Question Issues with DrawProcedural / RenderPrimitives in 2022.3

I'm trying to upgrade a project from 2021.3.22 to 2022.3.8. This project has a procedural instancing surface shader called with DrawProcedural. But it doesn't appear to work in 2022.3.8. It is either drawing only 1 instance - or always returning 0 as the instanceID in the shader.

I thought it might be because DrawProcedural is obsolete in 2022.3.8 so I converted the code to RenderPrimitives, but it suffers the same issue.

To diagnose, I took the example code from RenderPrimitives and converted the shader to a surface shader. This has the same problem in that it works in version 2021.3 but doesn't work in 2022.3. (One note is that I have to manually add the PROCEDURAL_INSTANCING_ON keyword to the material to get it to do anything on either version - is this an indication that I'm missing something from the shader?)

Example procedural instancing surface shader below. Can you let me know if you think it should work - or should I report it as a bug?

Code (ShaderLab):

1. Shader "ProceduralSurface"
2. {
3.     Properties
4.     {
5.         _Color ("Color", Color) = (1,1,1,1)
6.         _MainTex ("Albedo (RGB)", 2D) = "white" {}
7.         _Glossiness ("Smoothness", Range(0,1)) = 0.5
8.         _Metallic ("Metallic", Range(0,1)) = 0.0
9.     }
10.     SubShader
11.     {
12.         Tags { "RenderType"="Opaque" }
13.         LOD 200
14.  
15.         CGPROGRAM
16.         #include "UnityInstancing.cginc"
17.         // Physically based Standard lighting model, and enable shadows on all light types
18.         #pragma surface surf Standard fullforwardshadows vertex:vert finalcolor:mycolor
19.         #pragma instancing_options procedural:setup
20.  
21.         // Use shader model 3.0 target, to get nicer looking lighting
22.         #pragma target 3.0
23.  
24.         sampler2D _MainTex;
25.  
26.         struct appdata
27.         {
28.             float4 vertex : POSITION;
29.             float3 normal : NORMAL;
30.             float4 texcoord : TEXCOORD0;
31.             float4 texcoord1 : TEXCOORD1;
32.             float4 texcoord2 : TEXCOORD2;
33.             float4 tangent : TANGENT;
34.             fixed4 color : COLOR;
35.             uint vertexID : SV_VertexID;
36.             UNITY_VERTEX_INPUT_INSTANCE_ID
37.         };
38.        
39.         struct Input
40.         {
41.             float2 uv_MainTex;
42.             fixed4 color;
43.         };
44.  
45.         half _Glossiness;
46.         half _Metallic;
47.         fixed4 _Color;
48. #if defined (SHADER_API_D3D11)
49.         StructuredBuffer<int> _Triangles;
50.         StructuredBuffer<float3> _Positions;
51. #endif
52.         uniform uint _StartIndex;
53.         uniform uint _BaseVertexIndex;
54.         uniform float4x4 _ObjectToWorld;
55.         uniform float _NumInstances;
56.  
57.         //// Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
58.         //// See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
59.         //// #pragma instancing_options assumeuniformscaling
60.         UNITY_INSTANCING_BUFFER_START(Props)
61.             // put more per-instance properties here
62.         UNITY_INSTANCING_BUFFER_END(Props)
63.  
64.         void setup() {}
65.  
66.         void vert(inout appdata v, out Input d)
67.         {
68.             UNITY_INITIALIZE_OUTPUT(Input, d);
69.             UNITY_SETUP_INSTANCE_ID(v);
70. #if defined(UNITY_PROCEDURAL_INSTANCING_ENABLED)
71.             uint vertexID = v.vertexID;
72.             uint instanceID = UNITY_GET_INSTANCE_ID(v);
73.             float3 pos = _Positions[_Triangles[vertexID + _StartIndex] + _BaseVertexIndex];
74.             float4 wpos = mul(_ObjectToWorld, float4(pos + float3(instanceID, 0, 0), 1.0f));
75.             v.vertex = wpos;
76.             d.color = fixed4(instanceID / _NumInstances, 0, 0, 1);
77. #endif
78.         }
79.  
80.         void mycolor(Input IN, SurfaceOutputStandard o, inout fixed4 color)
81.         {
82.             color.rgb = IN.color;
83.         }
84.  
85.         void surf (Input IN, inout SurfaceOutputStandard o)
86.         {
87.             fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
88.             o.Albedo = c.rgb;
89.             // Metallic and smoothness come from slider variables
90.             o.Metallic = _Metallic;
91.             o.Smoothness = _Glossiness;
92.             o.Alpha = c.a;
93.         }
94.         ENDCG
95.     }
96.     FallBack "Diffuse"
97. }

 

I've also noticed that I'm getting different results with DrawProcedural and RenderPrimitives, are the instanceCount limits different for these calls?

 

We've tracked this down to a specific Unity revision. It's working in 2021.3.29 and broken in 2021.3.30.

 

IN-54270

Thanks.

 

It turns out the reason I was seeing a difference was because of the culling mode.