/*
 * Copyright (c) Contributors to the Open 3D Engine Project.
 * For complete copyright and license terms please see the LICENSE at the root of this distribution.
 *
 * SPDX-License-Identifier: Apache-2.0 OR MIT
 *
 */

#include <scenesrg.srgi>
#include <viewsrg.srgi>

#include <Atom/Features/PostProcessing/FullscreenVertexUtil.azsli>
#include <Atom/Features/PostProcessing/FullscreenPixelInfo.azsli>
#include <Atom/Features/MatrixUtility.azsli>
#include <Atom/Features/PBR/LightingUtils.azsli>
#include <Atom/Features/PBR/Microfacet/Fresnel.azsli>

ShaderResourceGroup PassSrg : SRG_PerPass
{
    Texture2DMS<float>  m_depth;
    Texture2DMS<float4> m_normal;       // RGB10 = Normal (Encoded), A2 = Flags
    Texture2DMS<float4> m_specularF0;   // RGB8 = SpecularF0, A8 = Roughness
}

#include <Atom/RPI/ShaderResourceGroups/DefaultDrawSrg.azsli>
#include "ReflectionCommon.azsli"
#include "ReflectionScreenSpaceTrace.azsli"

struct VSInput
{
    uint m_vertexID : SV_VertexID;
};

struct VSOutput
{
    float4 m_position : SV_Position;
    float2 m_texCoord : TEXCOORD0;
};

// Vertex Shader
VSOutput MainVS(VSInput input)
{
    VSOutput OUT;

    float4 posTex = GetVertexPositionAndTexCoords(input.m_vertexID);
    OUT.m_texCoord = float2(posTex.z, posTex.w);
    OUT.m_position = float4(posTex.x, posTex.y, 0.0, 1.0);
    return OUT;
}

// Pixel Shader
PSOutput MainPS(VSOutput IN)
{
    // compute screen coords based on a half-res render target
    float2 screenCoords = IN.m_position.xy * 2.0f;
       
    uint2 dimensions;
    uint samples;
    PassSrg::m_depth.GetDimensions(dimensions.x, dimensions.y, samples);
    float2 UV = saturate(screenCoords / dimensions.xy);

    float depth = PassSrg::m_depth.Load(screenCoords, 0).r;
    if (depth == 0.0f)
    {
        // skip tracing rays at max scene depth
        discard;
    }
        
    // compute view space surface position
    float2 ndcPos = float2(UV.x, 1.0f - UV.y) * 2.0f - 1.0f;
    float4 projectedPos = float4(ndcPos, depth, 1.0f);
    float4 positionVS = mul(ViewSrg::m_projectionMatrixInverse, projectedPos);
    positionVS /= positionVS.w;

    // normalize the viewspace position to get the camera-to-position vector
    float3 cameraToPositionVS = normalize(positionVS);  

    // retrieve surface normal
    float4 encodedNormal = PassSrg::m_normal.Load(screenCoords, 0);
    float3 normalWS = DecodeNormalSignedOctahedron(encodedNormal.rgb);
    float3 normalVS = normalize(mul(ViewSrg::m_viewMatrix, float4(normalWS, 0.0f)).xyz);

    // reflect view ray around surface normal
    float3 reflectDirVS = normalize(reflect(cameraToPositionVS, normalVS));
 
    // trace screenspace rays against the depth buffer to find the screenspace intersection coordinates    
    float4 result = float4(0.0f, 0.0f, 0.0f, 0.0f);
    float2 hitCoords = float2(0.0f, 0.0f);
    if (TraceRayScreenSpace(positionVS, reflectDirVS, dimensions, hitCoords))
    {
        float rdotv = dot(reflectDirVS, cameraToPositionVS);
        result = float4(hitCoords, 0.0f, rdotv);   
    }

    PSOutput OUT;
    OUT.m_color = result;
    return OUT;
}