downsampled depth pass for the volumetric light tutorial

VolumetricLightTutoDepth.shader

Pass
{
    Name "SampleDepth"

    HLSLPROGRAM
    #pragma vertex vert
    #pragma fragment frag
    #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/DeclareDepthTexture.hlsl"
    #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Lighting.hlsl"

    struct appdata
    {
        real4 vertex : POSITION;
        real2 uv : TEXCOORD0;
    };

    struct v2f
    {
        real2 uv : TEXCOORD0;
        real4 vertex : SV_POSITION;
    };

    v2f vert (appdata v)
    {
        v2f o;
        o.vertex = TransformWorldToHClip(v.vertex);
        o.uv = v.uv;
        return o;
    }

    real frag (v2f i) : SV_Target
    {
        #if UNITY_REVERSED_Z
            real depth = SampleSceneDepth(i.uv);
        #else
            // Adjust z to match NDC for OpenGL
            real depth = lerp(UNITY_NEAR_CLIP_VALUE, 1, SampleSceneDepth(i.uv));
        #endif
        return depth;
    }
    ENDHLSL
}