packages/MaterialDesignThemes.2.5.1/src/net45/Converters/BrushRoundConverter.cs

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using System;
using System.Globalization;
using System.Windows.Data;
using System.Windows.Media;

namespace MaterialDesignThemes.Wpf.Converters
{
    public class BrushRoundConverter : IValueConverter
    {
        public Brush HighValue { get; set; } = Brushes.White;

        public Brush LowValue { get; set; } = Brushes.Black;

        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {            
            var solidColorBrush = value as SolidColorBrush;
            if (solidColorBrush == null) return null;

            var color = solidColorBrush.Color;

            var brightness = 0.3 * color.R + 0.59 * color.G + 0.11 * color.B;

            return brightness < 123 ? LowValue : HighValue;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return Binding.DoNothing;
        }
    }
}