Translucent render order of refractive materials

anonymous_user_034cecd6 · December 22, 2015, 10:37am

Hello,
I found a problem that the translucent-refractive material may be rendered in wrong order. The refractive object is somehow always rendered on top of the translucent but not refractive objects. Do we have any methods to avoid this ?

Refractive Materials

White Translucent Material

Black Translucent Material

anonymous_user_cc69b907 · December 23, 2015, 3:49pm

Hello ,

This is to be expected. Translucent materials are rendered in order based on the position of the camera. We sort translucency per draw call by camera distance. Per Pixel would solve this but it’s very expensive and we do not support that yet.

If you navigate to the other side of the white cube is the non refractive material not on top of the refractive material?

anonymous_user_034cecd6 · December 24, 2015, 2:25am

Here is is the result of viewing these objects from the other side.
The translucency sort priority of each object is set to 0.

anonymous_user_cc69b907 · December 29, 2015, 3:51pm

Thank you for providing the screenshot. I will test this and attempt to recreate this issue on my machine.

anonymous_user_cc69b907 · January 4, 2016, 3:20pm

Interesting, I have been unable to reproduce this issue on my machine. The refractive material does not take priority over the non refractive ones.

Front :

Back :

Would you provide your DxDiag ( System Specs ) so that I may investigate any hardware related issues.

anonymous_user_034cecd6 · January 5, 2016, 11:25am

Thank you for testing.
my dxdiag:
[link text][1]

and by the way, my “separate translucency” is set to false. If it is set to true, the result will be the same as you.

Do we need to turn this option on to get the correct transparency order ?

Lovecraft_K · January 6, 2016, 5:08pm

Hello -

I have entered a bug report for this particular issue as UE-24998 and will keep you informed here as we investigate a solution to this issue. In the meantime as a workaround you can leave separate Translucency on and in the materials remove separate transparency per material which would allow you to keep the sorting.

Thank You

Eric Ketchum

MaverickAl · September 2, 2019, 6:30am

I noticed that this bug is now listed as won’t fix; although I can’t see any explanation on the bug page.

Since the most common use case for refraction is on waters surface (which if anything you would want rendering before any other transparency) I’m assuming there must be some work around?

JDARRAS · April 23, 2022, 4:30pm

Thanks a lot for “translucency sort priority” I didn’t know and this fix my problem !