o3de/Gems/Atom/Feature/Common/Assets/Shaders/Reflections/ReflectionComposite.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
 *
 */

// Specular IBL reflection pipeline:
// Stencil -> BlendWeight -> GlobalFullscreen -> RenderOuter -> RenderInner -> Composite
//                                                                             ---------
// 
// This shader composites the final reflection texture onto the specular texture using a
// fullscreen pass, for pixels that have a non-zero stencil value.  Output values are
// box-filtered from the MSAA sub-pixels of the reflection texture.

#include <scenesrg_all.srgi>

#include <Atom/Features/Debug.azsli>

#include <Atom/Features/PostProcessing/FullscreenVertexUtil.azsli>
#include <Atom/Features/PostProcessing/FullscreenVertexInfo.azsli>
#include <Atom/Features/PostProcessing/FullscreenPixelInfo.azsli>

ShaderResourceGroup PassSrg : SRG_PerPass_WithFallback
{
    Texture2DMS<float4>  m_reflection;
}

// 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)
{
    if(!IsSpecularLightingEnabled() || !IsIndirectLightingEnabled())
    {
        PSOutput OUT;
        OUT.m_color = float4(0, 0, 0, 0);
        return OUT;
    }

    // read reflection image, box filter samples for MSAA
    // Note: output will only be written to the sub-pixel samples that pass the stencil test
    float3 reflection = float3(0.0f, 0.0f, 0.0f);

    uint width, height, samples;
    PassSrg::m_reflection.GetDimensions(width, height, samples);
    for (uint sampleIndex = 0; sampleIndex < samples; ++sampleIndex)
    {
        reflection += PassSrg::m_reflection.Load(IN.m_position.xy, sampleIndex).rgb;
    }

    reflection /= samples;
    
    PSOutput OUT;
    OUT.m_color = float4(reflection, 1.0f);
    return OUT;
}