Warn when setting a scale that has a negative X component in 2D

[aaronfranke]

Due to the way scale is represented with Transform2D, negative scales on the X axis will be changed to negative scales on the Y axis plus a rotation of 180 degrees when decomposed.

Because of this, we should show a warning. Fixes #17405 and its duplicates #21020, #21849, and #42219.

[realkotob]

I don't disagree with adding a warning, but it should be clear why this is important for the user to know, or else it just seems like a technical comment you'd find in engine code.

It should explain the end result on the user side, even briefly, or else it's just noise.

[groud]

I don't think this warning is a good idea, you might use an x negative scale on purpose.
Such warning would be really annoying.

[aaronfranke]

@groud We still need a way to inform users that negative X scales aren't treated as such internally, since many users ask for help about this and many issues have been opened about this. Do you have another idea on how to warn users? Perhaps the warning should be able to be disabled in the editor settings?

Also, there are still ways to use a negative X scale on purpose without a warning. Maybe I should have been more explicit with the description. This doesn't show any warning when doing t.x *= -1, since setting t.x is a reliable way to change the X axis (and if you choose to decompose that, it will silently decompose into a rotation of 180 degrees and scale of (1, -1)).

[groud]

No, even if it's possible to disable it I don't think it is a good idea.

I believe stating that in the documentation should be enough.

[aaronfranke]

@groud Where in the documentation should this be stated? I'm not against a solution that only involves documentation changes.

[groud]

I'd say in the reference, for the scale property of Node2D ? And maybe in the Transform2D reference too.

[ghost]

There was this suggestion:

Maybe it would just be better to have .global_scale and .global_rotation calculated directly from the stored values instead of using the transform2D?

Or maybe we could add separate functions to retrieve the true scale and rotation.

I never saw any discussion in this direction, wondering if or why this isn't a viable solution?

[aaronfranke]

I still think a warning is a good idea, but I just updated this PR so that there's a setting to disable the warning.

[reduz]

I dont think this PR makes much sense, Godot 2D nodes dont store tranforms but loc/rot/scale, so negative scale is fine. The only situation where this may work is whether for some reason in the editor the global transform is modified but I am not sure in which case this may happen.

[Zireael07]

The OP lists four reports of what seems to be the same issue this fixes.

[aaronfranke]

@Zireael07 Thanks, I went through and ensured they were closed appropriately. For reference, they are #17405, #21020, #21849, #31980, #42219, #62544, and #62663.

[Zireael07]

Whoa, that's even more multiplicates than I thought. So it's not something once in a blue moon - I think the PR should be reconsidered.

[KoBeWi]

Yeah I myself closed a few of such reports. But if we go with a warning, there should be a way to disable it. It's only meant to inform the user about the unexpected behavior; if you know it, the warning is useless and annoying.

[aaronfranke]

@KoBeWi That's what this PR does.