[Solved] Variable versus Constructor with addRotation

[JohnK]

Having had a look at the playgrounds using Jerome's new addRotation I started wondering about line 39 in http://www.babylonjs-playground.com/#1PON40#4

torus.rotation.copyFromFloats(0.0, 0.0, Math.PI / 2);

the torus had already been set as vertical so why was it necessary to re-do it. On commenting out this line and running the PG again the wheel wobbles (quite a lot very soon). So I decided it had to do with stopping error accumulation. My next thought was why copyFromFloats and not just use.

torus.rotation = new BABYLON.Vector3(0, 0, Math.PI/2);

This does work as in http://www.babylonjs-playground.com/#1PON40#9

From advice about something else that Jerome gave me I decided that it had something to do with avoiding constructing new variables and garbage collection. My next thought was would this be avoided if I set a variable to be the vector3 (0, 0, Math.PI/2) and used this each time.

So I created

var vRot = new BABYLON.Vector3(0, 0, Math.PI/2);

and then in the render loop used

torus.rotation = vRot;

result more extreme wobbling as in http://www.babylonjs-playground.com/#1PON40#10. If you do a console.log(vRot) in the loop its value changes.

The simple question is why? What fundamental misunderstanding have I made this time? (Probably something to do with my use of Javascript rather than BJS)

[adam]

Javascript is "pass by reference" when setting objects.

[JohnK]

Of course any changes in torus.rotation are also made to vRot. Thank you @adam knew it was something simple I should already know.

[jerome]

Well, the goal of addRotation() is to compute the final value of mesh.rotation step by step.

I don't know this final value (and I don't care), I just want my mesh rotated this way, then this way, etc.

So, I need to begin each frame from a starting state rotation.z = PI /2, then to add my steps to reach the final wanted orientation.

I can't keep the last stored values, because the next use of addRotation() will accumulate a new rotation on this last state what will lead to something unpredictable (by me).

Just keep in mind that the WorldMatrix needs only a final value in the property rotation (or rotationQuaternion) whatever the way this value is set : manually or by using addRotation() or rotate()

I've added a summary in the rotation doc here : https://github.com/BabylonJS/Documentation/blob/master/content/overviews/Standard/How_Rotations_and_Translations_Work.md