Question [SOLVED] URP: Screen effects for Single Pass VR (Sobel, Blur, ...)

Hey there,

I'm trying to get some shaders I wrote to work with Single Pass VR with URP. It works in Multi-Pass already and I'm happy with the result. I just can't make it work with Single Pass...

I guess the problem I'm having here is that I cannot sample the UV correctly, I've tried a couple of things but it just won't render in Single Pass on my Oculus Quest.

Code (CSharp):

1. Shader "Unlit/SobelFilter"
2. {
3.     Properties
4.     {
5.         _MainTex ("Base (RGB)", 2D) = "white" {}
6.     }
7.     SubShader
8.     {
9.         Tags { "RenderPipeline" = "UniversalPipeline" "RenderType"="Opaque" }
10.         LOD 200
11.        
12.         Pass
13.         {
14.             HLSLPROGRAM
15.             #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/SurfaceInput.hlsl"
16.             #include "Packages/com.unity.render-pipelines.core/ShaderLibrary/Color.hlsl"
17.              
18.             TEXTURE2D(_MainTex);
19.             SAMPLER(sampler_MainTex);
20.            
21.             CBUFFER_START(UnityPerMaterial)
22.             half4 _MainTex_ST;
23.             float2 _MainTex_TexelSize;
24.             CBUFFER_END;
25.            
26.             float _Intensity;
27.             float _Weight;
28.             float _Blend;
29.             half4 _OutlineColor;
30.             half4 _BackgroundColor;
31.             float _Threshold;
32.             float _SobelValue;
33.             float _ShowGrayscale;
34.            
35.             struct Attributes
36.             {
37.                 float4 positionOS       : POSITION;
38.                 float2 uv               : TEXCOORD0;
39.             };
40.  
41.             struct Varyings
42.             {
43.                 float2 uv        : TEXCOORD0;
44.                 float4 vertex : SV_POSITION;
45.                 UNITY_VERTEX_OUTPUT_STEREO
46.             };
47.            
48.             float2 UnityStereoScreenSpaceUVAdjust(float2 uv, float4 scaleAndOffset)
49.             {
50.                 return uv.xy * scaleAndOffset.xy + scaleAndOffset.zw;
51.             }
52.            
53.             float intensity(float4 color){
54.                 return sqrt((color.x*color.x)+(color.y*color.y)+(color.z*color.z));
55.             }
56.            
57.             float sobel(float stepx, float stepy, float2 uv)
58.             {
59.                 float tleft = intensity(SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv + float2(-stepx, stepy)));
60.                 float left = intensity(SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv + float2(-stepx, 0)));
61.                 float bleft = intensity(SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv + float2(-stepx, -stepy)));
62.                 float top = intensity(SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv + float2(0, stepy)));
63.                 float bottom = intensity(SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv + float2(0, -stepy)));
64.                 float tright = intensity(SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv + float2(stepx, stepy)));
65.                 float right = intensity(SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv + float2(stepx, 0)));
66.                 float bright = intensity(SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, uv + float2(stepx, -stepy)));
67.                
68.                 float x = (_SobelValue/2 * tleft) + (_SobelValue * left) + (_SobelValue/2 * bleft) - (_SobelValue/2 * tright) - (_SobelValue * right) - (_SobelValue/2 * bright);
69.                 float y = -(_SobelValue/2 * tleft) - (_SobelValue * top) - (_SobelValue/2 * tright) + (_SobelValue/2 * bleft) + (_SobelValue * bottom) + (_SobelValue/2 * bright);
70.                
71.                 float xlum = dot(x, float3(0.2126729, 0.7151522, 0.0721750));
72.                 float ylum = dot(y, float3(0.2126729, 0.7151522, 0.0721750));
73.                
74.                 float color = sqrt((xlum*xlum) + (ylum*ylum));
75.                
76.                 if(_ShowGrayscale == 1){
77.                     return color;
78.                 }
79.                
80.                 // Replacing all values bellow threshold to black and white above (greyscale to b&w)
81.                 if( color <= _Threshold ) { color = 0; }
82.                 else { color = 1; }
83.                
84.                 return color;
85.             }
86.            
87.             half4 applyColors(half4 s) {
88.                 // Replacing blacks with background color and whites with outline color
89.                 if (s.r == 0) {
90.                     s = _BackgroundColor;
91.                 } else if (s.r == 1) {
92.                     s = lerp(_BackgroundColor, _OutlineColor, _Intensity);
93.                 }
94.                 return s;
95.             }
96.            
97.             Varyings vert(Attributes input)
98.             {
99.                 Varyings output = (Varyings)0;
100.                 UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(output);
101.  
102.                 VertexPositionInputs vertexInput = GetVertexPositionInputs(input.positionOS.xyz);
103.                 output.vertex = vertexInput.positionCS;
104.                 output.uv = input.uv;
105.                
106.                 return output;
107.             }
108.             half4 frag (Varyings input) : SV_Target
109.             {
110.                 UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(input);
111.                
112.                 // Apply Sobel Filter
113.                 half4 s = sobel(_MainTex_TexelSize.x, _MainTex_TexelSize.y, UnityStereoScreenSpaceUVAdjust(input.uv, _MainTex_ST));
114.                 half4 color = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, UnityStereoScreenSpaceUVAdjust(input.uv, _MainTex_ST));
115.                
116.                 // Apply outline and background color
117.                 half4 r = applyColors(s);  
118.                
119.                 if(_ShowGrayscale == 1){
120.                     return s;
121.                 }
122.                    
123.                 // blending with normal texture and weight
124.                 r = lerp(r, r * color, _Blend);
125.                 r = lerp(color, r, _Weight);      
126.                 return r;
127.                    
128.             }
129.            
130.             #pragma vertex vert
131.             #pragma fragment frag
132.            
133.             ENDHLSL
134.         }
135.     }
136.     FallBack "Diffuse"
137. }
138.  

