Bones manipulation (Page 1 of 2)

To be correct you need to use the matrices, after the armature parenting is computed,
you multiply the entity matrix with the bone matrix :

MMatrix4x4 boneWorldMatrix = (*entity->getMatrix()) * (*bone->getMatrix());

All meshs are instances, so because multiples entities can use the same mesh
you need to update the armature for each entity (depending on the entity current animation) before retrieving the bone matrix :

MMesh * mesh = entity->getMesh();
if(mesh)
{
    MArmature * armature = mesh->getArmature();
    MArmatureAnim * armatureAnim = mesh->getArmatureAnim();
    if(armature)
    {
        // animate armature
        if(mesh->getArmature())
        {
            MArmature * armature = mesh->getArmature();
            if(mesh->getArmatureAnim())
            {
                animateArmature(
                    mesh->getArmature(),
                    mesh->getArmatureAnim(),
                    entity->getCurrentFrame()
                );
            }
            else
            {
                armature->processBonesLinking();
            }
        }
    }
}

this computation is otherwise only done at rendering if the entity is visible.

How do I now set the bone position to say world position P(0,0,0)?

Last edited by 255 (2013-08-18 22:36:40)

About math and matrices :
- http://www.gamedev.net/page/resources/_ … ices-r3097
- http://www.gamedev.net/page/resources/_ … ified-r695

So I was trying to do the same with rotation, and of course I'm failing.
Basically I have to copy the rotation of an object to the rotation of the bone to create a ragdoll.

Last edited by 255 (2013-10-06 10:07:35)

With this code, while the object rotates in the Y axis, the bone rotates in the Z axis.

I already tried to set bones rotation to zero in Blender, but it was all the mesh that was rotated towards the wrong axis eheh. Now it works.

are the two bones in the same armature ? or not necessary ?

Probably something like that :

// targetBone is the bone to copy the transformation from
// bone is the bone to copy the transformation to
// the two bones need to be in the same armature

MMatrix targetMatrix = (*targetBone->getMatrix()); // get target bone matrix (in armature space)

// if "bone" is linked to another bone
MObject3d * parentBone = bone->getParent();
if(parentBone)
{
    // calculate target matrix in parentBone's space
    targetMatrix = parentBone->getMatrix()->getInverse() * targetMatrix;
}

// get position and rotation coords from targetMatrix
bone->setPosition(targetMatrix.getTranslationPart());
bone->setEulerRotation(targetMatrix.getEulerAngles());

What is important is to know what space you are, world space, armature space or parent space.

Yes, it works, and if the bones really overlap you can also simply do

bone->setRotation(targetBone->getRotation());

and that's enough. In other cases your code works better.
So, yeah, the problem lies somewhere else in my code.
Debugging time! lol
Thanks for the help.

I'm back working on my ragdoll system and I have problems.

I have a ragdoll made of ragdoll parts.
Each ragdoll part is just a parallelepiped entity which visually simulates the bone.
Each ragdoll part is in world space (they are parented only with constraints).
I have a characterEntity and its armature.
The armature should "follow" the ragdoll (and this is what is not quite working).

First, at the start of the game, I position and rotate each ragdoll part, copying the position and rotation from the bones.
Then, I let the physics run and each step I do the inverse: I rotate every bone to match the ragdoll part rotation, so the mesh should animate and fall down to the floor.

It works almost fine but there is some kind of offset, e.g. the leg's bone is ~15° off on the X axis in respect to the ragdoll part, the arm's bone ~ the same, etc.
The ragdoll is currently only about the skeleton, so it's not about e.g. the arm not being perfectly in line with the bone or uncorrectly colliding: I'm making a ragdoll of the skeleton only. Only when this works, I will attach actual body parts for the collisions.

My code is actually pretty long, complex, and separated into classes and files, I just can't post it all. But I'm pretty sure the problem is only about matrices and rotation, and lies here:

[...]
        //Ragdoll's part copys rotation from bone (works perfectly fine)
        MMatrix4x4 boneWorldMatrix = (*characterEntity->getMatrix()) * (*bone->getMatrix());
        ragdollPart->setEulerRotation(boneWorldMatrix.getEulerAngles());
[...]
        //Bone copys from Ragdoll's part (DOESN'T WORK)
        MMatrix4x4 myMatrix = characterEntity->getMatrix()->getInverse() * (*ragdollPart->getMatrix());
        MObject3d* parentBone = bone->getParent();
        if(parentBone)
            myMatrix = parentBone->getMatrix()->getInverse() * myMatrix;
        bone->setEulerRotation(myMatrix.getEulerAngles());
[...]

The grey lines are the ragdoll parts. They are in "x-ray mode".
The red little squares are the bones (the head of every bone).
In the image on the left, the game is just started, and everything is right. The ragdoll parts are positioned and rotated copying the bones position and rotation from the armature.
As soon as I activate the physics (only one step of physics), you can see how the bones don't match the ragdoll parts correctly.

Last edited by 255 (2014-02-09 17:00:25)

Well it's actually complex for me too, I've still not grasped matrices and stuff quite well I guess eheh.

There's no need. Since I never change the position (only at the start) and I change only the orientation of the bones, you can be sure that the orientation is simply what goes from a red dot to the other. The position changes automatically thanks to parent-child relationships between the bones, as a "side-effect" of the rotation changes.

Last edited by 255 (2014-02-09 17:52:51)

My for loop is

for(i=0; i<bonesNumber; i++)

and the mesh has one single root bone, which is bone 0.
After each bone is rotated, I do:

armature->processBonesLinking();
armature->updateBonesSkinMatrix();

inside the brackets of the for loop, and then I process the next bone (i++).
So I don't really think that the problem is about order.

I will try your code anyway and let you know.

Last edited by 255 (2014-02-09 20:32:07)