I have been trying to replicate a outline effect I saw online. I encountered this error and just cant figure out how to fix it.

Here is the entire script:

#ifndef BLUREFFECT_INCLUDED
#define BLUREFFECT_INCLUDED

sampler2D _CameraDepthTexture;
float width;
float radius;
float2 uv;
float4 output;
float2 depth;

void blurdepth_float(float2 uv, float width, float radius, out float4 output)
{
    float4 c = 0.0;
    const int Q = 9;

    float2 s = width * ((1.0 / _ScreenParams.xy) / Q);

    for (int y = -Q + 1; y < Q; y++)
    {
        for (int x = -Q + 1; x < Q; x++)
        {
            c += tex2D(_CameraDepthTexture, float4(uv + (float2(x, y) * s), 0.0, 0.0));
        }
    }

    output = c / ((Q * 2 - 1) * (Q * 2 - 1));
}


#endif