Tom Edwards
3 days ago
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GitHub
GitHub
18 changed files with 376 additions and 73 deletions
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using System; |
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namespace Avalonia; |
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/// <summary>
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/// Represents an object which can algoritmically scale text.
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/// </summary>
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public interface ITextScaler |
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{ |
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double GetScaledFontSize(Visual target, double baseFontSize); |
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/// <summary>
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/// Raised when the text scaling algorithm has changed. Indicates that all text should be rescaled.
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/// </summary>
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event EventHandler<EventArgs>? TextScalingChanged; |
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} |
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namespace Avalonia.Controls; |
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/// <summary>
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/// Represents an object which particpates in <see cref="TextScaling"/>.
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/// </summary>
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/// <seealso cref="ITextScaler"/>
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public interface ITextScaleable |
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{ |
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/// <summary>
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/// Called when the active text scaling algorithm for this object changes.
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/// </summary>
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void OnTextScalingChanged(); |
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} |
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using System; |
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using System.Collections.Generic; |
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using System.Runtime.CompilerServices; |
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using Avalonia.Controls.Documents; |
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using Avalonia.Threading; |
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namespace Avalonia.Controls; |
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/// <summary>
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/// Configures and computes text scaling. This is an accessibility feature which allows the user to request that text be
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/// drawn at a different size than normal, without altering other UI elements. The default scaling algorithm is determined
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/// by the platform and may make text smaller as well as larger.
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/// </summary>
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/// <remarks>
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/// Text scaling is applied when text is measured. It does not modify the value of <see cref="TextElement.FontSize"/>.
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/// </remarks>
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/// <seealso cref="ITextScaleable"/>
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/// <seealso cref="ITextScaler"/>
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public static class TextScaling |
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{ |
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private static readonly ConditionalWeakTable<ITextScaler, HashSet<Visual>> s_customTextScalerSubscribers = []; |
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/// <summary>
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/// Determines whether <see cref="TextElement.FontSize"/> (along with <see cref="TextElement.LetterSpacing"/>, <see cref="TextBlock.LineHeight"/>, and
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/// <see cref="TextBlock.LineSpacing"/>) should be scalled by calling <see cref="GetScaledFontSize"/> when measuring text content. The value is inherited.
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/// </summary>
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/// <remarks>Text scaling is typically not uniform. Smaller text scales up faster than larger text.</remarks>
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public static readonly AttachedProperty<bool> IsEnabledProperty = |
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AvaloniaProperty.RegisterAttached<Visual, bool>("IsEnabled", typeof(TextScaling), inherits: true); |
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/// <summary>
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/// Determines the minimum size (in em units) to which text will be scaled by <see cref="GetScaledFontSize"/>. The value is inherited.
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/// </summary>
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/// <remarks>This value is used only when <see cref="IsEnabledProperty"/> is true.</remarks>
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public static readonly AttachedProperty<double> MinFontSizeProperty = |
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AvaloniaProperty.RegisterAttached<Visual, double>("MinFontSize", typeof(TextScaling), inherits: true, validate: size => size >= 0); |
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/// <summary>
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/// Determines the maximum size (in em units) to which text will be scaled by <see cref="GetScaledFontSize"/>. The value is inherited.
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/// </summary>
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/// <remarks>This value is used only when <see cref="IsEnabledProperty"/> is true.</remarks>
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public static readonly AttachedProperty<double> MaxFontSizeProperty = |
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AvaloniaProperty.RegisterAttached<Visual, double>("MaxFontSize", typeof(TextScaling), defaultValue: double.PositiveInfinity, inherits: true, |
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validate: size => size > 0); |
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/// <summary>
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/// Determines a user-defined text scaling algorithm, which overrides platform text scaling in <see cref="GetScaledFontSize"/>. The value is inherited.
