Stock Unity UI Stencil usage?

Unity Engine
1

Do the default UI & mask shaders write to the stencil buffer? If so, do they use a known WriteMask and ReadMask? I see a number of stencil properties in the default UI shader.

2

I just found this for HDRP: There are 2 “User Bits”:
UserBit0: 64 (0b1000000)
UserBit1: 128 (0b10000000)


That information can be found here: Enum UserStencilUsage | High Definition RP | 8.1.0
or in an example here: HDRP-Custom-Passes/Assets/CustomPasses/SeeThrough/SeeThrough.cs at master · alelievr/HDRP-Custom-Passes · GitHub

The other bits are used by unity, which is listed here:

#define STENCILUSAGE_CLEAR (0)
#define STENCILUSAGE_REQUIRES_DEFERRED_LIGHTING (2)
#define STENCILUSAGE_SUBSURFACE_SCATTERING (4)
#define STENCILUSAGE_TRACE_REFLECTION_RAY (8)
#define STENCILUSAGE_DECALS (16)
#define STENCILUSAGE_OBJECT_MOTION_VECTOR (32)
#define STENCILUSAGE_EXCLUDE_FROM_TAA (2)
#define STENCILUSAGE_DISTORTION_VECTORS (4)
#define STENCILUSAGE_SMAA (4)
#define STENCILUSAGE_WATER_SURFACE (16)
#define STENCILUSAGE_AFTER_OPAQUE_RESERVED_BITS (56)
#define STENCILUSAGE_USER_BIT0 (64)
#define STENCILUSAGE_USER_BIT1 (128)
#define STENCILUSAGE_HDRPRESERVED_BITS (63)

These values can also be found in the internal enum: “UnityEngine.Rendering.HighDefinition.StencilUsage” which you can decompile by ctrl-clicking the word “StencilUsage” in Visual Studio.