Shader Screenspace Position Issue

I am trying to apply a post processing effect to all pixels outside of a certain range of my character.

This is the shader code I have so far for converting my players position into screenspace and testing each fragment against it.

Code (CSharp):

1. //Worldspace Player Pos
2. float4 _PlayerPosition;
3.  
4. float4 Frag(VaryingsDefault i) : SV_Target
5. {
6.     float4 playerPositionClipSpace = mul(unity_MatrixVP,_PlayerPosition);
7.     float3 playerPositionScreenSpace = playerPositionClipSpace.xyz / playerPositionClipSpace.w;
8.     playerPositionScreenSpace = playerPositionScreenSpace * 0.5 + 0.5;
9.  
10.     float4 color = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord);
11.     if (length(playerPositionScreenSpace.xy - i.texcoord) >= 0.1f)
12.     {
13.         color.rgb = float3(0,0,0);
14.     }
15.     return color;
16. }

My problem is, that the resulting circle is somehow not centered on the given character position.


Would appreciate if someone has an idea for why that may be the case

 

Okay I figured it out on my own. The issue was that when running on DirectX Texture Coordinates need to be flipped on the y-axis.
https://docs.unity3d.com/Manual/SL-PlatformDifferences.html has more information

This is how I did it in case anyone else runs into this issue and is confused.

Code (CSharp):

1.  if (length(playerPositionNDC - float2(i.texcoord.x,1-i.texcoord.y)) >= 0.1f)

The result is now correctly centered on the playerPosition.