Resolved How to get the instance ID while using custom SRP?

That's probably a stupid question, but how can I get the instance ID when I render meshes using Graphics.RenderMeshPrimitives while using custom SRP? Documentation (https://docs.unity3d.com/Manual/gpu-instancing-shader.html) says that I should declare a structure with UNITY_VERTEX_INPUT_INSTANCE_ID, pass it in my shader function and there I can get instance ID by vertexInput.instanceID if there was #ifdef INSTANCING_ON.

But I get invalid subscript 'instanceID' compile error. Here's the minimal code illustrating the situation.

Code (CSharp):

1. StructuredBuffer<float4x4> _Matrices;
2.  
3. struct Varyings
4. {
5.   float4 positionCS : SV_POSITION;
6.   UNITY_VERTEX_INPUT_INSTANCE_ID
7. };
8.  
9. Varyings UnlitPassVertex(Attributes input)
10. {
11.   Varyings output;
12.   UNITY_SETUP_INSTANCE_ID(input);
13.   #ifdef INSTANCING_ON
14.   float4x4 m = _Matrices[input.instanceID];
15.   #else
16.   float4x4 m = 1.0;
17.   #endif
18.   float4 w = mul(m, float4(input.positionOS, 1.0));
19.   float4 c = mul(unity_MatrixVP, w);
20.   output.positionCS = c;
21.   return output;
22. }

The fact that to get the error I must write manually #define INSTANCING_ON makes me think that I'm doing something wrong. Despite that problem instancing workd just fine. Pipeline is duplicating one from Catlike Coding tutorial (https://catlikecoding.com/unity/tutorials/custom-srp/draw-calls/).

 

Have you included required files to your shader? Not familiar with SRP, but generally you would need to include "UnityInstancing.cginc"

Also, UNITY_VERTEX_INPUT_INSTANCE_ID basically just unfolds to `uint instanceID : SV_InstanceID`.

 

I think so. Cause all other stuff like UNITY_VERTEX_INPUT_INSTANCE_ID, UNITY_SETUP_INSTANCE_ID, UNITY_ACCESS_INSTANCED_PROP is working as expected. I used

#include "Packages/com.unity.render-pipelines.core/ShaderLibrary/UnityInstancing.hlsl"

though, according to that tutorial.

Great! Such replacement gave the correct behavior. But apparently in my case UNITY_VERTEX_INPUT_INSTANCE_ID unfolds to something else. I tried to read UnityInstancing.hlsl, but didn't succeed.

 

Moreover, even such thing compiles:

struct Attributes

{

   float3 positionOS : POSITION;

   UNITY_VERTEX_INPUT_INSTANCE_ID

   uint instanceID : SV_InstanceID;

};

 

I don't think it can unfold to anything else, see source code for SRP: https://github.com/needle-mirror/co...master/ShaderLibrary/UnityInstancing.hlsl#L83
It only compiles to something else if SHADER_API_PSSL is defined and I have no idea what that is

This can only happen if you include UnityInstancing.hlsl after defining your struct or if you didn't add instancing multi_compile

 

You're absolutely right. I was confused with some bug in Unity, I think.

When I use UNITY_VERTEX_INPUT_INSTANCE_ID in my vertex attributes, and then access instance ID by input.instanceID I get the error message invalid subscript 'instanceID'. But when I hit Play it disappears and everything work fine.

Unity version used is 2022.3.5f1. 2023.1.6f1 -- the same.