Question 3D Pixelization Shader with 1 pixel Outline

I am trying to pixelize a 3d scene using a urp full screen shader. It does work and i even got an outline working but i would like for the outline to be 1 pixel wide, which it currently isn't. Where is the Problem?

Code (CSharp):

1. Shader "Pixel"
2. {
3.         SubShader
4.     {
5.         Tags { "RenderType"="Opaque" "RenderPipeline" = "UniversalPipeline"}
6.         LOD 100
7.         ZWrite Off Cull Off
8.         Pass
9.         {
10.             Name "PixelPass"
11.  
12.             HLSLPROGRAM
13.             #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
14.             // The Blit.hlsl file provides the vertex shader (Vert),
15.             // input structure (Attributes) and output strucutre (Varyings)
16.             #include "Packages/com.unity.render-pipelines.core/Runtime/Utilities/Blit.hlsl"
17.  
18.             #pragma vertex Vert
19.             #pragma fragment frag
20.  
21.             TEXTURE2D_X(_CameraOpaqueTexture);
22.             SAMPLER(sampler_CameraOpaqueTexture);
23.  
24.             //depth texture
25.             TEXTURE2D_X(_CameraDepthTexture);
26.             SAMPLER(sampler_CameraDepthTexture);
27.  
28.             int _ScreenSizeX;
29.             int _ScreenSizeY;
30.             float4 _OutlineColor;
31.             float _OutlineThreshold;
32.  
33.             half4 frag (Varyings input) : SV_Target
34.             {
35.                 UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(input);
36.                 //pixelate screen to fit the screen size with point sampling
37.                 float2 uv = input.texcoord.xy;
38.                 float2 pixelSize = float2(1.0f / _ScreenSizeX, 1.0f / _ScreenSizeY);
39.                 float2 pixelCenter = floor(uv / pixelSize) * pixelSize + pixelSize * 0.5f;
40.                 //apply outline color if the one around different depth
41.                 float depth = SAMPLE_TEXTURE2D_X(_CameraDepthTexture,sampler_CameraDepthTexture, pixelCenter.xy);
42.                 //check one pixel above, below, left, right and if the depth is different, apply outline color
43.                 float depthAbove = SAMPLE_TEXTURE2D_X(_CameraDepthTexture,sampler_CameraDepthTexture, pixelCenter.xy + float2(0.0f, pixelSize.y));
44.                 float depthBelow = SAMPLE_TEXTURE2D_X(_CameraDepthTexture,sampler_CameraDepthTexture, pixelCenter.xy - float2(0.0f, pixelSize.y));
45.                 float depthLeft = SAMPLE_TEXTURE2D_X(_CameraDepthTexture,sampler_CameraDepthTexture, pixelCenter.xy - float2(pixelSize.x, 0.0f));
46.                 float depthRight = SAMPLE_TEXTURE2D_X(_CameraDepthTexture,sampler_CameraDepthTexture, pixelCenter.xy + float2(pixelSize.x, 0.0f));
47.                 float depthDiff = abs(depth - depthAbove) + abs(depth - depthBelow) + abs(depth - depthLeft) + abs(depth - depthRight);
48.                 float4 color = float4(0.0f, 0.0f, 0.0f, 1.0f);
49.                 if (depthDiff > _OutlineThreshold)
50.                 {
51.                     color = _OutlineColor;
52.                 }
53.                 else
54.                 {
55.                     color = SAMPLE_TEXTURE2D_X(_CameraOpaqueTexture, sampler_CameraOpaqueTexture, pixelCenter);
56.                 }
57.  
58.  
59.                 return color;
60.  
61.             }
62.             ENDHLSL
63.         }
64.     }
65. }

 

Figured out i can always devide pixelSize with 2. Still not perfect though

 

You're using abs for the difference. This means that it doesnt care if the compared depths are either behind or front, ending up with two pixel wide outlines.