I'm completely confused (https://github.com/urho3d/Urho3D/issues/1961)

I’m really sorry if I said something which could be interpreted as offensive,
I really did not intend to and I don’t understand what happened.

@Lumak, @weitjong

This is about the following issue:

As the result of other topic and thanks to comments from people I understand the logic behind
rotation (probably not logic, but merely a system, but that is not important detail).
But I still don’t understand about LookAt. It is misbehaving in my point of view.
I tried to get some insight, but for some reason people were offended. I really don’t understand why,
I’m just looking for truth. I really respect you all. Please don’t be like that.

The problem is caused by the axis that You use as forward - take a look at image lower: I have attached same “look at teapot” script to both mutant and ninja:

  • positive Z is used as forward for ninja and script works fine, ninja is looking at teapot;
  • in case of the mutant forward is negative Z and mutant is looking in opposite direction

Long story short - to use LookAt, forward should be positive Z otherwise You’ll have to invert results

Thanks for your answer!

However, I export via Blender exporter in Front mode (-Y+Z) which means Z-front.
And if I move in Z+ direction the model moves and rotates properly, I don’t need to fixup.

Can actual bone rotations affect this?

So do I have to have Z-forward on actual bone, this is question which is last one on this particular thing.

In blender, select all bones then press ctr+n (or space and search for Recalculate Roll) and pick “Global +Y Axis”

Will this change affect existing animations?

Oh, I haven’t thought about that. Unfortunately yes.

So basically LookAt will not work if bone is not Z-front, right?

In angel script:

            head.LookAt(lookAt.position);
            Quaternion rot = Quaternion();
            rot.FromLookRotation(-head.direction, Vector3::UP);
            head.rotation = rot;

head is head bone, lookAt is target to look at.

EDIT:
one more thing ; since LookAt function is already calling FromLookRotation, it may be a better idea to actually modify or create new LookAt function that calls FromLookRotation with ‘-direction’ so it wouldn’t be called twice.

Is there some generic way possible, i.e. is it possible for me to get bone initial rotation and compensate?
Hardcoding such things is getting in huge trap in future…

This is how it currently works with correction. There is no way to make NPC look directly at camera
or directly at anything. Some correction i needed, but I don’t know how to calculate it.

Current looking code:

void BTBlackboard::HandleSceneDrawableUpdateFinished(Urho3D::StringHash eventType, Urho3D::VariantMap& eventData)
{
        Node *head = node_->GetChild("head", true);
        Node *spine = node_->GetChild("spine02", true);
        Node *root = node_->GetChild("root", true);
        AnimatedModel *anim = node_->GetComponent<AnimatedModel>(true);
        Skeleton skel = anim->GetSkeleton();
        Bone *head_bone = skel.GetBone("head");
        Bone *spine_bone = skel.GetBone("spine02");
        Quaternion head_r = head_bone->initialRotation_;
        Quaternion spine_r = spine_bone->initialRotation_;
        if (look_at_enabled && look_at) {
                Node *lookat_target = look_at;
                PODVector<Node *> children = look_at->GetChildrenWithTag("player");
                if (children.Size() > 0) {
                        lookat_target = children[0];
                        VariantMap vars = lookat_target->GetVars();
                        bool first_person = vars["first_person"].GetBool();
                        if (first_person)
                                lookat_target = (Node *) vars["camera_node"].GetPtr();
                        else {
                                URHO3D_LOGINFO("no camera");
                                lookat_target = look_at->GetChild("head", true);
                        }
                } else {
                        lookat_target = look_at->GetChild("head", true);
                }
                if (!lookat_target)
                        lookat_target = look_at;
                URHO3D_LOGINFO("looking at: " + lookat_target->GetName() + " " + lookat_target->GetWorldPosition().ToString());
                URHO3D_LOGINFO("from: " +  head->GetWorldPosition().ToString());
                Quaternion prep;
                Vector3 dir = (lookat_target->GetWorldPosition() - node_->GetWorldPosition() - Vector3(0.0f, 0.7f, 0.0f));
                URHO3D_LOGINFO("dir: " +  dir.ToString());
                prep.FromLookRotation(dir, Vector3(0.0f, 1.0f, 0.0f));
                Quaternion rot = root->GetWorldRotation();
                spine->SetWorldRotation(rot.Slerp(spine_r.Inverse() * prep, 0.5));
                head->SetWorldRotation(head_r.Inverse() * prep);
        }
}
1 Like

Rightfully so. But in this case the truth may lie in a lesson about stubbornness? :wink:
Glad this seems over with.

Nice progress, btw.

But still, the question persists - how to calculate correction in this case?