[ModelDoc] AnimStartLoop unexpected/undesirable behavior with ExtractMotion

Grodbert commented 1 year ago

Describe the bug

When using both AnimStartLoop and ExtractMotion nodes, they yield the undesirable effect of first Offsetting the start of the animation, and then Extracting the motion, causing any "movement" animation to start offset

Changing the order of the nodes doesn't do anything.
Adding an AnimAlign is a good "workaround"

To Reproduce

Create a model with an animation that moves the model around
Extract its motion by adding "Extract Motion" to the simple animation
Add an "AnimStartLoop" node and give it a high frame number (but not last frame)

I've left a "quick" repro file, just drop it in any project/addon's folder as is.

Expected behavior

The motion should be extracted first, and then AnimStartLoop should start the animation from the desired frame, allowing for quick editing of animations that do not match when blended. (aka the [supposedly] intended use of AnimStartLoop)

Media/Files

https://github.com/sboxgame/issues/assets/86626409/6039e75d-5eea-411e-92f9-5b7bbaf51407

repro.zip ^ Repro, in case needed

Additional context

I am not sure this is a bug, it seems to be the logical result of first applying the "AnimStartLoop", making the animation start offset, and then applying the "ExtractMotion", hence why the treadmill is offset.

Personally, I think the nodes should be applied the other way around, if possible (allowing you to easily fix any syncing errors in movement blends, which are very finicky to get right), since "AnimStartLoop" was likely made for this use, as its description is:

Resets the starting frame of a looping animation. This is useful when mixing multiple animations and the animations need to all run together in phase, but the source animations don't match.

So it wouldn't make sense for the 2 modifiers to conflict in such a way when they'd be commonly used together for this purpose.

Although, I leave the decision to any dev picking this, as using AnimAlign mostly fixes this, however, I assume this creates more chagrin than having it the other way around.