o3de/Gems/Atom/Feature/Common/Assets/Shaders/PostProcessing/DepthDownsample.azsl

/*
 * 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>

#define THREADS 16

ShaderResourceGroup PassSrg : SRG_PerPass
{
    Texture2D<float> m_depthFullRes;
    RWTexture2D<float> m_depthHalfRes;
}

[numthreads(THREADS, THREADS, 1)]
void MainCS(uint3 dispatch_id: SV_DispatchThreadID)
{  
    uint2 targetPixel = dispatch_id.xy;

    // Take the upper left pixel in the 2x2 quad. This has two advantages:
    // 1) It gives us a real depth value instead of an averaged depth
    // 2) It preserves equal distance properties between pixels (necessary for SSAO)
    uint2 sourcePixel = targetPixel * 2;

    PassSrg::m_depthHalfRes[targetPixel] = PassSrg::m_depthFullRes[sourcePixel];
}