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# Objective *Fixes #5670 as an opt-in for now* glTF uses the following coordinate system: - forward: Z - up: Y - right: -X and Bevy uses: - forward: -Z - up: Y - right: X For the longest time, Bevy has simply ignored this distinction. That caused issues when working across programs, as most software respects the glTF coordinate system when importing and exporting glTFs. Your scene might have looked correct in Blender, Maya, TrenchBroom, etc. but everything would be flipped when importing it into Bevy! ## Solution Add an option to the glTF loader to perform coordinate conversion. Note that this makes a distinction in the camera nodes, as glTF uses a different coordinate system for them. ## Follow Ups - Add global glTF loader settings, similar to the image loader, so that users can make third-party crates also load their glTFs with corrected coordinates - Decide on a migration strategy to make this the future default - Create an issue - Get feedback from Patrick Walton and Cart (not pinging them here to not spam them) - Include this pic for reference of how Blender assumes -Y as forward:  ## Testing I ran all glTF animation examples with the new setting enabled to validate that they look the same, just flipped. Also got a nice test scene from Chris that includes a camera inside the glTF. Thanks @ChristopherBiscardi! Blender (-Y forward):  Bevy (-Z forward, but the model looks the wrong way):  Bevy with `convert_coordinates` enabled (-Z forward):  Validation that the axes are correct with F3D's glTF viewer (+Z forward): 
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| title | authors | pull_requests | ||
|---|---|---|---|---|
| Allow importing glTFs with a corrected coordinate system |
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glTF uses the following coordinate system:
- forward: Z
- up: Y
- right: -X
and Bevy uses:
- forward: -Z
- up: Y
- right: X
This means that to correctly import glTFs into Bevy, vertex data should be rotated by 180 degrees around the Y axis.
For the longest time, Bevy has simply ignored this distinction. That caused issues when working across programs, as most software respects the
glTF coordinate system when importing and exporting glTFs. Your scene might have looked correct in Blender, Maya, TrenchBroom, etc. but everything would be flipped when importing it into Bevy!
Long-term, we'd like to fix our glTF imports to use the correct coordinate system by default. But changing the import behavior would mean that all imported glTFs of all users would suddenly look different, breaking their scenes! Not to mention that any bugs in the conversion code would be incredibly frustating for users.
This is why we are now gradually rolling out support for corrected glTF imports. Starting now you can opt into the new behavior by setting the GltfLoaderSettings:
// old behavior, ignores glTF's coordinate system
let handle = asset_server.load("fox.gltf#Scene0");
// new behavior, converts glTF's coordinate system into Bevy's coordinate system
let handle = asset_server.load_with_settings(
"fox.gltf#Scene0",
|settings: &mut GltfLoaderSettings| {
settings.convert_coordinates = true;
},
);
Afterwards, your scene will be oriented such that your modeling software's forward direction correctly corresponds to Bevy's forward direction.
For example, Blender assumes -Y to be forward, so exporting the following model to glTF and loading it in Bevy with the new settings will ensure everything is oriented the right way across all programs in your pipeline:
If you opt into this, please let us know how it's working out! Is your scene looking like you expected? Are the animations playing correctly? Is the camera at the right place? Are the lights shining from the right spots?