VisGL depth buffer

Testing the VisGL device with our example code, we found that the depth values wouldn't behave as expected (or, e.g., as the depths provided by the "visrtx" device do). According to @jeffamstutz the depth values returned by ANARI are supposed to be linear, and should originate at the camera position. For interop with OpenGL, our app therefore transforms these depth values to GL window coordinates (cf. this code).

So I'm wondering if the depth values that the "visgl" device generates are already in window coordinates (which to my understanding they're not supposed to be, according to the specs). Could you please clarify what the format is of the depth buffer obtained by VisGL? (for spheres and cylinders I found fragment shader code that I'm quite sure generates depth in WC, but have a bit of a hard time following what the triangle object shaders do.)

Reproduce the depth output with the VisGL example code, then inspect the sphere and cylinder fragment shaders and the triangle object shaders mentioned in the issue. Compare their output with the ANARI linear, camera-origin depth expectation and the conversion in Projection.cpp; done means the depth-buffer format is clarified and behaves consistently with the specification.