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Skeletal animation query.

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I've been reading up on skeletal animation and many documents often seem to transform their bone matrices with respect to the "bind pose" of the skeleton. I'm wondering why it's necessary to use the bind pose. Currently, how we do this in our project is to use the first frame of the animation (not the bind pose) as the reference and transform the bones with respect to this in every subsequent frame. Can anyone tell me why some folks prefer the bind pose?

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it's actually quite simple to explain why a "bind pose" is necessary:

Normally, the bind pose is the pose that the character has, when it is in it's initial pose. Mostly, you're using the arms spread to left and right and the legs straight done (also know as "jesus pose" (tm) ). In this pose, the character is absolutely neutral. This means, that no controller or any other bone manipulator is applied to the character.

Now, when you're animating the character, the base "bind pose" for all animations is the same. You don't have another bind pose for the "running animation" than for the "walk animation" or the "hit the other char with my bloody sword animation". Therefore you only have to calculate once the "bind pose" when loading the character (you even can store the bind pose in the character file if you want to).

When using your system (using the first frame of the animation), you have to recalculate the bind pose every time you load the animation to apply it to a character. This is unnecessary work.

Also, your system would mean that you have to have the exactly the same base start frame for all your animations since if you do not, you will not be able to blend any two animations into one.

I also think that you might encounter some problems when you scale or even actually pre-transform you character into the world. If you don't have those problems, you might be using a bind pose even without knowing it (by i.e. taking into account the base skeletal pose every frame).


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