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Rotating a Bone in Cocos2dx Runtime

harikrishna

Hi All,

I have an archer who is shooting arrows at enemies, and since the enemies can be spread across the screen, i want to rotate the torso such that the arrow points at the person he is trying to shoot at,

I am unable to rotate it using the bone's fields, what i mean for example is:
spBone* torsoBone = skeletonNode->findBone("torso");
torsoBone->rotation += 100.0; // has no effect
torsoBone->appliedRotation += 100.0; // has no effect either
Note that i also tried calling skeletonNode->updateWorldTransform() before and after setting this and still no effect,
How would i go ahead and achieve the same?

Also note that i can get the effect i want by modifying the rotation inside the data of bone,
torsoBone->data->rotation += 100.0;
But i think this is not the right way to do it, cos after this, setToSetupPose to reset the rotation calls have no effect as the source data itself has changed.

Any ideas on the same?

Thanks in advance

Nate

Setting bone->rotation is one way to do it. You may want to apply animations, adjust the local rotation, then Skeleton updateWorldTransform. Are you applying an animation after changing the local rotation? That could overwrite your rotation change if the animation keys that bone's rotation.

Alternatively, you may want to apply animations, Skeleton updateWorldTransform so you can check Bone worldRotationX to see where the bone is pointing, then you could relatively adjust the local rotation to change the worldRotationX to the rotation you want, then Skeleton updateWorldTransform again. Note this won't work if your skeleton has nonuniform scale (different X and Y scale), because that squashes the local rotation into an oval and the world rotation won't be affected 1:1.

Another way to do it is to apply animations, then modify the world rotation using Bone rotateWorld. This works best if the bone you are rotating doesn't have any child bones. If it does, you'd need to call updateWorldTransform on each child bone. If those bones are affected by constraints, doing this may lose the changes the constraints made.

Another way to do it is to setup single bone IK in Spine, then position the IK target where you want the bone to point. This is likely the easiest solution. If the target's parent is the root bone and the root bone hasn't been moved from 0,0, then setting the local translation of the target to be where you want is easy (because the target's local and world translation are identical).

Isn't it nice to have options? 😉

harikrishna

Thank you for the patience in answering,

I actually tried what you had mentioned except for adding an IK, (dont want to do that as i dont want to add more tasks to the artist),
Let me give you more info on what is my use case, i play a arrow shoot animation, while it is being played, in the middle, i would want to change the rotation of the character, i have a bone which is the parent of the top body, which when i rotate rotates the top body,

If i do:
spBone* torsoBone = mSkeletonNode->findBone("torso2");
torsoBone->data->rotation += 10.0;

it works,

spBone* torsoBone = mSkeletonNode->findBone("torso2");
torsoBone->rotation += 10.0;

doesnt work

i would want the second approach cos then when i want to reset it, i can call setToSetupPose, when the animation is done.

May be my question should be why doesnt the second approach work? How would i get it to working?
(i tried updateWorldTransform calling before after etc and doesnt make any difference)

Edit:
By googling i found out that for the same in Unity you have to change in LastUpdate, only then it works, what about cocos2d-x, there is no LastUpdate

Mario

If you also apply an animation, you need to

Apply the animation
Set your rotation angles on your bones
Update the world transform of the skeleton

You may have to modify SkeletonNode for this.

Nate

Yep, please read my post carefully about the operations you need to perform.