o3de/Gems/AtomTressFX/Assets/Shaders/HairUtilities.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) AND MIT
 *
 */

//---------------------------------------------------------------------------------------
// Shader code utilities for TressFX
//-------------------------------------------------------------------------------------
//
// Copyright (c) 2019 Advanced Micro Devices, Inc. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//
// Cutoff to not render hair

#pragma once

#define SHORTCUT_MIN_ALPHA 0.02

#define TRESSFX_FLOAT_EPSILON 1e-7

//--------------------------------------------------------------------------------------
//
//     Controls whether you do mul(M,v) or mul(v,M)
//     i.e., row major vs column major
//
//--------------------------------------------------------------------------------------
float4 MatrixMult(float4x4 m, float4 v)
{
    return mul(m, v);
}

// Pack a float4 into an uint
uint PackFloat4IntoUint(float4 vValue)
{
    return (((uint)(vValue.x * 255)) << 24) | (((uint)(vValue.y * 255)) << 16) | (((uint)(vValue.z * 255)) << 8) | (uint)(vValue.w * 255);
}

// Unpack a uint into a float4 value
float4 UnpackUintIntoFloat4(uint uValue)
{
    return float4(((uValue & 0xFF000000) >> 24) / 255.0, ((uValue & 0x00FF0000) >> 16) / 255.0, ((uValue & 0x0000FF00) >> 8) / 255.0, ((uValue & 0x000000FF)) / 255.0);
}

// Pack a float3 and a uint8 into an uint
uint PackFloat3ByteIntoUint(float3 vValue, uint uByteValue)
{
    return (((uint)(vValue.x * 255)) << 24) | (((uint)(vValue.y * 255)) << 16) | (((uint)(vValue.z * 255)) << 8) | uByteValue;
}

// Unpack a uint into a float3 and a uint8 value
float3 UnpackUintIntoFloat3Byte(uint uValue, out uint uByteValue)
{
    uByteValue = uValue & 0x000000FF;
    return float3(((uValue & 0xFF000000) >> 24) / 255.0, ((uValue & 0x00FF0000) >> 16) / 255.0, ((uValue & 0x0000FF00) >> 8) / 255.0);
}

//--------------------------------------------------------------------------------------
//
//      Safe_normalize-float2
//
//--------------------------------------------------------------------------------------
float2 Safe_normalize(float2 vec)
{
    float len = length(vec);
    return len >= TRESSFX_FLOAT_EPSILON ? (vec * rcp(len)) : float2(0, 0);
}

//--------------------------------------------------------------------------------------
//
//      Safe_normalize-float3
//
//--------------------------------------------------------------------------------------
float3 Safe_normalize(float3 vec)
{
    float len = length(vec);
    return len >= TRESSFX_FLOAT_EPSILON ? (vec * rcp(len)) : float3(0, 0, 0);
}

//--------------------------------------------------------------------------------------
// ComputeCoverage
//
// Calculate the pixel coverage of a hair strand by computing the hair width
//--------------------------------------------------------------------------------------
float ComputeCoverage(float2 p0, float2 p1, float2 pixelLoc, float2 winSize)
{
    // p0, p1, pixelLoc are in d3d clip space (-1 to 1)x(-1 to 1)

    // Scale positions so 1.f = half pixel width
    p0 *= winSize;
    p1 *= winSize;
    pixelLoc *= winSize;

    float p0dist = length(p0 - pixelLoc);
    float p1dist = length(p1 - pixelLoc);
    float hairWidth = length(p0 - p1);

    // will be 1.f if pixel outside hair, 0.f if pixel inside hair
    float outside = any(float2(step(hairWidth, p0dist), step(hairWidth, p1dist)));

    // if outside, set sign to -1, else set sign to 1
    float sign = outside > 0.f ? -1.f : 1.f;

    // signed distance (positive if inside hair, negative if outside hair)
    float relDist = sign * saturate(min(p0dist, p1dist));

    // returns coverage based on the relative distance
    // 0, if completely outside hair edge
    // 1, if completely inside hair edge
    return (relDist + 1.f) * 0.5f;
}