/*****************************************************************************
 * Copyright (C) 2022 VLC authors and VideoLAN
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
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 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
 *****************************************************************************/

/****************************************************************************
**
** Copyright (C) 2015 The Qt Company Ltd.
** Contact: http://www.qt.io/licensing/
**
** This file is part of the Qt Graphical Effects module.
**
** $QT_BEGIN_LICENSE:BSD$
** You may use this file under the terms of the BSD license as follows:
**
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** modification, are permitted provided that the following conditions are
** met:
**   * Redistributions of source code must retain the above copyright
**     notice, this list of conditions and the following disclaimer.
**   * Redistributions in binary form must reproduce the above copyright
**     notice, this list of conditions and the following disclaimer in
**     the documentation and/or other materials provided with the
**     distribution.
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**     contributors may be used to endorse or promote products derived
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**
** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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****************************************************************************/

//blending formulas are taken from Qt's Blend.qml implementation

varying mediump vec2 qt_TexCoord0;
uniform highp float qt_Opacity;
uniform lowp sampler2D backgroundSource;
uniform lowp vec4 screenColor;
uniform lowp vec4 overlayColor;

lowp vec4 fromPremult(lowp vec4 color) {
    lowp vec4 result = vec4(0.0);
    result.rgb = color.rgb / max(1.0/256.0, color.a);
    result.a = color.a;
    return result;
}

lowp vec4 toPremult(lowp vec4 color) {
    lowp vec4 result = vec4(0.0);
    result.rbg = color.rbg * color.a;
    result.a = color.a;
    return result;
}

lowp vec4 screen(lowp vec4 color1, lowp vec4 color2) {
    lowp vec4 result = vec4(0.0);
    highp float a = max(color1.a, color1.a * color2.a);

    result.rgb = 1.0 - (vec3(1.0) - color1.rgb) * (vec3(1.0) - color2.rgb);

    result.rgb = mix(color1.rgb, result.rgb, color2.a);
    result.a = max(color1.a, color1.a * color2.a);
    return result;
}

lowp vec4 multiply(lowp vec4 color1, lowp vec4 color2) {
    lowp vec4 result = vec4(0.0);

    result.rgb = color1.rgb * color2.rgb;

    result.rgb = mix(color1.rgb, result.rgb, color2.a);
    result.a = max(color1.a, color1.a * color2.a);
    return result;
}

lowp vec4 normal(lowp vec4 color1, lowp vec4 color2) {
    lowp vec4 result = vec4(0.0);
    result.rgb = mix(color1.rgb, color2.rgb, color2.a);
    result.a = max(color1.a, color2.a);
    return result;
}

void main() {
    lowp vec4 result = vec4(0.0);
    lowp vec4 colorP = fromPremult(texture2D(backgroundSource, qt_TexCoord0));
    lowp vec4 screenColorP = fromPremult(screenColor);
    lowp vec4 overlayColorP = fromPremult(overlayColor);

    result = screen(colorP, screenColorP);
    result = multiply(result, screenColorP);
    result = normal(result, overlayColorP);

    gl_FragColor = vec4(result.rgb, 1.0) * qt_Opacity;
}
