Rotating a Mesh around a Pivot

[ChrisR]

But moving the pivot moves the mesh. So it still rotating in local space relative to the same pivot location. So if i move the pivot, the mesh moves the same amount. This has been my problem the whole time

[GameMonetize]

yes but the pivot happens before the rotation which means that you can set a translation in the pivot, do your rotation and then reset your position

 

No way to achieve this without the pivot. As you may know matrices multiplication are not associative: AxB != BxA

 

the complete matrices chain in bjs is: PivotMatrix x Scaling x Rotation x Translation

[JohnK]

Recently I needed to rotate a mesh around a pivot and started out using a parent. In the project the camera was always fixed on the mesh and the pivot needed to move from frame to frame and I had problems keeping the mesh in its correct position. A search for "rotating" and "pivot" brought me back to this topic which I had forgotten. So I decided if I found a solution I would post it here.

@ChrisR sorry to have taken so long (over a year) and hope what follows is a solution to what you wanted, even if you have solved it another way I hope others might find it useful.

What I wanted was for a mesh to rotate around an line that did not pass through its local origin. Two things are needed to fix a line, a point that the line passes through and a vector representing the direction of the line. You can think of these as a pivot point and an axis.

Given a pivot point (pivotAt) and an axis (axis) and an angle (theta) for the rotation the following will rotate a mesh around the line.

var m = BABYLON.Matrix.Identity().setTranslation(mesh.position.subtract(pivotAt));
var invm = m.clone().invert();
var r = BABYLON.Matrix.RotationAxis(axis,theta);
var ar = m.multiply(r).multiply(invm);
mesh.setPivotMatrix(ar);

http://www.babylonjs-playground.com/#29BGXO#3

[DigiHz Data]

@ChrisR

Have you found a solution for this problem yet?

I understand exactly what you mean, and i am trying to achieve the same thing.

See topic http://www.html5gamedevs.com/topic/26132-getpivotmatrix-xyz-local-values/?page=1

 

[DigiHz Data]

A solution might be ths PG.

http://www.babylonjs-playground.com/#M0UJB