Off axis projection with HDRP

Unity Engine
1

Hi,

I am trying to port an older project to Unity 2019.1 with HD render pipeline.

It turned out to be tricky as this project involves stereo rendering and off axis projection.
Setting a custom projection matrix seems to be impossible for Singlepass rendering however
which leads to the warning:
“Can’t set custom eye projection matrix when not in multipass mode”

As HDRP does not support multipass rendering and I am unsure if LWRP does (couldnt find a feature list)
I am curious if it will ever be possible to port to any SRP?

This leads to the following questions:

  1. Is multipass support for HDRP planned or has it been dropped (for performance/compatibility reasons)?
  2. Is it possible to support custom projection matrixes for singlepass rendering?
  3. Is there any way to tweak/customize the HDRP right now to make it work (without writing a RP from scratch)?

Thanks,
Pascal

2

Hello Pascal,

Multi-pass support for VR was recently added in the master SRP branch and will be part of 2019.3 and possibly 2019.2.

There’s currently no way to override the projection matrices for single-pass instancing but it could be added.
Could you explain your use cases so that we can come up with a good API ?

HDRP is fully available on GitHub and is C# based so that you can easily customize it or add custom features.

Cheers,
Fabien

3

Hi Fabien,

thanks for your answer.

Good to know that multipass will evetually be added.
Custom projection matrices for single pass would be great and by far the better solution for me! I was unsure if it was even possible because of culling etc.

Although I know the HDRP is public and I can customize it (which is awesome btw) I will try to avoid that as long as it isnt necessary to ensure compatibility and avoid the overhead of maintaining those changes in the future.

Speaking of compatibility we also have some problems with the current version (2017.3) like stereo quadbuffer not working with linear color space and realtime shadows being broken with custom projection matrices (just saw that my issue is marked as no fix :frowning: )
I hope that these issues may be fixed in the current Unity version but I couldnt try it yet.

If not I guess I would have to write my own shadow pass :hushed:

This is the project that I am trying to port:

https://vimeo.com/201878858

The projection matrices need to be exactly aligned in the projection surface plane for the effect to work.

Thanks,
Pascal

4

Hi Fabien. Is there currently a version of Unity/URP that gives me multi pass rendering with URP ? I need one camera per eye in my VR app and it seems only possible through multi pass…