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Texture issue while using another UV channel

Hi! I'm making a birch tree, and after looking at the Open World Demo trees I found that they used a clever way of adding moss at the bottom of the tree. On my birch tree, I wanted to use the same method to add some dark bark on the bottom of my tree.

So I opened my tree in Maya and added an empty UV channel, and cylindrical mapped only the bottom part of the trunk. In my bark material in UE4, I then added a dark bark texture with a mask in the alpha, and set it up to use the correct UV channel, as you can see in the images I included here. I set it up pretty the same way they did in the Open World Demo. When I do so, the bottom part of the tree works fine. However, every part of the trunk that does not have UVs in the channel I added, gets dark. I've included an image that shows the difference between my mask material setup and a material with only the birch color. I'm only using movable lights, so I don't think it's a lightmap problem. Any ideas?

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Product Version: UE 4.10
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asked Jan 13 '16 at 12:44 PM in Using UE4

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JakobBergersen
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That is rather... odd.

Thinking of a workaround. Could vertex paint the bottom, or perhaps multiplying the bottom bark texture with the alpha and then adding the base bark with the output of aforementioned multiply. Though.. that might also cause some issues.

Does seem to be a bug, or worst case scenario.. the black in that mask.. isnt 100% black, though I am sure you double and even triple checked that.

Edit: also, double check that the lightmap channel isnt set to one of your texture channels.

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answered Jan 13 '16 at 01:47 PM

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Luos
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avatar image JakobBergersen Jan 13 '16 at 06:41 PM

Thank you for the quick reply!

Your second workaround gets me the same issue. Vertex painting works though, and I will probably use that as a workaround if I can't figure out what's causing the issue. So thank you for that suggestion!

The black in the mask is 100% black, though I've heard that UE4 sometimes make value corrections on the import, although I'm not sure exactly how this works. I've read that this can be accounted for by having the mask in its own texture and changing its compression settings to Mask, though it didn't help in my case.

As you said, it might just be a bug. Any advice is still greatly appreciated!

avatar image Luos Jan 13 '16 at 07:20 PM

Ill have some time tomorrow to test it, only thing I can think of on the top of my little head is, if the texture is set to SRGB, it might do something with the gamma? perhaps multiplying the alpha, power node, or something similar might help.

avatar image JakobBergersen Jan 13 '16 at 10:30 PM

It seems like what caused the problem was pretty much the absence of the rest of the tree in my UV channel. I didn't think it would be a problem, seeing as I only really needed the bottom of the trunk. Anyway, I brought the rest of the trunk into the UV channel and simply squashed everything together except for the bottom of the trunk, and that seems to have solved the issue. Yay! I've included an image of the UVs to show what I mean.

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avatar image Luos Jan 13 '16 at 10:52 PM

aaaah, yea that makes a lot of sense! thanks for showing :)

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