Unexpected behaviour when sampling reflection probe in URP shader

Unity Engine
, ,
1

When writing custom URP shader I stumbled onto a problem with sampling reflection probe using SAMPLE_TEXTURECUBE_LOD() macro. Function flattens the mesh along local X-axis when shader is compatible with SRP Batcher:

1186Ă—677 120 KB

Function works as intended if when SRP batching is incompatible:
1190Ă—676 127 KB

Here is the shader I used for testing, I remove CBUFFER_START and CBUFFER_END lines to break to SRP Batcher compatibility.

Shader "Unlit/sh_urp_template"
{
    Properties
    {
        _test ("test", Float) = 1
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" "LightMode" = "UniversalForward"}
        LOD 100

        Pass
        {
            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

            struct appdata
            {
                float4 vertex : POSITION;
                float3 normal : NORMAL;
            };

            struct v2f
            {
                float3 normal : NORMAL;
                float4 vertex : SV_POSITION;
            };

            CBUFFER_START(UnityPerMaterial)
            float _test;
            CBUFFER_END

            v2f vert (appdata v)
            {
                v2f o;
                o.normal = mul( UNITY_MATRIX_M, float4( v.normal, 0.0 ) ).xyz;
                o.vertex = TransformObjectToHClip(v.vertex.xyz);
                return o;
            }

            half4 frag (v2f i) : SV_Target
            {
                half4 refl = SAMPLE_TEXTURECUBE_LOD(unity_SpecCube0,samplerunity_SpecCube0, i.normal, 0);
                return refl*_test;
            }
            ENDHLSL
        }
    }
}
1 Like
2

I am experiencing this as well, in particular I have been following CatlikeCoding’s Custom SRP Tutorials it does seem to be caused due to SRP Batching

batching
batching1532Ă—702 160 KB

GPU Instancing does not have the same issue and works fine

Unity Version: 2022.3.11f1
Core RP Library: 14.0.9

3

Where you use
o.normal = mul( UNITY_MATRIX_M, float4( v.normal, 0.0 ) ).xyz;

It ought to be:
o.normal = TransformObjectToWorldNormal(v.normal).xyz;

Unity the UNITY_MATRIX_M matrix (and the likes) directly is not in line with SRP shader code best practices. Adopting the function may just resolve the issue right away!

The function unrolls to:
image

4

it still looks wrong with TransformObjectToWorldNormal():
image