Matrix4x4 v = renderingData.cameraData.GetViewMatrix();
Matrix4x4 p = renderingData.cameraData.GetProjectionMatrix();
v.SetColumn(3, new Vector4(0, 0, 0, 1));
Matrix4x4 vpInv = (p * v).inverse;

Vector3 topLeftCorner = vpInv.MultiplyPoint(new Vector3(-1, -1, -1));
Vector3 topRightCorner = vpInv.MultiplyPoint(new Vector3(1, -1, -1));
Vector3 bottomLeftCorner = vpInv.MultiplyPoint(new Vector3(-1, 1, -1));

_ssrMat.SetVector(CamPosToNearLeftUpperVec, topLeftCorner);
_ssrMat.SetVector(NearTopLeftToTopRightVec, topRightCorner - topLeftCorner);
_ssrMat.SetVector(NearTopLeftToBottomLeftVec,   bottomLeftCorner - topLeftCorner);


Pass
{
    HLSLPROGRAM
    #pragma vertex Vert
    #pragma fragment frag
    #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
    #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/DeclareDepthTexture.hlsl"
    #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/DeclareNormalsTexture.hlsl"
    #include "Packages/com.unity.render-pipelines.core/Runtime/Utilities/Blit.hlsl"

    CBUFFER_START(UnityPerMaterial)
        int _MaxMarchStep;
        float _MarchStepLength;
        float _MarchThreshold;
        float3 _CamPosToNearLeftUpperVec;
        float3 _NearTopLeftToTopRightVec;
        float3 _NearTopLeftToBottomLeftVec;
    CBUFFER_END

    float3 ReconstructPositionWSRelativeToCamera(float2 uv)
    {
        float depth = LinearEyeDepth(SampleSceneDepth(uv), _ZBufferParams);
        float3 positionWSIntersectWithNear =
            _CamPosToNearLeftUpperVec
            + uv.x * _NearTopLeftToTopRightVec
            + uv.y * _NearTopLeftToBottomLeftVec;
        // scalene triangle
        return depth / _ProjectionParams.y * positionWSIntersectWithNear;
    }

    void ReconstructUVAndDepth(float3 positionWS, out float2 uv, out float depth)
    {
        float4 positionCS = TransformWorldToHClip(positionWS);
        uv = float2(positionCS.x, positionCS.y * _ProjectionParams.x) / positionCS.w * 0.5 + 0.5;
        depth = positionCS.w;
    }

    float3 frag(Varyings IN) : SV_Target
    {
        float3 positionWSSurfaceRel = ReconstructPositionWSRelativeToCamera(IN.texcoord);
        float3 reflectDirWS = normalize(reflect(normalize(positionWSSurfaceRel), SampleSceneNormals(IN.texcoord)));
        UNITY_LOOP
        for (int step = 0; step < _MaxMarchStep; ++step)
        {
            float3 positionWSRel = positionWSSurfaceRel + step * _MarchStepLength * reflectDirWS;
            float2 uv;
            float rayDepth;
            ReconstructUVAndDepth(positionWSRel + _WorldSpaceCameraPos, uv, rayDepth);
            float surfaceDepth = LinearEyeDepth(SampleSceneDepth(uv), _ZBufferParams);
            if (rayDepth > surfaceDepth && rayDepth < surfaceDepth + _MarchThreshold)
                return SAMPLE_TEXTURE2D(_BlitTexture, sampler_LinearRepeat, uv);
                // return abs(positionWSRel + _WorldSpaceCameraPos);
        }
        // return abs(positionWSSurfaceRel + _WorldSpaceCameraPos);
        return SAMPLE_TEXTURE2D(_BlitTexture, sampler_LinearRepeat, IN.texcoord);
    }
    ENDHLSL
}