using System;
using UnityEngine;
using UnityEngine.Rendering.PostProcessing;

[Serializable]
[PostProcess(typeof(DrawWorldSpacePositionRenderer), PostProcessEvent.AfterStack, "Custom/DrawWorldSpacePosition")]
public sealed class DrawWorldSpacePosition : PostProcessEffectSettings
{
}

public sealed class DrawWorldSpacePositionRenderer : PostProcessEffectRenderer<DrawWorldSpacePosition>
{
    public override void Render(PostProcessRenderContext context)
    {
        var sheet = context.propertySheets.Get(Shader.Find("Hidden/Custom/DrawWorldSpacePosition"));

        var camera = context.camera;

        var p = GL.GetGPUProjectionMatrix(camera.projectionMatrix, false);// Unity flips its 'Y' vector depending on if its in VR, Editor view or game view etc...
        p[2, 3] = p[3, 2] = 0.0f;
        p[3, 3] = 1.0f;
        var clipToWorld = Matrix4x4.Inverse(p * camera.worldToCameraMatrix) * Matrix4x4.TRS(new Vector3(0, 0, -p[2, 2]), Quaternion.identity, Vector3.one);
        sheet.properties.SetMatrix("clipToWorld", clipToWorld);

        context.command.BlitFullscreenTriangle(context.source, context.destination, sheet, 0);
    }
}

Shader "Hidden/Custom/DrawWorldSpacePosition"
{
    HLSLINCLUDE

        #include "../PostProcessing/Shaders/StdLib.hlsl"

        TEXTURE2D_SAMPLER2D(_CameraDepthTexture, sampler_CameraDepthTexture);

        uniform float4x4 clipToWorld;

        struct VaryingsExtended
        {
            float4 vertex : SV_POSITION;
            float2 texcoord : TEXCOORD0;
            float2 texcoordStereo : TEXCOORD1;
            float3 worldDirection : TEXCOORD2;
        };

        VaryingsExtended Vert(AttributesDefault v)
        {
            VaryingsExtended o;
            o.vertex = float4(v.vertex.xy, 0.0, 1.0);
            o.texcoord = TransformTriangleVertexToUV(v.vertex.xy);
        #if UNITY_UV_STARTS_AT_TOP
            o.texcoord = o.texcoord * float2(1.0, -1.0) + float2(0.0, 1.0);
        #endif

            o.texcoordStereo = TransformStereoScreenSpaceTex(o.texcoord, 1.0);
            o.worldDirection = mul(clipToWorld, o.vertext) - _WorldSpaceCameraPos;
            return o;
        }

        float4 Frag(VaryingsExtended i) : SV_Target
        {
            float depth = SAMPLE_DEPTH_TEXTURE(_CameraDepthTexture, sampler_CameraDepthTexture, i.texcoordStereo);
            depth = LinearEyeDepth(depth);
            float3 worldspace = i.worldDirection * depth + _WorldSpaceCameraPos;
            float4 color = float4(worldspace, 1.0);
            return color;
        } 

    ENDHLSL

    SubShader
    {
        Cull Off ZWrite Off ZTest Always

        Pass
        {
            HLSLPROGRAM 

                #pragma vertex Vert
                #pragma fragment Frag

            ENDHLSL
        }
    }
}