 

Solved : The solution is actually really straightforward and I think Unity should spend some time actually documenting the URP Shader macros a bit more, I found the solution on a forum post. There's nothing about it anywhere on the internet.

The trick is to use TEXTURE2D_X and SAMPLE_TEXTURE2D_X instead of TEXTURE2D and SAMPLE_TEXTURE2D. I also replaced my method

UnityStereoScreenSpaceUVAdjust(uv, _MainTex_ST) 

with

UnityStereoTransformScreenSpaceTex(uv).

These macros with the X as prefix are specifically designed for single pass VR

 

Can you offer some guidance on my blur shader?

I'm running in to the same issue with the Built in Renderer. The blur works in multi-pass but not in single-pass. I'm running a blur filter for each individual eye. When applied the left eye is gray and the right eye is black. Here's my shader code:

Code (CSharp):

1.  
2. Shader "Hidden/BlurEffectConeTap" {
3.     Properties { _MainTex ("", any) = "" {} }
4.     CGINCLUDE
5.     #include "UnityCG.cginc"
6.     struct v2f {
7.         float4 pos : SV_POSITION;
8.         half2 uv : TEXCOORD0;
9.         half2 taps[4] : TEXCOORD1;
10.     };
11.     sampler2D _MainTex;
12.     half4 _MainTex_TexelSize;
13.     half4 _MainTex_ST;
14.     half4 _BlurOffsets;
15.     v2f vert( appdata_img v ) {
16.         v2f o;
17.         o.pos = UnityObjectToClipPos(v.vertex);
18.  
19.         o.uv = v.texcoord - _BlurOffsets.xy * _MainTex_TexelSize.xy;
20. #ifdef UNITY_SINGLE_PASS_STEREO
21.         // we need to keep texel size correct after the uv adjustment.
22.         o.taps[0] = UnityStereoScreenSpaceUVAdjust(o.uv + _MainTex_TexelSize * _BlurOffsets.xy * (1.0f / _MainTex_ST.xy), _MainTex_ST), _MainTex_ST);
23.         o.taps[1] = UnityStereoScreenSpaceUVAdjust(o.uv - _MainTex_TexelSize * _BlurOffsets.xy * (1.0f / _MainTex_ST.xy), _MainTex_ST), _MainTex_ST);
24.         o.taps[2] = UnityStereoScreenSpaceUVAdjust(o.uv + _MainTex_TexelSize * _BlurOffsets.xy * half2(1, -1) * (1.0f / _MainTex_ST.xy), _MainTex_ST);
25.         o.taps[3] = UnityStereoScreenSpaceUVAdjust(o.uv - _MainTex_TexelSize * _BlurOffsets.xy * half2(1, -1) * (1.0f / _MainTex_ST.xy), _MainTex_ST);
26. #else
27.         o.taps[0] = o.uv + _MainTex_TexelSize * _BlurOffsets.xy;
28.         o.taps[1] = o.uv - _MainTex_TexelSize * _BlurOffsets.xy;
29.         o.taps[2] = o.uv + _MainTex_TexelSize * _BlurOffsets.xy * half2(1,-1);
30.         o.taps[3] = o.uv - _MainTex_TexelSize * _BlurOffsets.xy * half2(1,-1);
31. #endif
32.         return o;
33.     }
34.     half4 frag(v2f i) : SV_Target {
35.         half4 color = tex2D(_MainTex, i.taps[0]);
36.         color += tex2D(_MainTex, i.taps[1]);
37.         color += tex2D(_MainTex, i.taps[2]);
38.         color += tex2D(_MainTex, i.taps[3]);
39.         return color * 0.25;
40.     }
41.     ENDCG
42.     SubShader {
43.          Pass {
44.               ZTest Always Cull Off ZWrite Off
45.  
46.               CGPROGRAM
47.               #pragma vertex vert
48.               #pragma fragment frag
49.               ENDCG
50.           }
51.     }
52.     Fallback off
53. }
54.