Stencil Test Weirdness

I am drawing a few different passes with stencil operations that go something like -


Stencil test always, pass: replace 1
Stencil test == 1, pass: increment
Stencil test == 2, pass: increment


Stencil test <= 1, pass: keep

^ this last pass only draws over pixels with stencil value == 1. If I change it to Stencil test == 0, it will draw over the other pixels I want, but not the ones containing 1. I get the same result if I change the stencil test to < 2.

Has anyone else encountered this issue? I'm using Unity 2019 with URP.

 

I was able to get around this by changing the passes to the following -

Pass 0
Test: Always, Ref: 255, Pass: Replace
Pass 1
Test: Equal, Ref: 255, Pass: Decrement
Pass 2
Test: Equal, Ref: 254, Pass: Decrement
Pass 3
Test: GEqual, Ref: 255, Pass: Keep

For whatever reason, testing >= 255 passes when the stencil value == 0, but <= 1 does not. Weird, but I'm OK with it!

I am running into another issue that might be related though. If do the following -

Pass 0
Test: Always, Ref: 255, Pass: Replace
Pass 1
Test: LEqual, Ref: 255, Pass: Decrement

Drawing multiple objects in pass 1 on top of each other fails for any stencil value < 255. Basically, it acts as an Equal test instead of an LEqual test.

I should note that rather than explicitly setting these values in shader code, I am passing the comparisons in from UnityEngine.Rendering.CompareFunction. Should this be expected to fail?