o3de/Gems/Atom/Feature/Common/Assets/Shaders/PostProcessing/ModulateTexture.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>

ShaderResourceGroup PassSrg : SRG_PerPass
{
    Texture2D<float> m_modifier;
    RWTexture2D<float4> m_inputOutput;

    Sampler LinearSampler
    {
        MinFilter = Linear;
        MagFilter = Linear;
        MipFilter = Linear;
        AddressU = Clamp;
        AddressV = Clamp;
        AddressW = Clamp;
    };
}

[numthreads(16,16,1)]
void MainCS(uint3 dispatch_id: SV_DispatchThreadID)
{
    // Get output texture dimensions
    uint2 outputDimensions;
    PassSrg::m_inputOutput.GetDimensions(outputDimensions.x, outputDimensions.y);
    uint2 outPixel = dispatch_id.xy;

    // Early out
    if(outPixel.x >= outputDimensions.x || outPixel.y >= outputDimensions.y)
    {
        return;
    }
    
    // Calculate the size of a pixel in screen UV space
    float2 pixelSize = 1.0f / float2(outputDimensions.xy);

    // Want to sample at the center of the pixel, so we need a half pixel offset
    float2 halfPixelSize = pixelSize * 0.5f;

    // Sample the modifier texture
    float2 sampleUV = mad(float2(outPixel.xy), pixelSize, halfPixelSize);
    float modifier = PassSrg::m_modifier.SampleLevel(PassSrg::LinearSampler, sampleUV, 0).r;

    // Sample the output target
    float4 sampleColor = PassSrg::m_inputOutput[outPixel].rgba;

    // Apply the modifer as a simple multiplier
    sampleColor.rgb *= modifier.xxx;

    // Write the modified value to the target
    PassSrg::m_inputOutput[outPixel] = sampleColor;
}