Oh my stars and garters!
I was so excited I never realized you were doing the stereo that way! I thought LilyRender handled the stereo problem not monoscopic cubemapping. I had no idea Unity sucked at that.
So - stereo cubemap problems - I know them well. Me and those seams have gone to war to bring 3D VR to Blender Eevee via the same cubemap trick you are doing in Unity.
I fell from my chair when I first saw @CouchOimoSp (on Twitter) figured out how to win the war.
This simple mask.
View attachment 76437
If you speak node tree at all from any rendering system you should be able to follow this ...
View attachment 76438
The big top box is an image of the front cube face.
The UV map gives it a place to sit on the cube face.
That image is made emmissive - ergo a film projector.
That image is sent to a mix shader - bookmark that for a moment
In parallel - The same image is sent to mix shader that is combining color with transparency (opacity?).
The amount the image is being made transparent being controlled by the alpha channel of the mask . (That means you don't want to lose the alpha channel of the image.)
And now what that node tree actually does ...
The side of the cube the camera is point at is pushed in towards the camera. A pushed in rectangle like this still becomes part of a sphere so translates appropriately in the projection from a globe to equirect.
As you get closer to the edges of the front face it starts projecting less light while at the same time allowing more light to come in from behind. The light coming in from behind is the same "eye" of different cameras. One cube face camera's left-eye combines light with another's left eye while always maintaining the same total light intensity reaching the panoramic camera inside the modified cube.
If you look at the image of the projection boxes showing the projected images you can see that where the left face interlaps with the front is where the seam was at the bookshelves. That's now overlaping with one left-eye's perspective on the bookshelf (literal use of the word) melding with the other's.
The vertical ones were the most noticeable but you also get sliding shifts at the ceiling and floor if you want looking up and down to be stereo. A carpet with prominent circles like that one made the shift stick out (from a different angle). This mask trick applies to all 4 edges of the front face.
(Question for the class - where are there still minor seams that can't be fixed?)
How you translate this magic into Unity? I'll be buggered if I know - but you should be able to understand what the light is doing and that's the main thing.
Hope it helps!
Even with the wrong stereoscopy this is still perfect for my own selfish needs.
I have never put anything of interest far enough at the sides to notice loss of stereo vision.
You're already my hero and making it more true every update.
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Credits not mine ...
The "Mr. Elephant" blend file is one of the Eevee demo files created by By
Glenn Melenhorst .
It was never intended to be used for VR - which made it perfect to show both what VR can do and what freaking Glenn can do. He took no shortcuts.
Home of the Blender project - Free and Open 3D Creation Software
www.blender.org
So yeah ... VAM is not the first place I've shamelessly repurposed other people's non-VR work.