Multi-Sampling don't seem to work with the Oculus SDK

[simongeilfus]

An exception is thrown when trying to set the sample count to anything higher than 1 (ex. ci::vr::SessionOptions().setSampleCount( 2 )):

11/07 16:28:26.315 {!ERROR!} [Kernel:Error] MSAA only allowed on Depth TextureSwapChains.
|error  | VrTeleportationApp::initializeVr[89] Session failed: Couldn't create texture swapchain
Exception thrown: read access violation.

[simongeilfus]

According to Oculus docs multisampling is only supported on depth textures:
https://developer.oculus.com/doc/1.5.0-libovr/structovr_texture_swap_chain_desc.html#ad4ccdb6c30c4c28e2906c9d4dd240dfc

int     SampleCount
    Current only supported on depth textures. 

Which means that we need to take care of that in the Hmd class and resolve the framebuffer attachments before submitting each frame. This doesn't seem to be optimal because of the different steps after the frame submission. As OpenGL is considered as a second zone citizen by Oculus I don't see this to change anytime soon, which is a shame! See here and there.

Just to make a quick test, I tried to add a fboFmt.samples( aboveOne ) where the fbo is created but the Fbo class fails at creating the shadow msaa target with the following ignored exception :

|warning| cinder::gl::Fbo::initMultisample[465] Failed to initialize FBO multisampling

I'll try to find out why.

[simongeilfus]

In the meantime I've added a quick implementation on this branch:
https://github.com/simongeilfus/Cinder-VR/tree/Multisampling

It leaves the ovrTextureSwapChainDesc ::SampleCount at one and creates a second multisample render target. I've not investigated yet why it doesn't work with cinder's Fbo class so I've implemented this in raw OpenGL.