Bones questions [3DS Max]

Oogst · Post by **Oogst** » Tue Mar 28, 2006 11:39 am

I am getting some errors with the bones an artist in my team made, which makes me wonder about how bones work exactly. These are the things I wonder about:

1. Is it allowed to animate the scale or position of a bone?

2. How can it be that multiplying the normals with a world matrix gives correct normals? If the matrix does translation, won't that translate the normal as well, giving totally false directions, even after normalizing?

3. Is it allowed to create bones that are already scaled before skinning? So I create bones, scale them randomly, and then I apply them to a mesh and animate them? Unfortunately, one of the animators in my team did this and I get the errors below, but I wonder whether this is really the course, or he made some other errors as well that cause this stuff.

4. Does it matter if bones have negative scale? So (-1, -1, -1) instead of (1, 1, 1). On of the legs in the picture below has this, but is okay, while one of the arms has this as well and is totally broken.

BTW: The weird bone is to animate his belly, not something else.

Post by **sinbad** » Tue Mar 28, 2006 6:14 pm

1. Yes

2. Only the rotational element of the transform is used on the normals.

3. Yes, I suspect your problems are specific to the 3DS exporter, which we can't currently support in the core team due to the lack of licenses.

Oogst · Post by **Oogst** » Tue Mar 28, 2006 6:31 pm

Thanks for the clear answers!

If I wanted to take a look at the 3dsmax-exporter, have you got any suggestion as to where the problem might be? Do you think it is in the way the bones are exported, or the animations, or something else? Also, if I would find something and create a patch, would anyone look at it and fix it? I submitted another patch a week ago, and so far it was not assigned to anyone. Will it be ignored, or will patches be checked after some time?

Ow, by the way: it is a pity if 3dsmax is not 'officially' supported, for it is by far the most popular modelling-tool among game professionals. I do understand the license problem, though, of course.

Post by **xavier** » Tue Mar 28, 2006 8:27 pm

It means that Autodesk will not come off a license or two to allow the team to develop an exporter for Ogre, which in turn means that Max export for Ogre relies on community efforts.

I strongly suggest not using the MaxScript exporter, and instead using oFusion (ofusion.inocentric.com). Alternately, you can look at helping test the plugin-based exporter I am working on. The source is in CVS in the same place as the maxscript stuff.

Oogst · Post by **Oogst** » Thu Mar 30, 2006 9:38 am

Ah, well, but I have my own tools that are built on top of the MAXscript-exporter, so switching to oFusion will not be simple and will take a lot of work, which I surely cannot put into it during the project I am working on right now.

Anyway, I think I have an example of that Sinbad's answer might be incorrect. I asked whether bones can be scaled statically prior to skinning and animating and Sinbad said that this can be done and if there is a problem, it is in the MAXscript exporter. I think I made an example that shows that this is not true, but I am not sure.

In the picture below, I linked the sphere to the green dummy and then created a rotation-animation for the dummy. The dummy is linked to the brown box at the center. Now when I scale the box, the movement of the sphere becomes an ellipse. The movement is visualised by 3dsmax in red. Does this not imply that scaling breaks the rotation-animation and is indeed a serious problem with bones?

Oogst · Post by **Oogst** » Sun Apr 02, 2006 2:14 pm

Still, can someone tell me whether it would be possible for the bones in Ogre to represent the above rotation? If it would be possible, scaling bones before animating would be possible, but otherwise it would not be possible.