// SPDX-License-Identifier: (Not available for this version, you are only allowed to use this software if you have express permission from the copyright holder and agreed to the latest NiloToonURP EULA)
// Copyright (c) 2021 Kuroneko ShaderLab Limited

// For more information, visit -> https://github.com/ColinLeung-NiloCat/UnityURPToonLitShaderExample

// #pragma once is a safe guard best practice in almost every .hlsl, 
// doing this can make sure your .hlsl's user can include this .hlsl anywhere anytime without producing any multi include conflict
#pragma once

// this will NOT work for iPhone15Pro, why?
// likely due to dynamic array indexing or % operator can't compile correctly for A17 Pro chip.
// This is possibly a Unity/Metal shader compiler bug that we can't fix (need to wait for Unity/Apple to fix).
/*
void NiloDoDitherFadeoutClip(float2 SV_POSITIONxy, float ditherOpacity)
{
    // copy from https://docs.unity3d.com/Packages/com.unity.shadergraph@10.3/manual/Dither-Node.html?q=dither
    float DITHER_THRESHOLDS[16] =
    {
        1.0 / 17.0,  9.0 / 17.0,  3.0 / 17.0, 11.0 / 17.0,
        13.0 / 17.0,  5.0 / 17.0, 15.0 / 17.0,  7.0 / 17.0,
        4.0 / 17.0, 12.0 / 17.0,  2.0 / 17.0, 10.0 / 17.0,
        16.0 / 17.0,  8.0 / 17.0, 14.0 / 17.0,  6.0 / 17.0
    };
    uint index = (uint(SV_POSITIONxy.x) % 4) * 4 + uint(SV_POSITIONxy.y) % 4;
    clip(ditherOpacity - DITHER_THRESHOLDS[index]);
}
*/

// This workaround WILL work for iPhone 15 Pro and all other devices
// Removed dynamic array indexing and % operator, replaced with unrolled if-else chain
// Tested on: Unity Editor, iPhone 14/15, iPhone 15 Pro
// Should be 100% safe and produces identical results to the original code
void NiloDoDitherFadeoutClip(float2 SV_POSITIONxy, float ditherOpacity)
{
    // Floor pixel coordinates and cast to int (robust even with negative positions)
    // Floor is safer for edge cases (if SV_POSITIONxy is somehow negative, which is not expected)
    int2 ip = (int2)floor(SV_POSITIONxy);
    int x = ip.x & 3;
    int y = ip.y & 3;
   
    // Bitshift is semantically clearer (x * 4 = x << 2)
    float threshold;
    int index = (x << 2) | y;

    // Unrolled lookup
    if (index == 0) threshold = 1.0 / 17.0;
    else if (index == 1) threshold = 9.0 / 17.0;
    else if (index == 2) threshold = 3.0 / 17.0;
    else if (index == 3) threshold = 11.0 / 17.0;
    else if (index == 4) threshold = 13.0 / 17.0;
    else if (index == 5) threshold = 5.0 / 17.0;
    else if (index == 6) threshold = 15.0 / 17.0;
    else if (index == 7) threshold = 7.0 / 17.0;
    else if (index == 8) threshold = 4.0 / 17.0;
    else if (index == 9) threshold = 12.0 / 17.0;
    else if (index == 10) threshold = 2.0 / 17.0;
    else if (index == 11) threshold = 10.0 / 17.0;
    else if (index == 12) threshold = 16.0 / 17.0;
    else if (index == 13) threshold = 8.0 / 17.0;
    else if (index == 14) threshold = 14.0 / 17.0;
    else threshold = 6.0 / 17.0;
   
    clip(ditherOpacity - threshold);
}