Ragdolls: A how-to guide

[areay]

Hi guys,

Thought I'd post a wiki article on how-to do ragdolls. It's a first-cut but hopefully it's useful to someone http://www.ogre3d.org/tikiwiki/tiki-ind ... e=Ragdolls

P.S. If an Ogre forum admin reads this can I get it moved from the Sandbox into the physics section of the wiki how-to area? I don't seem to have to permissions to create there.

Cheers

[mkultra333]

Nice video of the troops being killed.

[lunkhound]

Nice article. I was recently working on something very similar (ragdoll type stuff with Ogre and Bullet). I ended up doing a couple of things differently on the Ogre side.

For bounding boxes, I had a bit of a problem because I had limbs that could detach and go flying. Ogre's static bounding boxes weren't working for me. I ended up modifying Ogre and got my change merged into Ogre 1.10. With my change, you can enable dynamic bounding boxes on a given entity like so:

Code: Select all

    mEntity->setUpdateBoundingBoxFromSkeleton( true );   // only in Ogre 1.10

This will make Ogre fit the bounding box around the entity's bones no matter where they go (but it will only consider bones that have influence over the mesh). There's also no need to update the scene node.

Also, instead of setting bones to be manually controlled (which kills all animation on those bones), I just set this on my Entity:

Code: Select all

    mEntity->setSkipAnimationStateUpdate( true );

Which means Ogre won't automatically apply animation to any of the bones. Instead I update the animation on the bones manually like this (each frame):

Code: Select all

    mEntity->getSkeleton()->setAnimationState( *mEntity->getAllAnimationStates() );   // push animation to skeleton bones

After doing that, I can read the orientation back from the bones and feed the result into Bullet constraint motors. Then run the physics update, and after that I read the transforms back from Bullet and plug them into the bones again. This can be used for powered ragdoll.
Being able to read back the animations and then selectively change them is also useful for IK or head tracking.

[c6burns]

Great article and great tips from lunkhound. Thanks! Kudos all around

[Lax]

Hi lunkhound,

Also, instead of setting bones to be manually controlled (which kills all animation on those bones), I just set this on my Entity:
CODE: SELECT ALL

mEntity->setSkipAnimationStateUpdate( true );
Which means Ogre won't automatically apply animation to any of the bones. Instead I update the animation on the bones manually like this (each frame):
CODE: SELECT ALL

mEntity->getSkeleton()->setAnimationState( *mEntity->getAllAnimationStates() ); // push animation to skeleton bones
After doing that, I can read the orientation back from the bones and feed the result into Bullet constraint motors. Then run the physics update, and after that I read the transforms back from Bullet and plug them into the bones again. This can be used for powered ragdoll.
Being able to read back the animations and then selectively change them is also useful for IK or head tracking.

You are my hero!! I nearly broke my head on this topic (weeks of painfull evaluation, try and error). I wanted a partial ragdoll (animation working but letting just the right arm to be a controlled via physics). But either animations did work but there was an ugly offset between the arm and the bones or animations did not work. I solved it like you described!

Best Regards
Lax