popping by adjusting a driver object that was supposed to affect the roll of the foot. I wanted the foot to roll upward more so that leg would stay bent.

I would key frame this adjustment, and I'd still have the popping problem. What made it really diffcult to understand this problem and how to fix things was the fact that when I scrubbed the animation, I would see different result based on whether I scrubbed forward or backward. Seeing different results made thing very confusing. It was hard to know what to change and whether the change would work correctly.

When I scrubbed forward, it looked as though my adjustments didn't have much of an effect. When scrubbing the animation backward it looked more like how I had tried to animate the leg.

Even scrubbing backwards wasn't completely reliable because when I scrubbed all the way to the first frame the character would not be in the correct pose. The feet would be rotated incorrectly. This would also happen when I clicked the "Skip to Start frame" button on the the Timeline window. I foudn I had to click on that button twice to get the feet in the proper pose.

As I said, all of this behavior makes things confusing and frustrating when trying to fix a problem with the animation, and this is the problem I want to fix.

aligorith
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Joined: Sun Dec 05, 2004 3:40 am
Location: Chch, NZ

Post by aligorith »

When you say popping, are you meaning that the knee flips to a position that is totally opposite what it was before? If so, have you got any rotation limits on the joints in the armature? Some settings on the bones in the leg might fix this.

As for the lagging issue. I remember reading a bug report about something like this. I can't remember whether it has been fixed though.

Aligorith

tron_thomas
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Joined: Thu Jan 13, 2005 6:20 am

Post by tron_thomas »

The popping action had to with abrupt movement of the leg. It would straighten out and the bend again in a quick motion that actually be painful to someone walking that way in real life. I was trying to get a more natural realistic motion with the leg.

I don't think anything has been fixed concerning this because the release candidate seems to behave the exact same way.

Who would be good to talk to about looking into fixing this. As I said, I'd be willing to help out with this development. I've already fixed a problem in source code having to do with getting vertex weights from the Python scripting API.

I've looked at the armature code in the past and it has been very difficult to understand. Digging into this is not something that I would like to tackle by myself.

mstram
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Joined: Wed Apr 26, 2006 8:48 pm
Location: Toronto

Post by mstram »

Hmm, this might be related to this bug that I just posted

http://projects.blender.org/tracker/ind ... 9&atid=125

Mike

tron_thomas
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Joined: Thu Jan 13, 2005 6:20 am

Post by tron_thomas »

I don't know if this is the same problem or not. I did not evaluate the rig to see how its behaving. The problem I'm having is kind of subtle. For the most part the features work just fine. It's when fine tuning is needed that things become difficult.

Anyway, the end effect here is that the problem has not received much attention so far since it most likely won't be fixed in version 2.42.

I feel this problem needs to be fixed for me to really make progress with what I'm trying to do. Since I'm basically stuck, until this is addressed I'm willing to dedicate effort toward fixing this problem.

I would much prefer not to have to tackle this on my own as I have seen some of the armature code, and it was difficult to understand. I'd like to know where I could get some help with this or offer help to someone who may already be looking into this.

LetterRip
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Joined: Thu Mar 25, 2004 7:03 am

Post by LetterRip »

you might want to post the blend file to the bug tracker, that is the easiest way for devs to figure out whether it is bug or not. Ton and Brecht are the constraints and armature experts.

LetterRip

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