Animation track with UpdateMode set to Discrete are not reset by the Deterministic option

[kaluluosi]

Tested versions

Godot Engine v4.5.1.stable.steam.f62fdbde1 - https://godotengine.org
Vulkan 1.4.312 - Forward+ - Using Device #0: NVIDIA - NVIDIA GeForce RTX 4090

System information

Godot Engine v4.5.1.stable.steam.f62fdbde1 - https://godotengine.org Vulkan 1.4.312 - Forward+ - Using Device #0: NVIDIA - NVIDIA GeForce RTX 4090

Issue description

1.mp4

default.mp4

I am developing my action game, and I want the current attack action to be interrupted when the character is hit.

Then I found that if I call animationplayer.play("hurt") to interrupt the current animation and play a new one while the current animation is playing, if the attack hitbox is still active when it is interrupted, the attack hitbox will remain active.

After my tests, I suspect that the deterministic property of AnimationPlayer only performs the RESET operation when the animation is completely finished, that is, when the animation_finished event is triggered.

If this is the case, there is a big problem: the animation properties cannot be properly cleaned up and reset when the action is interrupted.

Steps to reproduce

1.mp4

Minimal reproduction project (MRP)

animation_reset.zip

[TokageItLab]

Several setup configurations are odd:

1. When UpdateMode is Discrete, resets by the Deterministic option do not occur

I assume this lacked from the documentation (so this is documentation issue). Then you must either set UpdateMode to Continuous or set CallbackModeDiscrete to ForceContinuous if you want to reset by Deterministic option.

2. Deterministic resets depend on the RESET animation

Even if set to Continuous, since RESET animation has Disabled set to false, it will reset to false, so you must key true in RESET animation. Also, with Continuous, the first key is always processed, so you must add the key at frame 0 to attack animation.

The project with recommended settings applied is as follows.

animation_reset_fixed.zip

[kaluluosi]

I tried the suggestion above to set UpdateMode to ForceContinuous, and it seems to work.

109.mp4

My attack box finally got reset when it was interrupted by a hit.

However, I still found a minor issue. That is, my attack animation has a bool property track called interrupt_window, which is used to determine whether the current state allows immediate interruption to the next state. This allows players to input in the last few frames of the animation to immediately interrupt the current action and switch to the next action, thereby achieving Combo Attacks.

When the attack animation is playing, I noticed that

110.mp4

Also, with Continuous, the first key is always processed, so you must add the key at frame 0 to attack animation.

So regardless of whether it is reset or not, it is best to set a keyframe for the state of the attack box to reset it to the initial state on the first frame of all animations?

111.mp4

Summary

1. If users want some property tracks to be automatically reset using RESET when switching animations, they must enable the Deterministic option of the AnimationPlayer. Typical application scenarios include controlling the activation/deactivation of CollisionShape or the active state of particles for precise control in animations.
2. The Deterministic option only affects tracks with UpdateMode set to Continuous and has no effect on Discrete tracks.

However, boolean property tracks are often the ones that need the Deterministic feature the most, yet they are more suitable for working in Discrete mode.

This is because if a boolean property track operates in Continuous mode, there will be an odd behavior.

For example, no key is set at frame 0, True is set at frame 10, and False is set in RESET.

When switching animations, the boolean property is reset to False by the Deterministic option. But surprisingly, when the animation is actually played, even though no key is set at frame 0 (which should logically retain the RESET value of False), it is inexplicably set to True. (It seems that continuous tracks for boolean values treat booleans as floats for interpolation, incorrectly interpolating the value to True?)

To avoid this strange phenomenon, you must add a key at frame 0 of the boolean property track to set the initial value. In this case, the boolean property track essentially cannot utilize the Deterministic feature at all.

In any case, the behavior of boolean property tracks in Continuous mode is somewhat unpredictable. This inconsistent behavior requires additional tricks to fix.

[TokageItLab]

To avoid this strange phenomenon, you must add a key at frame 0 of the boolean property track to set the initial value. In this case, the boolean property track essentially cannot utilize the Deterministic feature at all.

This is incorrect. For example, when playing an animation that lacks a Boolean track, if the RESET animation possesses a Boolean track, it will reset the animation to that key value during playback.

In other words, the Deterministic option is equivalent to Unity's “write default” option.

When switching animations, the boolean property is reset to False by the Deterministic option. But surprisingly, when the animation is actually played, even though no key is set at frame 0 (which should logically retain the RESET value of False), it is inexplicably set to True. (It seems that continuous tracks for boolean values treat booleans as floats for interpolation, incorrectly interpolating the value to True?)

This is not strange. Continuous mode constantly writes some value. Unless loop wrap is enabled, the first key is retrieved. This behavior matches most video editing software and DCC software timelines.

While it might be theoretically possible to add a RESET mode to loop wrap to enable complementing with the RESET key, it ultimately same with to adding a key to the first frame. If deterministic reset is required, this would likely be a restriction.

If you wish to reset values without using deterministic while maintaining Discrete behavior, the following function should work:

func play_with_reset(animation):
	AnimationPlayer.play("RESET")
	AnimationPlayer.advance(0)
	AnimationPlayer.play(animation)

[Mopzilla]

func play_with_reset(animation):
	AnimationPlayer.play("RESET")
	AnimationPlayer.advance(0)
	AnimationPlayer.play(animation)

I am inexperienced with Godot's animation system, but I don't believe it is simple to implement a workaround like this when using AnimationTree.

This is not strange. Continuous mode constantly writes some value. Unless loop wrap is enabled, the first key is retrieved. This behavior matches most video editing software and DCC software timelines.

While it might be theoretically possible to add a RESET mode to loop wrap to enable complementing with the RESET key, it ultimately same with to adding a key to the first frame. If deterministic reset is required, this would likely be a restriction.

Does this mean #113260 will never be "fixed" and will always require a workaround on the part of the developer?

[TokageItLab]

@Mopzilla Think of it as a specification rather than something to be fixed. Users need to understand the difference between Discrete and Continuous, what happens with Deterministic, and the implications of each combination.

However, indeed it is lacking sufficient documentation, so we plan to prepare some tutorial material.

Well, if we were to implement something besides documentation, I think we could add some helper functions like AnimationMixer.reset() and AnimationPlayer.play_with_reset() function that calls the reset in one line. Since we have revised the behavior of Discrete and Deterministic many times in the past and added some options for that, I believe there is almost nothing more we can support.

[Mopzilla]

AnimationMixer.reset() would be an amazing function to have, and is definitely a solution I would love to see.

I agree on the lacking documentation, Godot's built-in animation implementation is very large and complex. I don't personally have any idea how all the different modes like recessive, discrete, force_continuous, etc work. I just use what I am told to use or what works.

[TokageItLab]

@Mopzilla FYI, this is the only article currently available on Deterministic and Discrete, but I know it needs to be properly organized into documentation later.

[ericdallo]

I just had the same issue and fixed adding a keyframe at start of attack animations to disable the hitbox even if reset was supposed to do it, spent a good amount of time until find this hack, and only now find this issue days later :)