Depth / stencil - how to communicate disabling depth checking?

[BenConMS]

D3D12 has an explicit flag (DepthEnable) for disabling depth checking:

https://msdn.microsoft.com/en-us/library/windows/desktop/dn770356(v=vs.85).aspx

OpenGL has a similar thing with GL_DEPTH_TEST and glEnable:

https://www.khronos.org/opengl/wiki/Depth_Test

And Vulkan has a bit that it sets for this too:

https://www.khronos.org/registry/vulkan/specs/1.0/man/html/VkPipelineDepthStencilStateCreateInfo.html

Metal does not seem to have a bit for this, and it appears that the NXT API is using this approach that infers disabling depth testing through the compare function:

https://developer.apple.com/documentation/metal/mtldepthstencildescriptor

I think that we have this backwards right now. This is a low-level, explicit API and having enum values side-affect into multiple settings is undesirable.

This came up when wiring up depth / stencil to the D3D12 backend, filing an issue to discuss how to proceed.

[Kangz]

The same implicit optimization of the state vs explicitly enabling things will happen for independent blend states. In PR #103 we have it implicit, but when we revisit this issue, we should handle independent blend state the same way we do depth testing.