Constant interpolation ignored, even with all keyframes using it

[Orso2p2n]

Describe the bug
When exporting a scene with actions that use only constant keyframes, the exported gltf still uses LINEAR interpolation.

To Reproduce
Steps to reproduce the behavior:

1. Download the example file.
2. Observe that all the keyframes of the "idle" action use constant interpolation
3. Export in GLTF with Animation mode on "Actions".
4. Open model in gltf viewer.
5. Observe that the animation still uses linear interpolation.

(Alternatively, export the model using glTF Separate, and open the .gltf in a text editor to see that it still uses "interpolation: LINEAR" for most of the samplers)

Expected behavior
According to #2137, having all the keyframes use constant interpolation should export using STEP.

Screenshots
The animation in Blender:

The animation in gltf viewer:

.blend file/ .gltf (mandatory)
character.zip

Version

• OS: Windows 10
• Blender Version: 4.1.1

[julienduroure]

Hello,

Most (didn't check every individual channels, but some of them) channels that become "LINEAR" are some bone channels that are not animated in your model.

CONSTANT are kept as STEP, but for not directly animated bones (like any deformation bones) are currently exported as LINEAR, as we don't have any interpolation information.

An enhancement that can be done is to let the user choose what interpolation should be used when sampling not animated bones

[Orso2p2n]

Thank you for your answer!

Is there a way for me to work around this problem, without having to replace all the instance of "LINEAR" by "STEP" in the gltf file every time i export?

I tried adding a keyframe with constant interpolation for every channel, and setting those channels' extrapolation mode to Constant Extrapolation, to no avail.