GLTF Export Bug: FreeCamera rotation has wrong offset

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:

Before export
90 degrees

After Export
180 degrees
(Loaded this in sandbox BJS)

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

cc @Guillaume_Pelletier and @bghgary

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) { = cameraMap.get(babylonNode);

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

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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

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

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

@Guillaume_Pelletier Can you take another look?

ya right… :upside_down_face:

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

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any updates on this PR? :slight_smile:


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


Published a PR on the subject.


Can’t wait to test this out!

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

Only focus on the camera for this PR.