/*
 * 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 <Atom/Features/SrgSemantics.azsli>

#include <Atom/Features/PostProcessing/FullscreenPixelInfo.azsli>
#include <Atom/Features/PostProcessing/FullscreenVertex.azsli>
#include <Atom/Features/PostProcessing/PostProcessUtil.azsli>

ShaderResourceGroup PassSrg : SRG_PerPass
{
    Texture2D<float4> m_diffuseFrameBuffer;
    Texture2D<float4> m_specularFrameBuffer;
    
    Sampler LinearSampler
    {
        MinFilter = Linear;
        MagFilter = Linear;
        MipFilter = Linear;
        AddressU = Clamp;
        AddressV = Clamp;
        AddressW = Clamp;
    };
}

PSOutput MainPS(VSOutput IN)
{
    PSOutput OUT;

    // 2x2 box filter to reduce noises introduced by undersampled subsurface scattering
    
    float4 diffuse = PassSrg::m_diffuseFrameBuffer.Sample(PassSrg::LinearSampler, IN.m_texCoord);
    if(diffuse.w > 0.0)
    {
        // Center pixel always valid
        float3 sum = 0.25 * diffuse.rgb;
        float weightSum = 0.25;
        
        float3 color;
        float weight;
        
        // Up
        color = PassSrg::m_diffuseFrameBuffer.Sample(PassSrg::LinearSampler, IN.m_texCoord, int2(0, -1)).rgb;
        weight = color.x + color.y + color.z > 0.0 ? 0.25 : 0.0;
        sum += weight * color;
        weightSum += weight;
            
        // Left
        color = PassSrg::m_diffuseFrameBuffer.Sample(PassSrg::LinearSampler, IN.m_texCoord, int2(-1, 0)).rgb;
        weight = color.x + color.y + color.z > 0.0 ? 0.25 : 0.0;
        sum += weight * color;
        weightSum += weight;    

        // Upperleft
        color = PassSrg::m_diffuseFrameBuffer.Sample(PassSrg::LinearSampler, IN.m_texCoord, int2(-1, -1)).rgb;
        weight = color.x + color.y + color.z > 0.0 ? 0.25 : 0.0;
        sum += weight * color;
        weightSum += weight;    

        diffuse = float4(sum / weightSum, 1.0);
    }

    float4 specular = PassSrg::m_specularFrameBuffer.Sample(PassSrg::LinearSampler, IN.m_texCoord);
    
    OUT.m_color = float4(diffuse.rgb, 1.0) + specular;

    return OUT;
}