darkPaletteShader for Qt Telegram Chat discussion

darkPaletteShader.qml

        SystemPalette {
            id: defaultPalette
            colorGroup: SystemPalette.Active
            property color backgroundColor: defaultPalette.window
            property bool backgroundColorIsDark: backgroundColor.hslLightness < 0.5
                                                 || backgroundColor.hslSaturation < -0.8
        }

        ShaderEffect {
            enabled: false
            anchors.fill: img
            property variant src: img
            property alias backgroundColorIsDark: defaultPalette.backgroundColorIsDark

            vertexShader: "
uniform highp mat4 qt_Matrix;
attribute highp vec4 qt_Vertex;
attribute highp vec2 qt_MultiTexCoord0;
varying highp vec2 coord;
void main() {
coord = qt_MultiTexCoord0;
gl_Position = qt_Matrix * qt_Vertex;
}"
            fragmentShader: "
varying highp vec2 coord;
uniform sampler2D src;
uniform lowp float qt_Opacity;
uniform bool backgroundColorIsDark;

vec3 brightnessContrast(vec3 value, float brightness, float contrast)
{
return value * contrast + brightness;
}

void main() {
lowp vec4 tex = texture2D(src, coord);

if (tex.r==float(102.0/255.0) && tex.g==float(72.0/255.0) && tex.b==float(72.0/255.0) && backgroundColorIsDark)
gl_FragColor = vec4(vec3(1.1-tex.r,1.1-tex.g,1.1-tex.b),tex.a) * qt_Opacity;
else
gl_FragColor = tex.rgba;

if (backgroundColorIsDark) {
gl_FragColor = vec4(brightnessContrast(gl_FragColor.rgb,-0.3,1.4),tex.a) * qt_Opacity;
}

}"
        }