RemoteTransform2D scale only with global coordinates enabled is wrong

[mrcdk]

Godot version:

3.2dev, 3.1.1, 3.1, 3.0.6 and maybe others

OS/device including version:

Windows 10

Issue description:

Looks like when you get the scale from a Transform2D the coordinates it uses aren't the ones one would expect as per issue #21020

This makes the RemoteTransform2D scale behavior when its use global coordinates enabled (the default) and only the scale selected to behave unexpectedly

Steps to reproduce:
Check the MRP

Minimal reproduction project:

remotetransform2d_scale_issue.zip

[mrcdk]

@reduz answer:

[13:20:44] <reduz> mrcdk: the problem is that if you mirror one of the axes,  you break rotation decomposing
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[13:27:57] <reduz> mrcdk: and also, if you think about it logically, there is no way to tell which axis was scaled if you look at the matrix
[13:32:34] <mrcdk> yeah, makes sense
[13:34:24] <mrcdk> how could RemoteTransform2D be fixed though?
[13:37:45] <reduz> mrcdk: if you are just using rotation, scale and translation it should just work because it sets a transform directly right? so I assume it breaks when you dont use one of the transforms
[13:38:17] <mrcdk> yes, it breaks when using only the scale
[13:40:12] <reduz> ahh, it makes sense, i dont really know how this can be fixed
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[13:42:05] <reduz> maybe somehow documentation should be written to specify that if your source node in global transform uses a negative scale in either x or y, in global coordinates, it is not possible to mathematically infer how to apply that scale in the destination node
[13:42:15] <reduz> we could even use a node warning also (using get_configuration_warning()
[13:43:04] <reduz> so you can tell something is broken the moment you apply it

[KoBeWi]

Can anyone still reproduce this bug in Godot 3.2.3 or any later release?
(I checked the MRP, but not sure what to look at)

[akien-mga]

The MRP still behaves as in the OP. As per #31260 (comment), the solution seems to be to write some documentation to warn users about this.