GLTF Export Bug: FreeCamera rotation has wrong offset

Bugs
1

Hi team,

There is a rotation offset bug with freecamera GLTF exports.

The exported freecamera wrongly adds a rotation offset that is equal to its parent.
Suppose freecamera.parent = tnode;
If tnode.rotation.z = 90 degrees, the exported GLTF will ALSO have freecamera.rotation.z = 90 degrees. This results in the camera having a total rotation.z of 180 degrees, which is weird

Here is a simple PG: https://playground.babylonjs.com/#HZBCXR#99

Before export
90 degrees
image

After Export
180 degrees
(Loaded this in sandbox BJS)
image

You can see that the Z rotation offset accumulates based on its parent Z rotation.

2

cc @Guillaume_Pelletier and @bghgary

3

Hello,
this is perfectly legit into GLTF camera documentation, where the camera might be attached to a node to define the orientation.
But from Babylon Point of view, a camera is NOT a transform node

When exporting, scene is defined as a node list using the following statement.

const nodes: Node[] = [...babylonScene.transformNodes, ...babylonScene.meshes, ...babylonScene.lights, ...babylonScene.cameras];

and camera objects are binded later to the corresponding node.

if (babylonNode instanceof Camera) {
    glTFNode.camera = cameraMap.get(babylonNode);
}

consequently, into GLTF, the camera inherit from his parent transformations.

4

Yes, the thing is it’s not just BJS, Blender also imports the GLTF with the wrong rotation offsets in the exact same way
So I think solving this issue (perhaps like you suggested KEEP_BABYLON_CAMERA_BEHAVIOUR in the export code) would be extremely useful for lots of people who use cameras in BJS

5

I don’t think this is right. If you change the transform of the parent of the camera, it moves the camera.

6

Is there going to be a PR for this :face_with_head_bandage:

7

@Guillaume_Pelletier Can you take another look?

9

ya right… :upside_down_face:

10

I’m going to dig in this week, seems my first assumption were wrong and some stuff may be corrected with the camera export.

11

any updates on this PR? :slight_smile:

12

@Guillaume_Pelletier

13

@Guillaume_Pelletier is aware of this. He will be back on this soon. :slight_smile:

14

Published a PR on the subject.

15

Can’t wait to test this out!

16

Is this also fixed for lights too? I believe it also has a similar issue, if I’m not mistaken

17

Only focus on the camera for this PR.