Influenced animations

[bartiss]

Hi,

Imagine a VERY big, six-legged mosnter walking around a hilly terrain. All of his walk animations are prepared to work well on a flat surface, so it's easy to imagine how bad does it look like now. His legs dissappear in higher hills and float in the air above lower terrain.

Let's suppose I know where and how to orient each leg so it stays on hill's surface. I know I can set each bone to be manually controlled, but then the animation stops working. So it's either manual control or animation.

Is there any way to blend it somehow? Just like Euphoria does (http://www.youtube.com/watch?v=Qi5adyccoKI)

[buckED]

What you need is called inverse kinematics.
I'm not sure whether or not it has been realised for ogre yet though.
Just try searching the forums and the Wiki.
If I am not mistaken one of the summer of code projects was an attempt
at IK with ogre.

[lebensborn]

Not what you're looking for but maybe you could use the surface normal to align the mesh with the surface of the terrain at least? World of Warcraft does this.

[bartiss]

What you need is called inverse kinematics.

IK is the way to calculate linked bone orientations. If I pull a hand the forearm and arm will "respond" correctly.
So I got rotations of all bones calculated, but how can I blend those with the ones coming from animation currently running?

Not what you're looking for but maybe you could use the surface normal to align the mesh with the surface of the terrain at least? World of Warcraft does this.

The alignment is done, but it doesn't help. The monster is too big. I'm starting to consider manual animation of legs only and leaving the rest of the body to be animated the usual way.

[lebensborn]

This isn't the best way but might work, although wouldn't be very accurate...

Make an offset vector for each leg, parent it and position it to the end of each foot bone.

Make an update function which checks the distance of the offset vector to the terrain below it, then add the distance value to the bone rotations somehow, you will probably need to play about with the value untill it looks more or less correct.

If you used a multiplier on the distance value, you could use the steepness of the terrain to vary the multiplier, which in turn would vary the bone rotations. So on steep terrain it would add more rotation to the bones, and on none steep areas it would add less rotation. With a little tweaking it might look ok.

[xavier]

What you need is IK plus collision -- in other words, what you need is to use Havok for animation. Collision will align the feet to the land, and IK will put the rest of the bones where they need to go. The Havok demos have an example of this.

[bartiss]

All your answers are correct but that's not what I meant guys!

I just wanted to know how to do it in Ogre. Not how to calculate bone rotations, collisions, etc.
Let's assume I have to sets of data:
A - all bones rotations taken from AnimationSet
B - some bones rotations calculated on the fly (feet collision with terrain for example, but could be anything else)

And now, how do I apply set B?
First thing I thought of was setting appropriate bones to manual control, but that leaves me with B set only. Premade animations don't work with manually controlled bones. I would like to apply set A to get the default movement animation and then correct it with set B, so the feet don't sink into terrain (for example).

So the question is if it's possible at all to change bone rotations set by AnimationState on the fly.

[bartiss]

Sorry for bumping. I really need to know if I should give up on this one.

I'm not exactly sure how Ogre manages animation states, but I think something like this might work:

1. let Ogre do the bone transformations using current animation state
2. take control of the bones and align them the way you like
3. render
4. turn off manual control of bones

Is it possible without manipulating within Ogre source?

[lebensborn]

Just looked in the wiki for you, this might help. http://www.ogre3d.org/wiki/index.php/Ma ... llingBones

[Praetor]

Or better: AnimationTrack::Listener

Create a second "ghost" animation track for your object (keep the original). When the listener is called, get the interpolated keyframe from the original track which will be where the animation should be. Now, influence that any way you want (IK info, physics engine, etc.) and then return that tweaked keyframe. Make sure you play your ghost animation and not the original.

[bartiss]

Thanks Praetor, that's something completely new to me. I've looked into API docs and I think that's exactly what I need.
I don't think I can find any tutorials or demos implementing this (or using AnimationTrack at all), so I'll post some more quiestions here.

I know I can get Animation object from a skeleton. Then I get AnimationTrack from Animation. And even a KeyFrame.
But how do I modify bone rotations now? I can't see any way to access them through Animation, AnimationTrack or KeyFrame.
And how do I know if AnimationTrack::Listener is being called?
And finally, how do I make sure that I play "my" animation and not the original one?

[madmarx]

From Animation -> the different animation track. What you want is nodeAnimationTrack (since bone is a special node).
Then from (Node)AnimationTrack -> the bone (through getAssociatedNode).
Then setup your listener.

Then I suppose you just need to do something like :
virtual bool getInterpolatedKeyFrame (const AnimationTrack *t, const TimeIndex &timeIndex, KeyFrame *kf)
{
1/ first dynamic cast t to see if its a nodeAnimationTrack (or you can just check the name of the parent animation)
2/ get the associated node.
3/ get the name of the associated node. (so you know which bone it may be).
4/ you just need to modify the values of kf (kf is already constructed, but not with good values).
5/ if you don't want to touch this animation, just return false.
}

cf line 378 of ogreanimationtrack.cpp in the svn.

[bartiss]

Thnak you very much madmarx!
I will try it first thing in the morning

[azzolini]

Ok, but it would be better to have an example about how to setup the listener.

Ogre::AnimationState *anim = scene->GetAnimationState("ruota");
unsigned short howmany = mSceneMgr->getAnimation("ruota")->getNumNodeTracks();

Ogre::NodeAnimationTrack *traccia = mSceneMgr->getAnimation("ruota")->getNodeTrack(1);

now i get a pointer to the tracknode but i cannot figure how to set up the listener!

in OgreAnimationtrack.h you have...

Code: Select all

class _OgreExport Listener
		{
		public:
			virtual ~Listener() {}

			/** Get an interpolated keyframe for this track at the given time.
			@returns true if the KeyFrame was populated, false if not.
			*/
			virtual bool getInterpolatedKeyFrame(const AnimationTrack* t, const TimeIndex& timeIndex, KeyFrame* kf) = 0;
		};

and..

Code: Select all

		/** Set a listener for this track. */
		virtual void setListener(Listener* l) { mListener = l; }

so, i suppose it would be something to do with traccia->setListener(??);

Please can anyone help me?
Thank
Lorenzo