Rotate Mesh but keep child axis orientation

[valepu]

I've tried searching google on this but i can't seem to find a solution.
What i want to achieve is that if i set a rotated mesh as parent then translating it through an axis would move it in the same direction as if it didn't have a rotated parent. For example in this playground 

http://www.babylonjs-playground.com/#26DEBS#0

I would like the sphere to go "up" rather than towards the camera.

 

[adam]

I would add an empty mesh in between the ground and the sphere and rotate it to negate the rotation of the ground.

http://www.babylonjs-playground.com/#26DEBS#2

[dbawel]

I don't understand your question. Could you explain actual usage?

Cheers,

DB

[valepu]

8 minutes ago, dbawel said:

I don't understand your question. Could you explain actual usage?

Cheers,

DB

I create a mesh A, rotate it by 90° on the X axis

I create a mesh B and set A.parent = B

i translate B on the y axis, but it doesn't move on the global y axis ("up"), it moves on the parent's rotated axis

 

The additional mesh could work but i was wondering if there's a more "conventional" solution (like a special rotation function that uses world axis)

[JohnK]

The idea of a parent is that the child moves relative to the parent.

This page from the documentation describes some of the relationship between parent and child and positions and rotation.

http://doc.babylonjs.com/tutorials/Position,_Rotation,_Scaling

This page from the documentation does not deal with parenting but does show rotation and translation  using the world axis

http://doc.babylonjs.com/tutorials/Position,_Rotate,_Translate_and_Spaces

If you are simply doing a rotation of -PI/2 as in your PG then you know that the z axis of the ground in now screen up as in http://www.babylonjs-playground.com/#26DEBS#8

If you want something more complicated then please try to describe the situation you are aiming for, it might all come down to when you set the parent.

[valepu]

I know the theory behind and i know i could just translate it over the right axis. My problem lies on the fact that i might have a function that should be "mesh agnostic" and does a translation over an axis. Say:

function goUp(mesh) {
    mesh.position.y += 1;
}

 

if i pass to this function a mesh with a rotated parent (any kind of rotation) it won't move the mesh "up"

Mind that this is just an example (and i don't have a more concrete one) so using another approach is not the solution here

[adam]

What's wrong with my answer?

[valepu]

2 minutes ago, adam said:

What's wrong with my answer?

Nothing, i'd just like to know if there's (or if it can be implemented) a "native" method to do that

[adam]

Another possible solution is rotating the vertices of the parent instead of rotating the coordinate system.

Edit: performance is much worse with this solution though.  If you are going to be rotating the parent every frame, I would go with the extra mesh solution. 

[adam]

http://www.babylonjs-playground.com/#26DEBS#9

[valepu]

Thanks, i guess that's the closest one can get to a "native" function

[adam]

Looks like there actually might be a more conventional solution.  Look at changing the frame of reference at the bottom of this page.

https://doc.babylonjs.com/overviews/How_Rotations_and_Translations_Work

Edit:  I didn't have any luck getting a playground working using TransformCoordinates.  Maybe someone else will.

 

 

[dbawel]

There are many good solutions that would work, however now that I understand what you want to do, simply parent both mesh A and B to a null or transperent object. Then rotate mesh A and translate mesh B all you want. And if both must translate together, then translate the parent object.