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Issue with masked materials (Forward rendering + MSAA)

I'm having issues with a masked materials on forward shading and MSAA. All masked materials become translucent. I have no problem with MSAA and deferred rendering.

With MSAA:

alt text

With TAA:

alt text

You can reproduce it in Material_Properties map (Content Example).

Product Version: UE 4.15
msaa.png (81.4 kB)
taa.png (54.1 kB)
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asked Feb 22 '17 at 10:05 PM in Bug Reports

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avatar image michaeleeli Feb 02 '18 at 06:39 AM

In your picture, the side of the material has artifact lines due to MSAA. Do you know how to work around that?

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Hey amasnyi,

Thanks for the clear and precise repro steps. I was able to confirm what you are reporting and have gone ahead and entered a bug report for the issue. You can track the report following the link below on our public issues tracker.


Once the issue has been addressed by our engineers the ticket will be updated and reflected in the public tracker. Let me know if you have further questions or need additional assistance.


Andrew Hurley

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answered Feb 23 '17 at 05:12 PM

avatar image DanielW STAFF Feb 23 '17 at 06:52 PM

This is how AlphaToCoverage works. Your opacity mask becomes an MSAA coverage value, which allows anti-aliasing of the mask.

To get a result closer to the deferred renderer, you can make your OpacityMask input into a steeper gradient. For example if you have an OpacityMaskClipValue of .33, you can do a Mul with 5 and then Subtract (.33 * 5). This will make the OpacityMask gradient steeper, pushing the translucent bands closer together, but keeping the value .33 in the same spot.

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