Creating Image effects for SinglePass stereo rendering with multiple shader passes.

I am creating a simple bloom effect for a Oculus quest app. It works in multi pass rendering but am having some issues making it work in single pass stereo rendering. I was following this docs: https://docs.unity3d.com/Manual/Android-SinglePassStereoRendering.html
and for simplicity have made a simple image effect that demonstrates the problem i have. It has 2 shader passes. The first one just inverts the colors and the second one creates a grayscale from the red channel. Both passes work by themselves and work together in multipass rendering but in single pass i get a grayish white left eye and a black right eye.
Here is the shader

Code (CSharp):

1. Shader "Hidden/InvertColours"
2. {
3.     Properties
4.     {
5.         _MainTex ("Texture", 2D) = "white" {}
6.     }
7.  
8.     CGINCLUDE
9.     #include "UnityCG.cginc"
10.  
11.     UNITY_DECLARE_SCREENSPACE_TEXTURE(_MainTex);
12.     uniform    half4 _MainTex_ST;
13.  
14.     struct appdata
15.     {
16.         float4 vertex : POSITION;
17.         float2 uv : TEXCOORD0;
18.     };
19.  
20.     struct v2f
21.     {
22.         float2 uv : TEXCOORD0;
23.         float4 vertex : SV_POSITION;
24.         UNITY_VERTEX_OUTPUT_STEREO
25.     };
26.  
27.     v2f vertPass1 (appdata v)
28.     {
29.         v2f o;
30.         UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o)
31.         o.vertex = UnityObjectToClipPos(v.vertex);
32.         o.uv = TRANSFORM_TEX(v.uv, _MainTex);
33.         return o;
34.     }
35.  
36.     fixed4 fragPass1 (v2f i) : SV_Target
37.     {
38.         UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(i);
39.         fixed4 col = UNITY_SAMPLE_SCREENSPACE_TEXTURE(_MainTex, i.uv);
40.         // just invert the colors
41.         col.rgb = 1 - col.rgb;
42.         return col;
43.     }
44.  
45.      v2f vertPass2 (appdata v)
46.     {
47.         v2f o;
48.         UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o)
49.         o.vertex = UnityObjectToClipPos(v.vertex);
50.         o.uv = TRANSFORM_TEX(v.uv, _MainTex);
51.         return o;
52.     }
53.  
54.     fixed4 fragPass2 (v2f i) : SV_Target
55.     {
56.         UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(i);
57.         fixed4 col = UNITY_SAMPLE_SCREENSPACE_TEXTURE(_MainTex, i.uv);
58.         // just make a greyscale from red chanel
59.         col.rgb = col.rrr;
60.         return col;
61.     }
62.     ENDCG
63.  
64.     SubShader
65.     {
66.         // No culling or depth
67.         Cull Off ZWrite Off ZTest Always
68.  
69.         Pass
70.         {
71.             CGPROGRAM
72.             #pragma vertex vertPass1
73.             #pragma fragment fragPass1
74.  
75.             ENDCG
76.         }
77.  
78.         Pass
79.         {
80.             CGPROGRAM
81.             #pragma vertex vertPass2
82.             #pragma fragment fragPass2
83.  
84.             ENDCG
85.         }
86.     }
87. }
88.  

and here is the cs script attached to the camera:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. [ExecuteInEditMode]
6. [RequireComponent(typeof(Camera))]
7. public class InvertColours : MonoBehaviour
8. {
9.     public Material fastInvertColourMaterial = null;
10.  
11.     private void OnRenderImage(RenderTexture source, RenderTexture destination)
12.     {
13.         RenderTexture rt = RenderTexture.GetTemporary(source.width, source.height, 0, source.format);
14.         Graphics.Blit(source, rt, fastInvertColourMaterial, 0);
15.         Graphics.Blit(rt, destination, fastInvertColourMaterial, 1);
16.     }
17.  
18. }
19.  

 

Here is the solution for anyone wondering. The RenderTexture needs to be set up correctly to store data between passes. Hope it helps.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.XR;
5.  
6. [ExecuteInEditMode]
7. [RequireComponent(typeof(Camera))]
8. public class InvertColours : MonoBehaviour
9. {
10.     public Material fastInvertColourMaterial = null;
11.  
12.     private void OnRenderImage(RenderTexture source, RenderTexture destination)
13.     {
14.         RenderTextureDescriptor desc;
15.         if (XRSettings.enabled)
16.             desc = XRSettings.eyeTextureDesc;
17.         else
18.             desc = new RenderTextureDescriptor(Screen.width, Screen.height); // Not XR
19.  
20.         RenderTexture rt = RenderTexture.GetTemporary(desc);
21.         Graphics.Blit(source, rt, fastInvertColourMaterial, 0);
22.         Graphics.Blit(rt, destination, fastInvertColourMaterial, 1);
23.         RenderTexture.ReleaseTemporary(rt);
24.     }
25.  
26. }

 

Thanks for this information, seems one of the most vital parts is missing in stereo documentation.

I wonder if this is same handling if use a quad to draw directly to screen with GL functions ?