o3de/Gems/AtomTressFX/Assets/Shaders/HairFullScreenUtils.azsli

/*
* Modifications 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/PostProcessing/FullscreenVertexInfo.azsli>
#include <Atom/Features/PostProcessing/FullscreenVertexUtil.azsli>
#include <viewsrg_all.srgi>

//==============================================================================
// Generate a fullscreen triangle from pipeline provided vertex id 
VSOutput FullScreenVS(VSInput input)
{
    VSOutput OUT;

    float4 posTex = GetVertexPositionAndTexCoords(input.m_vertexID);

    OUT.m_texCoord = float2(posTex.z, posTex.w);    // [To Do] - test sign of Y based on original code
    OUT.m_position = float4(posTex.xy, 0.0, 1.0);

    return OUT;
}

//==============================================================================
// Given the depth buffer depth of the current pixel and the fragment XY position, 
// reconstruct the NDC.
// screenCoords - from 0.. dimension of the screen of the current pixel
// screenTexture - screen buffer texture representing the same resolution we work in
// sDepth - the depth buffer depth at the fragment location
// NDC - Normalized Device Coordinates = warped screen space ( -1.1, -1..1, 0..1 )
float3 ScreenPosToNDC( Texture2D<float> screenTexture, float2 screenCoords, float depth )
{ 
    uint2 dimensions;
    screenTexture.GetDimensions(dimensions.x, dimensions.y);
    float2 UV = saturate(screenCoords / dimensions.xy);

    float x = UV.x * 2.0f - 1.0f;
    float y = (1.0f - UV.y) * 2.0f - 1.0f;
    float3 NDC = float3(x, y, depth);

    return NDC;
}

// Given the depth buffer depth of the current pixel and the fragment XY position, 
// reconstruct the world space position
float3 ScreenPosToWorldPos( 
    Texture2D<float> screenTexture, float2 screenCoords, float depth, 
    inout float3 screenPosNDC )
{ 
    screenPosNDC = ScreenPosToNDC(screenTexture, screenCoords, depth);
    float4 projectedPos = float4(screenPosNDC, 1.0f);    // warped projected space [0..1]
    float4 positionVS = mul(ViewSrg::m_projectionMatrixInverse, projectedPos);
    positionVS /= positionVS.w; // notice the normalization factor - crucial! 
    float4 positionWS = mul(ViewSrg::m_viewMatrixInverse, positionVS);

    return positionWS.xyz;
}