Stereo Layer Transparency broken for UI Widgets on Quest

[leftbigtoe]

To improve the quality of our in game UI, we recently moved it from world space widgets to Stereo Layers.

However, transparent Stereo Layer have black backgrounds on the quest where it is supposed to be transparent.  After setting up the stereo layer, so that it gets live textures from the Unreal UMG system, the transparent parts appear black on the Quest.

So here how it looks on the Quest:


And how it looks on the PC with oculus link and VR preview in engine (this is how it is suppose to look): 


 The issue only pops up with Live textures, if I place a sprite with alpha channel as the texture, it is displayed correctly with alpha blending.

One thing we have already tried is creating the render target in C++ and ensuring that the clear color has the alpha of 0, so (0,0,0,0) and the format supports RGBA.

We are on Unreal version 4.25.3 on the Oculus Unreal Branch built from source.

Any tricks to get this working? Thanks for the help!

Daniel

[rpalandri]

The issue here seems to be (at least I think trying to repro this on my end) not the live texture portion of this (transparent live textures stereo layers seem to work fine), but the fact that you checekd SupportDepth (which in the current implementation doesn't support transluency). Can you confirm?>

[Mohammed_hashim]

Are you sure its not supported? I'm using masked 3d widget and having the same issue with Oculus Quest.

[Joejoe0707]

@rpalandri where you ever able to solve the "world renders black" bug in 4.26 if support depth  is checked on a stereo layer?

I posted a question on UDE about 6 months ago.

[Mohammed_hashim]

No fix for it since Oculus team replied to my email that this feature doesn't exist, a big shame to hear that,
auzden shared a workaround to add this feature but it will require source engine modification and only works on Vulkan.  not sure about the performance impact or any other side effects. so do it on your own risk. 

 https://github.com/auzden/UnrealEngine/commit/9f8c34faaefcf8a66ab317a48e938b8c1185ca6f

[CarpetFace]

I ran into this problem too.  While playing around with things, I edited my Widget BP's design to have a transparent background, instead of trying to have my material control the opacity, and the transparency for the Widget's RenderTarget correctly shows up on as transparent.

I hope that helps someone!

I'm still fighting two losing battles.  I want my stereo layer to still do depth testing, and that isn't working for me, as it always renders on top of everything.  I'm not sure if that is by design, current limitation, or I am just missing something.  While trying to get it to work, I noticed that I can't get the material used by the Widget to ever affect the Stereo Layer.