/***********************************************************/

/* Shader author: Foxioo and Adam Hawker (aka Sketchy / MuddyMole) */
/* Version shader: 1.0 (11.11.2025) */
/* My GitHub: https://github.com/FoxiooOfficial */

/***********************************************************/

/***********************************************************/
/* Samplers */
/***********************************************************/

Texture2D<float4> S2D_Image : register(t0);
SamplerState S2D_ImageSampler : register(s0);

Texture2D<float4> S2D_Background : register(t1);
SamplerState S2D_BackgroundSampler : register(s1);

/***********************************************************/
/* Variables */
/***********************************************************/

cbuffer PS_VARIABLES : register(b0)
{
    bool _;
    float xA;
    float yA;
    float xB;
    float yB;
    float xC;
    float yC;
    float xD;
    float yD;
    bool __;
};

struct PS_INPUT
{
    float4 Tint : COLOR0;
    float2 texCoord : TEXCOORD0;
};

struct PS_OUTPUT
{
    float4 Color : SV_TARGET;
};

/************************************************************/
/* Main */
/************************************************************/

float2 Fun_Quad(float2 UV)
{
    /*
    float a = (xA - UV.x) * (yB - UV.y) - (xB - UV.x) * (yA - UV.y);
    float b = (xB - UV.x) * (yC - UV.y) - (xC - UV.x) * (yB - UV.y);
    float c = (xC - UV.x) * (yD - UV.y) - (xD - UV.x) * (yC - UV.y);
    float d = (xD - UV.x) * (yA - UV.y) - (xA - UV.x) * (yD - UV.y);

    if (sign(a)==sign(b) && sign(b)==sign(c) && sign(c)==sign(d))
    {
    */
        float a1 = xA;
        float a2 = xB - xA;
        float a3 = xD - xA;
        float a4 = xA - xB + xC - xD;

        float b1 = yA;
        float b2 = yB - yA;
        float b3 = yD - yA;
        float b4 = yA - yB + yC - yD;

        float aa = a4 * b3 - a3 * b4;
        float bb = a4 * b1 - a1 * b4 + a2 * b3 - a3 * b2 + UV.x * b4 - UV.y * a4;
        float cc = a2 * b1 - a1 * b2 + UV.x * b2 - UV.y * a2;

            float eps = 1e-6;
            float m;

                if (abs(aa) < eps) { m = -cc / bb; }
                else
                {
                    float det = sqrt(bb*bb - 4.0*aa*cc);
                    m = (-bb + det) / (2.0 * aa);
                }

        float denom = a2 + a4 * m;
        float l = (UV.x - a1 - a3 * m) / denom;

        return float2(l, m);
    /*
    }
    else return -1;*/
}

PS_OUTPUT ps_main(in PS_INPUT In)
{
    PS_OUTPUT Out;

    float2 _In = Fun_Quad(In.texCoord);

    float4 _Render_Texture =  S2D_Image.Sample(S2D_ImageSampler, _In)* In.Tint;

    Out.Color = _Render_Texture;
    return Out;
}

/***********************************************************/
/* Premultiplied Alpha */
/***********************************************************/

float4 Demultiply(float4 _color)
{
    if (_color.a != 0)
        _color.rgb /= _color.a;
    return _color;
}

PS_OUTPUT ps_main_pm(in PS_INPUT In)
{
    PS_OUTPUT Out;

    float2 _In = Fun_Quad(In.texCoord);

    float4 _Render_Texture =  Demultiply(S2D_Image.Sample(S2D_ImageSampler, _In)) * In.Tint;

        _Render_Texture.rgb *= _Render_Texture.a;

    Out.Color = _Render_Texture;
    return Out;
}
