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How to correctly use SRGB on Oculus Mobile Native (C++)?

mccmcc Posts: 36
Brain Burst
This is a Go+Quest question. I have a Oculus Mobile C++ app forked from the VRCubeWorld_NativeActivity example in the Oculus Mobile native SDK. I hooked in my own code in `ovrRenderer_RenderFrame`, so right after the framebuffer and the eye matrices are set up I call my own rendering code. This rendering code is shared with desktop, it enables `GL_FRAMEBUFFER_SRGB` and it exclusively draws the SRGB color space.

I am trying to figure out how to convert VRCubeWorld_NativeActivity from RGB to SRGB. I want the SRGB drawn by my rendering code to be correctly treated by the NativeActivity.cpp's framebuffer and EGL surface. I have found a way that "works" (I see the colors I expect) but I do not know if it is correct. You can see my exact NativeActivity code here (it is open source).

What I did:
  • Pass `GL_SRGB8_ALPHA8` instead of `GL_RGBA8` in ovrFramebuffer_Create
  • Set `VRAPI_MODE_FLAG_FRONT_BUFFER_SRGB` in `parms.flags` when we call `vrapi_EnterVrMode`()
What I did NOT do— because I tried these things and they had no effect:
  • Call `setEGLattrib(EGL_GL_COLORSPACE_KHR, EGL_GL_COLORSPACE_SRGB_KHR);` after calling `eglCreateContext()` (I think we do this in our glfw version, and it is recommended in a long comment in VrApi_Types.h).
  • Comment out the many `VRAPI_FRAME_LAYER_FLAG_INHIBIT_SRGB_FRAMEBUFFER` lines left over from the sample code.
What I need to know: 
  • Am I doing something wrong or unsafe, or incurring any penalty (like unnecessary conversions RGB->SRGB and back again) by failing to explicitly set the EGL_GL_COLORSPACE_SRGB_KHR egl attrib?
  • What do the various VRAPI_FRAME_LAYER_FLAG_INHIBIT_SRGB_FRAMEBUFFER flags do? What does this "layer" code (the "black layer" and "loading icon layer") do, and can I safely remove it? (I have removed a lot of the code from the NativeActivity example because I was sure I did not need it, but there are other parts I did not understand so I have left it in. Because there is not really any comments/documentation on the sample code it is hard to tell what is necessary and what Oculus merely left for us as a convenience.)
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