Bug Metal shader stripping removes fog for some multi_compile combination | Unity 2021.2.8

Seeing very odd behaviour with SSAO and FOG and the use of multi compile.

I have a v basic shader

Code (CSharp):

1. Shader "SSAO_FOGtest"
2. {
3.   SubShader
4.     {
5.         Tags {"RenderPipeline" = "UniversalPipeline" "RenderType"="Opaque" "Queue"="Geometry" }
6.      
7.         Pass
8.         {            
9.             Name "ForwardLit"
10.  
11.             ZTest LEqual
12.             Blend One Zero
13.  
14.             HLSLPROGRAM
15.  
16.             #pragma multi_compile _ _MAIN_LIGHT_SHADOWS _MAIN_LIGHT_SHADOWS_CASCADE
17.             #pragma multi_compile _ _ADDITIONAL_LIGHTS_VERTEX _ADDITIONAL_LIGHTS
18.             #pragma multi_compile_fragment _ _SCREEN_SPACE_OCCLUSION
19.             #pragma multi_compile_fog
20.  
21.             #pragma vertex cs
22.             #pragma fragment fs
23.  
24.             #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
25.  
26.             struct Attributes
27.             {
28.                 float3 positionOS   : POSITION;
29.                 half3 normalOS      : NORMAL;
30.                 half4 tangentOS     : TANGENT;
31.                 float2 uv           : TEXCOORD0;
32.             };
33.  
34.             struct Varyings
35.             {
36.                 float4 positionWSAndFogFactor   : TEXCOORD1;
37.                 float4 positionCS               : SV_POSITION;
38.             };
39.  
40.             Varyings cs(Attributes input)
41.             {
42.                 VertexPositionInputs vertexInput = GetVertexPositionInputs(input.positionOS);
43.              
44.                 Varyings output;
45.                 output.positionCS = vertexInput.positionCS;
46.                 output.positionWSAndFogFactor = float4(vertexInput.positionWS, ComputeFogFactor(vertexInput.positionCS.z));
47.  
48.                 return output;
49.             }
50.  
51.             half4 fs(Varyings input) : SV_TARGET
52.             {
53.                 half3 col= MixFog(half3(1,1,1), input.positionWSAndFogFactor.w);
54.                 return half4(col,1);
55.             }
56.          
57.             ENDHLSL
58.         }
59.     }
60. }
61.  

And these shader keywords combos

Code (CSharp):

1.             #pragma multi_compile _ _MAIN_LIGHT_SHADOWS _MAIN_LIGHT_SHADOWS_CASCADE
2.             #pragma multi_compile _ _ADDITIONAL_LIGHTS_VERTEX _ADDITIONAL_LIGHTS
3.             #pragma multi_compile_fragment _ _SCREEN_SPACE_OCCLUSION
4.             #pragma multi_compile_fog

When I compile metal shader variants, no variants with both FOG_EXP2 and _SCREEN_SPACE_OCCLUSION set appear, i.e. they are stripped, even though they don't conflict.

If I remove

Code (CSharp):

1. #pragma multi_compile _ _MAIN_LIGHT_SHADOWS _MAIN_LIGHT_SHADOWS_CASCADE

or

Code (CSharp):

1. #pragma multi_compile _ _ADDITIONAL_LIGHTS_VERTEX _ADDITIONAL_LIGHTS

Doesn't matter which. Then recompiling the shader, FOG_EXP2 and SSAO appear in variant combinations that are compiled.

I'm guessing that this is a bug in the Shader Stripping logic, does anyone know if there tend to be issues with Unity incorrectly stripping valid combinations?

This hit me after upgrading and seeing missing shaders due to variants being stripped that are unexpected to be stripped.

(Note changing fog stripping settings in project -> graphics doesn't change the behaviour)

 

Hey, sorry I put it in the title but should've included it in the post!

2021.2.8

 

Via the unity shader compiler from the inspector and then checking the code output:

 

To demo the gif, I made a fresh urp project in 2021, copied the OP shader code into a new shader file, compiled the metal version, and inspected the compiled code.

Also just re-noting that this behaviour differs from 2020.3 where there are compiled variants mixing the two keywords.

 

Hit this exact issue this week. Not isolated to Metal, can confirm for D3D and GLES as well so I assume it doesn't matter which API.

 

Thanks for the update Juho! I can't follow that issue tracking link however?

 

Nice one! Out of curiosity will the fix land in the URP package, or is it a unity-core fix?

 

Oops, just found this after I submitted the bug report.

For what it's worth, it doesn't need some fancy keyword setup to replicate, I think just the existence of 3 more keywords triggers it.

It also has nothing to do with URP. (I'm using built-in)

In the submitted bug report I replicated it just by using the default unlit shader and:

Code (CSharp):

1.             #pragma multi_compile_fog
2.             #pragma multi_compile _ A_KEYWORD
3.             #pragma multi_compile _ OMG_A_KEYWORD
4.             #pragma multi_compile _ ANOTHER_KEYWORD

 

Is there any other work around for this besides removing all the multi compiles?

 

@Juho_Oravainen

There is also an issue with multi_compile_instancing in Unity versions 2021.2.8 and later. Procedural instancing shader variants are not included in builds. Will this also be fixed in 2021.2.12f1?

 

any date for that update?

 

Plz be smooth, strongly expect! If god exists plz make unity smooth!

 

I can only assume the process was not smooth?

 

sigh... definitely.

 

I forgot to say last month, but thank you for keeping us all updated @Juho-Oravainen

 

I am currently running into issues with Shaders being stripped in Windows Builds that shouldn't be.

Please check this thread: https://forum.unity.com/threads/released-lux-lit-particles.619897/page-2#post-8945316

This is in the latest 2021.3.22f1