Eye stencils about lovr

[bjornbytes]

Two approaches I'm deciding between.

• Flexible. lovr.headset.getHiddenAreaMesh returns a Mesh and you can do whatever you want with it (render to stencil buffer, depth buffer for z prepass, custom hit tests, etc.).
• Fixed. There's just a conf.lua flag or a lovr.headset getter/setter that is like "hey do the hidden area mesh thing" and it'll render it automatically at the beginning of a frame.

Also unsure if I like using the depth buffer or the stencil buffer for this.

[bjornbytes]

I think it needs to at least be exposed (flexible) so that you can use it if you're doing a custom Canvas setup or want to decide between depth/stencil masking. Might expose it as a pre-rendered Texture, because lovr.graphics.fill is a little easier to work with than a Mesh.

[bjornbytes]

Monitoring https://github.com/immersive-web/webxr/issues/463

[bjornbytes]

lovr.headset.getDisplayMaskexists!