[4.15 p2] MSAA and Alpha2Coverage problem
The forward renderer is really awesome. But with MSAA and masked materials, too much of the texture is masked out by default. It is worse with 2x MSAA than with 4X.
Here is an image using the UE4 VR template and Epic assets to illustrate the problem.
To fix this, the opacity mask clip value has to be lowered by a significant amount. So i ended up with a workaround. Changing the DiscardMaterialWithPixelCoverage fuction in MaterialTemplate.usf to adjust the clip values globally, when MSAA is on. Scaling MaskClip by 0.1 fixed the issues.
I'am not sure if this is a bug, but it would be good if this would somehow work by default, so that masked materials look the same with all Anti-Aliasing methods.
Brest Regards Michael
This is a workaround to help with the visual banding that appears when using MSAA and Alpha to Coverage, but perhaps it will also help with the masking issues here?
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.
There are no updates to this issue as of now, but it is on our roadmap to be improved.
answered Jun 15 '17 at 07:10 PM
Alpha to coverage in the forward renderer with MSAA is indeed a new supported feature in 4.15. Thanks for pointing out the coverage difference vs non-MSAA. We'll investigate and find a solution for this. I don't know when we'll get to it though.
answered Feb 06 '17 at 08:15 PM
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