Prevent Frame interpolation

[yellowborb]

I would like to prevent Frame interpolation and force the animation of my glb to respect its initial framerate.

I can do that in the maya2gltf pluging and I would love to be able to do the same in blender, here is a picture of the arguments that allows me to do that in Maya (I think the -dsa is the most important)

An example of why this is important : If I animate an object disappearing from one frame to another by setting the scale from 1 to 0, then the interpolation will break the animation showing it scaling up or down. Thanks !

[julienduroure]

Hello,

I would like to prevent Frame interpolation

Any animation in CONSTANT interpolation in Blender should export using STEP in glTF. All component (for example scale.x scale.y scale.z) must have the same interpolation, to be sure to handle it correctly

Can you please upload an example test file where you struggle to export it correctly?

force the animation of my glb to respect its initial framerate

I maybe misunderstand what you mean, but you should be able to choose your sampling rate here:

Same here, in case of issue, can you provide a simple example.blend file?

[f3lix-s]

I had once "trouble" with frame interpolation, when I had a looping animation build with a "Cycles" fcurve modifier.

The result was something like this: after the torus scaled out of view, it scaled back to zero and over again ...

https://github.com/KhronosGroup/glTF-Blender-IO/assets/75536166/9314b927-5952-4d57-96cd-20647551b531

What i did, was baking the animation and then export the scene as .glb. Resulting problem was the interpolation on the way back to zero.

https://github.com/KhronosGroup/glTF-Blender-IO/assets/75536166/f7f70847-6f7d-433c-ab67-e8c30437190e

My solution was changing the fcurve interpolation to "constant" This resulted in a somewhat strange looking fcurve for a smooth movement,

but worked out for my needs.

Maybe the opportunity to bake animation modifiers, like "Apply Modifier" in Mesh, would be a helpful feature. "Bake All Object Animations" in export settings didn't do the job for me.

With this feature it would maybe make sense to have the choise during export to define the interpolation method, so you can keep the Animation Modifiers, without baking the Animation before exporting. Or maybe it would make sense to set interpolation to constant/step if there is a key on every frame.

Final thoughts: For me it is fine like it is, but when i encountert the interpolation problem it took me some time to think about a possible solution.

[julienduroure]

Hello, This case is quite interesting.

First, some note about glTF Specification :

• An animated channel can not have multiple interpolations. Only a single one
• There is no frame feature in glTF, animated channels are using seconds

So :

• A Blender curve with multiple interpolation can not be 100% compatible with glTF export
• Same for curves with modifiers like Cycle, that create (at the frame of cycling) a curve discontinuity that can not be converted into glTF

I don't think we can use check that the curve has a key on every frame, as export will convert it to second, and result will depend on the framerate.

So ... no easy answer with this case