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Wrong UV coordinates in Custom node


I've taken screens below in UE4.19P6 but its the same as in 4.18 also.

The problem is using this code in Custom node in the material editor

return  SceneTextureLookup(UV.xy,14,true);

doesn't give the same result as using the SceneTexture:PostProcessInput0 node.

Repro steps:

1- Create a new material

2- Change its domain to Post Processing

3- Create a new "Custom" node

4- Insert this line to it: return SceneTextureLookup(UV.xy,14,true);

5- Create a new Input for Custom node with a name "UV" and feed it with "Texture Coordinates" node

6- Create a new Input for Custom node with a name "SceneTexture" and feed it with "SceneTexture (PostProcessInput0)" node

7- Connect the Custom node's output to Materials Emissive slot

Check attached images, please.

alt text alt text


Product Version: UE 4.18
wrong.jpg (249.0 kB)
right.jpg (251.2 kB)
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asked Mar 12 '18 at 09:30 PM in Bug Reports

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avatar image Jeff A ♦♦ STAFF Mar 13 '18 at 05:32 PM


We've recently made a switch to a new bug reporting method using a more structured form. Please visit the link below for more details and report the issue using the new Bug Submission Form. Feel free to continue to use this thread for community discussion around the issue.



avatar image SumFX Mar 15 '18 at 07:43 PM

Ok done. Thanks.

avatar image SumFX Mar 17 '18 at 07:33 PM

Hi Jeff,

I think my last comment didn't arrive. Can you share my issue ID here, so I can track its progress?


avatar image SumFX Mar 26 '18 at 11:10 AM

I've sent this as a bug report, second time since I couldn't find it on Issue platform. I really don't get it why can't we able to track our reports in first place.

avatar image Jules86 Jul 21 '18 at 03:31 PM

Hi all, I'm getting this issue in UE 4.20.0 SumFX's fix still works too (which is super appreciated, thank you!)

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2 answers: sort voted first

So after hours of investigation I think I've found a workaround for this. Instead of using raw UV input inside the Custom node, you'll need to use a helper function for filtering the fed UV, So:

Instead of this:

 return  SceneTextureLookup(UV,14,true);

Use this:

 return  SceneTextureLookup(ViewportUVToSceneTextureUV(UV,14),14,true);

Still considering this as a bug though.

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answered Mar 26 '18 at 11:53 AM

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avatar image RVillani May 10 '18 at 03:57 PM

From the Developer Note on the issue:

Here the content needs to be updated to convert ViewportUV to BufferUV as FHLSLMaterialTranslator::SceneTextureLookup() does.

Like @SumFX did, Epic could at least say HOW to update the content. Or the name of the file containing the FHLSLMaterialTranslator::SceneTextureLookup() source. Because it's not easy to dig into the shader source files to find some specific method.

avatar image devast3d Jul 04 '18 at 08:59 PM

Thanks for this! I've been fighting this bug for ~2 years already and every couple of major versions Epic breaks screen texture lookup sampling. Why so is beyond my understanding (and you won't find any instructions on how to do it properly). You've saved me from headache this time.

avatar image SHADESPIRIT Jul 30 '18 at 02:30 PM

You are my hero :D

avatar image nikos_skiadas Nov 22 '18 at 07:35 AM

Really, really thank you!!

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This issue has been resolved as By Design. https://issues.unrealengine.com/issue/UE-57416

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answered Apr 12 '18 at 03:04 PM

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Jon X ♦♦ STAFF
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