robloo
4 years ago
2 changed files with 246 additions and 3 deletions
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using System; |
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using System.Globalization; |
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using Avalonia.Controls.Converters; |
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using Avalonia.Data.Converters; |
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using Avalonia.Media; |
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namespace Avalonia.Controls.Primitives.Converters |
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{ |
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/// <summary>
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/// Gets a <see cref="SolidColorBrush"/>, either black or white, depending on the luminance of the supplied color.
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/// A default color supplied in the converter parameter may be returned if alpha is below the set threshold.
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/// </summary>
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public class ContrastBrushConverter : IValueConverter |
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{ |
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private ToColorConverter toColorConverter = new ToColorConverter(); |
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/// <summary>
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/// Gets or sets the alpha channel threshold below which a default color is used instead of black/white.
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/// </summary>
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public byte AlphaThreshold { get; set; } = 128; |
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/// <inheritdoc/>
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public object? Convert( |
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object? value, |
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Type targetType, |
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object? parameter, |
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CultureInfo culture) |
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{ |
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Color comparisonColor; |
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Color? defaultColor = null; |
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// Get the changing color to compare against
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var convertedValue = toColorConverter.Convert(value, targetType, parameter, culture); |
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if (convertedValue is Color valueColor) |
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{ |
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comparisonColor = valueColor; |
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} |
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else |
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{ |
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// Invalid color value provided
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return AvaloniaProperty.UnsetValue; |
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} |
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// Get the default color when transparency is high
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var convertedParameter = toColorConverter.Convert(parameter, targetType, parameter, culture); |
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if (convertedParameter is Color parameterColor) |
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{ |
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defaultColor = parameterColor; |
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} |
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if (comparisonColor.A < AlphaThreshold && |
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defaultColor.HasValue) |
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{ |
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// If the transparency is less than the threshold, just use the default brush
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// This can commonly be something like the TextControlForeground brush
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return new SolidColorBrush(defaultColor.Value); |
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} |
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else |
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{ |
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// Chose a white/black brush based on contrast to the base color
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if (ColorHelper.GetRelativeLuminance(comparisonColor) <= 0.5) |
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{ |
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// Dark color, return light for contrast
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return new SolidColorBrush(Colors.White); |
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} |
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else |
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{ |
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// Bright color, return dark for contrast
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return new SolidColorBrush(Colors.Black); |
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} |
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} |
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} |
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/// <inheritdoc/>
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public object? ConvertBack( |
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object? value, |
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Type targetType, |
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object? parameter, |
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CultureInfo culture) |
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{ |
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return AvaloniaProperty.UnsetValue; |
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} |
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} |
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} |
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