dolphin/Data/User/Shaders/invertedoutline.txt

uniform samplerRECT samp0 : register(s0);

void main(out float4 ocol0 : COLOR0, in float2 uv0 : TEXCOORD0)
{
  float4 c0 = texRECT(samp0, uv0).rgba;
  float4 c1 = texRECT(samp0, uv0 + float2(5,5)).rgba;

  ocol0 = c0 - c1;
}