[Feature request] Back-face culling

[stukowski]

It would be very useful if OSPRay could support back-face culling for mesh faces in the future. What I am asking for is an option similar to VisRTX's experimental cullBackfaces option, which can be set on ANARI triangles geometries.

A typical use case would be rendering two-sided meshes with differently colored front and back sides of the surface. Such meshes consist of pairs of faces with opposite winding orders, and back-face culling would allow only one of the faces to be visible (the front-facing one). An example:

Currently, rendering of such two-sided meshes can only be realized by performing the (view-dependent) back-face culling on the application side prior to handing the filtered face list to OSPRay.