get a bone for location of weapon fire

[Nickak2003]

Do I use bone->_getDerivedPosition for the spot where a bullet should fire from? Ive tried it and it is not correct from the bone placement in blender. It must be either a blender problem, an exporter problem, or I'm not using ogre correctly?
here is what I'm doing to try to get the position to fire from:

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		Ogre::Entity* spaceShip1 = Graphics::get().getSceneManager()->createEntity("jet1.mesh");
		Ogre::SceneNode* sn = Graphics::get().getSceneManager()->getRootSceneNode()->createChildSceneNode();
		sn->attachObject(spaceShip1);

		Ogre::Skeleton* skel = spaceShip1->getSkeleton();
		Ogre::Bone* bone = skel->getBone("leftgun");

             
		locationOfGun = bone->_getDerivedPosition();

Is this correct?

[dark_sylinc]

IIRC that transform is local to the object.

If my math doesn't fail me, you need to do:

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locationOfGun = sn->_getDerivedPosition() + sn->_getDerivedOrientation() * (sn->_getDerivedScale() * bone->_getDerivedPosition());

Take in mind that Ogre bones are at the head of the bone, while Blender bones have a head and a tail. If you need the position of the tail, then create another connected bone, so that the head of this new bone will be where the tail of the previous bone is.

[c6burns]

If the bone is part of a larger skeletal heirarchy, you need to traverse upwards ... because yes as dark_sylinc is explaining the bone position is in local space

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Ogre::Vector3 GetBoneWorldPosition(Ogre::Entity* ent, const Ogre::String &boneName)
{
	Ogre::Bone* bone = ent->getSkeleton()->getBone(boneName);
	Ogre::Vector3 world_position = bone->_getDerivedPosition();
 
	//multiply with the parent derived transformation
	Ogre::Node *pParentNode = ent->getParentNode();
	Ogre::SceneNode *pSceneNode = ent->getParentSceneNode();
	while (pParentNode != NULL)
	{
		//process the current i_Node
		if (pParentNode != pSceneNode)
		{
			//this is a tag point (a connection point between 2 entities). which means it has a parent i_Node to be processed
			world_position = pParentNode->_getFullTransform() * world_position;
			pParentNode = pParentNode->getParent();
		}
		else
		{
			//this is the scene i_Node meaning this is the last i_Node to process
			world_position = pParentNode->_getFullTransform() * world_position;
			break;
		}
	}
	return world_position;
}

[Kojack]

Here's the shortcut.

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locationOfGun = sn->convertLocalToWorldPosition(bone->_getDerivedPosition());

It does all the hierarchy transform stuff internally.

There's also sn->convertLocalToWorldOrientation for orientation (so you can make the bullet move in the direction of the bone, in case it's a turret), and world to local versions of both functions.

[c6burns]

So much easier than mine! Thanks, Kojack!

[Nickak2003]

Thanks! So in blender, the bone head is not aligning with the cursor head, what is the problem? here is a pic:

[Nickak2003]

Nevermind, figured it out, the armature had an offset

[sdong21]

This solution works for almost all conditions, thanks!
The other function convertLocalToWorldPosition(mBone->_getDerivedPosition()) only works when it has no large skeletal heirachy according to my test.

If the bone is part of a larger skeletal heirarchy, you need to traverse upwards ... because yes as dark_sylinc is explaining the bone position is in local space

Code: Select all

Ogre::Vector3 GetBoneWorldPosition(Ogre::Entity* ent, const Ogre::String &boneName)
{
	Ogre::Bone* bone = ent->getSkeleton()->getBone(boneName);
	Ogre::Vector3 world_position = bone->_getDerivedPosition();
 
	//multiply with the parent derived transformation
	Ogre::Node *pParentNode = ent->getParentNode();
	Ogre::SceneNode *pSceneNode = ent->getParentSceneNode();
	while (pParentNode != NULL)
	{
		//process the current i_Node
		if (pParentNode != pSceneNode)
		{
			//this is a tag point (a connection point between 2 entities). which means it has a parent i_Node to be processed
			world_position = pParentNode->_getFullTransform() * world_position;
			pParentNode = pParentNode->getParent();
		}
		else
		{
			//this is the scene i_Node meaning this is the last i_Node to process
			world_position = pParentNode->_getFullTransform() * world_position;
			break;
		}
	}
	return world_position;
}