Low priority continuation of #122

These need additional handling:

• ViewRenderManager needs to support depth buffers so the alpha mask can be generated
• There's something special with third-person mode that needs researching. It seems to partially by-pass our view/model matrix overwrites.
• BP's occlusion culling gets confused when there are multiple (external, i.e. multiple calls the EntityRenderer.updateCameraAndRender) render passes with significantly different views because it thinks those are for different frames (if I'm not mistaken, you can actually still reproduce this by having a portal only be visible in one eye)

Until then, portals are disabled for the third-person pass (ref).

So for clarification, the "first person" render pass (which is still a third render pass, just from the center HMD perspective) works, correct?

So for clarification, the "first person" render pass (which is still a third render pass, just from the center HMD perspective) works, correct?

Yes (at least at time of issue creation, haven't tested since).
There should be no issue with a third render pass (or really any number of render passes), it's just the depth buffer and third-person offset which aren't working yet (the latter being why I completely disabled BP's rendering during the third-person pass for now).

Edit: Reading one of my comments at the time, there's also an issue with BP's occlusion culling which I forgot to list in the above issue (just added it), that's another reason why BP's rendering is disabled during the third-person pass.