New forward rendering artifact when used with VR instanced stereo

Development Platform & Builds XR Development
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1

This is probably a known issue internally but just in case it’s not I have noticed weird darkened tiles for the right eye when attempting to used VR instanced stereo on the github master/promoted branches for the upcoming 4.14 release.

It’s hard to see in the provided screenshot but it’s pretty obvious when actually using an HMD. You have to compare the areas circled for each eye rendering to notice the difference. The left eye seems correct but the right eye has certain quad areas on the screen that are darker than they should be.

2

Hello tmek,

I have a few questions for you that will help narrow down what issue it is that you are experiencing.

Quick questions:

  1. Can you reproduce this issue in a clean project?
  2. If so, could you provide a detailed list of steps to reproduce this issue on our end?
  3. Could you provide screen shots of any blueprints/settings that may be involved in this issue?
3

Hi Rudy,

I was able to reproduce this fairly easily. If you have a stationary point or spot light and look at it from a distance as shown in this video. (look in the right eye view at the point light shading on and surrounding the UE4 mannequin)

I’m assuming the forward shading is using a tiled rendering technique. It seems that in this situation, for only the right eye, certain tiles are not including the point light’s contribution to the scene.

Here are the steps to recreate:

  1. Create a new project based on third person template.
  2. turn on forward shading, stereo instancing and MSAA in project settings.
  3. select the “ThirdPersonCharacter” actor in the scene and disable auto possesion.
  4. open “ThirdPersonGameMode” blueprint and set default pawn to DefaultPawn. (#3 and #4 will allow us to fly around the level freely)
  5. put a stationary point light right next to or a spot light shining down on the mannequin.
  6. run in VR mode and fly out as shown in the video above.

The left eye seems to render correctly but the right eye gets these weird darker squares/tiles around the areas lit by stationary point or spot lights.

(I should also point out that I’m using an Oculus CV1 if that makes a difference.)

Here’s a cropped comparison screenshot zoomed in. Again showing the right eye rendering has some squares or tiles not rendering a stationary light’s (a spot light in this case) influence correctly.

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4

Hello tmek,

After running a few tests and doing some digging I found that this is a known issue (UE-36114) that has been submitted to the developers for further consideration. I will provide updates with any pertinent information as it becomes available. Thank you for your time and information.

Make it a great day

5

Thanks Rudy :slight_smile:

Is answerhub the place to provide feedback on issues in promoted or master builds or is there a more appropriate place to do that?

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If you have issues when using the engine and you feel that you have encountered an issue, this is the place that you will want to go for assistance.

8

interesting. I was running a test with the built in Custom Water Mesh Actor and the default material. I am getting huge black artifacts, but only when using that shader.

I am not sure if the shader is just not working with forward shading, or if this is kinda related.

Anyone else experiencing the same problem?
thank you so much