Material Editor's feature for un-mirroring the Texture coordinates seems broken

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Hi, guys!

So, as you may know, the TexCoord node in the Material Editor has few more options if you click on the bottom arrow in order to expand its contents. One such option allows you to “un-mirror” the texture along the U, or V (or both) axis, if for some reason you need to do this to your texture. The problem, however, is that the behavior seems utterly broken:

Here’s how the regular texture looks like:

image
image1317×649 71.1 KB

And here’s what the Un-Mirror U checkbox does to it:

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image1335×654 68.4 KB

Apparently it keeps the right half of U between [0.5 … 1] and stretches it along the entirety of the domain, while discarding the left half between [0 … 0.5]. My expectation was that is should remap U from a [0 … 1] range to [1 … 0], essentially flipping it over along the U axis, as this is what “mirroring” means, at least according to my understanding, which would be the equivalent of this:

image
image1920×752 107 KB

And no, there is no problem with the texture itself. I’m using one that comes with UE and you can further see that the issue is in the UV processing if you preview the TexCoord node itself:

Regular case:

image
image932×683 114 KB

Un-Mirror U case:

image
image932×689 112 KB

It’s clear that the right side of the image gets stretched over the left one as well…

Am I wrong in my assumptions, or is this really a bug? Since even a deeper look into the documentation of this node offers me with no clue at all on why my expectation doesn’t coincide with reality.

Any ideas? Thanks a bunch!

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Ok, so… @HalukOzkul made me realize that when Epic is saying “mirror”, they do not intend to say “flipped”, but rather “bookmatched”… A simple example of that would be something like this:

image
image1800×923 199 KB

which is “mirrored” inside the texture itself, meaning the mirroring is relative to the center of the image. And if I were to “un-mirror” this image, then yes, TexCoord’s behavior now makes sense… pretty sad their documentation is not very explicit and they give zero examples of the additional node features :frowning:

That being said, I managed to actually “flip” the texture the way I initially intended to, by messing with the Tiling value and setting it to -1.0 instead of the regular 1.0, this effectively turning my image the other way around:

image

So… case solved! :slight_smile: Again, I just wish Epic would be more explicit with their intent inside the documentation, since this makes their extra features partially useless if we expect them to work in one way, yet they do completely different things, due to the developers having something else in mind, yet never bothering to explain it to anyone, anywhere…

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