4.0 Alpha 5 regression: Color blending with alpha channel by AnimationTree is broken

[jcarlosrc]

Godot version

4.0 Alpha 5

System information

Windows 10

Issue description

When using an Animation Tree it changes properties to default values after an animation is ended. As an example, in the minimal project attached:

• If we use the AnimationPlayer directly, it works as expected (transparency to 0) (first video).
• If we use the AnimationTree, it resets ColorRect to a default white (1,1,1,1) color value (second video).

This occurs for any property on any node. The problem is new, Alpha 4 did not preset it. Imported animations from Blender seems not to be affected.

BugReport02_4alpha5.DEBUG.2022-03-24.12-50-59.mp4

BugReport02_4alpha5.DEBUG.2022-03-24.12-51-21.mp4

Steps to reproduce

In the attached minimal project, enable or disable "Use animation tree" option and run the project to see the behavior as in the videos.

Minimal reproduction project

BugReport02_4alpha5.zip

[Calinou]

cc @TokageItLab

[nonunknown]

just a question, the animationplayer in question was made local?

[jcarlosrc]

just a question, the animationplayer in question was made local?

Yes, animations were made inside Godot. Those are which have the problem.

[jcarlosrc]

It is a simple animatio

just a question, the animationplayer in question was made local?

Yes, animations were made inside Godot. Those are which have the problem.

It is a simple Animation Player node in main scene which changes the color of a child node, the color rectangle.

[TokageItLab]

I think this is a bug caused by Variant::zero() actually using an initial value instead of zero: we want Color(0,0,0,0) but it return Color(0,0,0,1), maybe we should create separate functions like Variant::zero() and Variant::init().

[TokageItLab]

For now, this seems to be a special case bug for the alpha value of Color. I have sent a fix so that Variant::zero() explicitly returns Color(0,0,0,0) for blending as #59490.

[jcarlosrc]

This is not exclusive of color. Animated collision shapes also go back to its default (0,0,0) position in a similar behavior.

For now, this seems to be a special case bug for the alpha value of Color. I have sent a fix so that Variant::zero() explicitly returns Color(0,0,0,0) for blending as #59490.

[TokageItLab]

@jcarlosrc Can you test #59490?

[TokageItLab]

Note: Maybe it should be noted in the documentation, if one of the two animations to be blended is lacking a track, it will be blended with the zero value. As we said #46038 (comment).

In other words, the incorrect color blending is a bug. The change in the behavior for blending lacking tracks is an ideal behavior.

[jcarlosrc]

If a track is missing in the other animation it should not be blended. This is the behavior of all versions previous to 4.0 alpha 5. Otherwise, we will need to insert a track for every property ever keyframed in any animation to avoid a bad mixing. This does not make sense.

[TokageItLab]

It creates an incongruity that the blended result will not always be the same, and we decided in discussions with reduz that it is an edge case.