unity_InstanceID always 0 in URP?

I'm probably doing something wrong, but I'm using the
DrawMeshInstancedIndirect with MonoBehaviour example verbatim from the docs:
https://docs.unity3d.com/ScriptReference/Graphics.DrawMeshInstancedIndirect.html
with this shader:

Code (CSharp):

1. Shader "Unlit/InstancedTest"
2. {
3.     SubShader
4.     {
5.         Tags { "RenderType"="Opaque" }
6.         LOD 100
7.  
8.         Pass
9.         {
10.             CGPROGRAM
11.             #pragma vertex vert
12.             #pragma fragment frag
13.             #pragma multi_compile_instancing
14.             #pragma instancing_options procedural:setup
15.             #pragma target 4.5
16.  
17.             #include "UnityCG.cginc"
18.  
19.             struct appdata
20.             {
21.                 float4 vertex : POSITION;
22.                 UNITY_VERTEX_INPUT_INSTANCE_ID
23.             };
24.  
25.             struct v2f
26.             {
27.                 float4 vertex : SV_POSITION;
28.                 fixed4 color : COLOR;          
29.             };
30.  
31.             v2f vert (appdata v)
32.             {
33.                 v2f o;
34.                 o.vertex = v.vertex;
35.                 o.color = fixed4(0,1,0,1);;
36.  
37. #if defined(UNITY_PROCEDURAL_INSTANCING_ENABLED)
38.                 o.vertex += float4(-unity_InstanceID.xxx, 0);
39.                 o.color = fixed4(1,0,unity_InstanceID*0.25,1);
40. #endif
41.                 o.vertex = UnityObjectToClipPos(o.vertex);
42.                 return o;
43.             }
44.  
45.             fixed4 frag (v2f i) : SV_Target
46.             {
47.                 fixed4 col = i.color;
48.                 return col;
49.             }
50.             ENDCG
51.         }
52.     }
53. }

What I would expect to see is my instanced mesh ( a sphere) offset in space and color for each instance. Instead, all I see is 1 red sphere. It's red, which means that
UNITY_PROCEDURAL_INSTANCING_ENABLED is defined, otherwise it would be green. I'm guessing
- all the instances have id 0 are drawing on top of each other
- or there is only one instance being drawn.
Any thoughts on what I'm missing or if this won't work in URP?

edit:
since UNITY_VERTEX_INPUT_INSTANCE_ID I also tried this, but same result, single red mesh

#if defined(UNITY_PROCEDURAL_INSTANCING_ENABLED)

                o.vertex += float4(-v.instanceID.xxx, 0);

                o.color = fixed4(1,0,v.instanceID*0.25,1);

#endif

 

I've been able to reproduce in Classic renderer as well. However, using explicit SV_InstanceID does work for Classic and URP.

Code (CSharp):

1. Shader "Unlit/InstancedTest"
2. {
3.     SubShader
4.     {
5.         Tags { "RenderType"="Opaque" }
6.         LOD 100
7.  
8.         Pass
9.         {
10.             CGPROGRAM
11.             #pragma vertex vert
12.             #pragma fragment frag
13.  
14.             struct appdata
15.             {
16.                 float4 vertex : POSITION;
17.                 uint instanceID : SV_InstanceID;
18.             };
19.  
20.             struct v2f
21.             {
22.                 float4 vertex : SV_POSITION;
23.                 fixed4 color : COLOR;        
24.             };
25.  
26.             v2f vert (appdata v)
27.             {
28.                 float3 worldPosition = v.vertex.xyz + float4(v.instanceID.xxx, 0);
29.                 fixed4 color =  fixed4(1,0,v.instanceID*0.01,1);
30.  
31.                 v2f o;
32.                 o.vertex = mul(UNITY_MATRIX_VP, float4(worldPosition, 1.0f));
33.                 o.color = color;
34.                 return o;
35.             }
36.  
37.             fixed4 frag (v2f i) : SV_Target
38.             {
39.                 fixed4 col = i.color;
40.                 return col;
41.             }
42.             ENDCG
43.         }
44.     }
45. }

 

Wow, I've been trying to find a solution for this problem for hours. This is the one post I found that actually gets me access to the instance ID and all I had to do was include it in the appdata struct ... crazy ...

 

Hi! This remains broken. The docs occasionally mention the existence of unity_InstanceID but never show how it's used. Can this be fixed, or the docs improved?