So I wanted to modify the VrCuvbeWorld_Vulkan sample provided on the facebook website: https://developer.oculus.com/documentation/native/android/mobile-vrapi/ to add a geometry shader for the Oculus Quest 2. However when I tried to enable the multiviewGeometryShader feature, I was granted by a VK_ERROR_FEATURE_NOT_PRESENT error. And on http://vulkan.gpuinfo.org/displayreport.php?id=10024#features_extensions the feature is said to not be supported.
I just need a geometry shader to calculate a value for each triangle. What would be a viable alternative? On http://vulkan.gpuinfo.org they say that the geometryShader feature is supported. Therefore, is rendering eye by eye without the multiview extension a possible solution ?
If a device supports geometry shaders and also VK_KHR_multiview, that doesn't mean that both can be used in conjunction. That only works if the multiviewGeometryShader property is true. When we looked at this in detail last year, we couldn't find any device (besides some NVIDIA Quardo, I think) that supported multiview with geometry or tessellation shaders.
That means that you'll not be able to use geometry shaders with the VK_KHR_multiview extension for now. A good alternative could be to use geometry shader instancing and use the geometry shader instance's invocation id to direct rendering into different layers:
gl_Layer = gl_InvocationID;
We have actually written a paper about different variants for multi view rendering in 2020: Fast Multi-View Rendering for Real-Time Applications. The geometry shader instancing variant turned out to be one of the most performant alternatives. We only analyzed desktop, though. Performance characteristics could be different on mobile.