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/// </summary>
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/// <remarks>This value is used only when <see cref="IsEnabledProperty"/> is true.</remarks>
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public static readonly AttachedProperty<ITextScaler?> CustomTextScalerProperty = |
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AvaloniaProperty.RegisterAttached<Visual, ITextScaler?>("CustomTextScaler", typeof(TextScaling), inherits: true); |
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/// <inheritdoc cref="IsEnabledProperty"/> <see cref="IsEnabledProperty"/>
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public static bool GetIsEnabled(Visual visual) => visual.GetValue(IsEnabledProperty); |
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/// <inheritdoc cref="IsEnabledProperty"/> <see cref="IsEnabledProperty"/>
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public static void SetIsEnabled(Visual visual, bool value) => visual.SetValue(IsEnabledProperty, value); |
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/// <inheritdoc cref="MinFontSizeProperty"/> <see cref="MinFontSizeProperty"/>
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public static double GetMinFontSize(Visual visual) => visual.GetValue(MinFontSizeProperty); |
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/// <inheritdoc cref="MinFontSizeProperty"/> <see cref="MinFontSizeProperty"/>
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public static void SetMinFontSize(Visual visual, double value) => visual.SetValue(MinFontSizeProperty, value); |
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/// <inheritdoc cref="MaxFontSizeProperty"/> <see cref="MaxFontSizeProperty"/>
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public static double GetMaxFontSize(Visual visual) => visual.GetValue(MaxFontSizeProperty); |
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/// <inheritdoc cref="MaxFontSizeProperty"/> <see cref="MaxFontSizeProperty"/>
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public static void SetMaxFontSize(Visual visual, double value) => visual.SetValue(MaxFontSizeProperty, value); |
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/// <inheritdoc cref="CustomTextScalerProperty"/> <see cref="CustomTextScalerProperty"/>
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public static ITextScaler? GetCustomTextScaler(Visual visual) => visual.GetValue(CustomTextScalerProperty); |
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/// <inheritdoc cref="CustomTextScalerProperty"/> <see cref="CustomTextScalerProperty"/>
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public static void SetCustomTextScaler(Visual visual, ITextScaler? value) => visual.SetValue(CustomTextScalerProperty, value); |
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static TextScaling() |
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{ |
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CustomTextScalerProperty.Changed.AddClassHandler<Visual>(OnCustomTextScalerChanged); |
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} |
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private static void OnCustomTextScalerChanged(Visual visual, AvaloniaPropertyChangedEventArgs args) |
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{ |
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if (visual is not ITextScaleable) |
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{ |
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return; |
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} |
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var (oldScaler, newScaler) = args.GetOldAndNewValue<ITextScaler?>(); |
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if (oldScaler != null && s_customTextScalerSubscribers.TryGetValue(oldScaler, out var oldSubscribers)) |
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{ |
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oldSubscribers.Remove(visual); |
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} |
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if (newScaler != null) |
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{ |
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if (s_customTextScalerSubscribers.TryGetValue(newScaler, out var newSubscribers)) |
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{ |
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newSubscribers.Add(visual); |
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} |
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else |
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{ |
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s_customTextScalerSubscribers.Add(newScaler, [visual]); |
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newScaler.TextScalingChanged += OnCustomTextScalingChanged; |
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} |
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} |
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} |
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private static void OnCustomTextScalingChanged(object? sender, EventArgs e) |
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{ |
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Dispatcher.UIThread.VerifyAccess(); |
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if (sender is ITextScaler scaler && s_customTextScalerSubscribers.TryGetValue(scaler, out var subscribers)) |
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{ |
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foreach (var visual in subscribers) |
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{ |
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if (GetIsEnabled(visual)) |
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{ |
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((ITextScaleable)visual).OnTextScalingChanged(); |
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} |
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} |
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} |
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} |
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/// <summary>
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/// Scales <paramref name="baseFontSize"/> according to either the current platform text scaling rules, or the rules
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/// defined by the object assigned to <see cref="CustomTextScalerProperty"/> for <paramref name="visual"/>.
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/// </summary>
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/// <remarks>The values of <see cref="IsEnabledProperty"/>, <see cref="MinFontSizeProperty"/>, and <see cref="MaxFontSizeProperty"/>
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/// are enforced, even when <see cref="CustomTextScalerProperty"/> is in use.</remarks>
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public static double GetScaledFontSize(Visual visual, double baseFontSize) |
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{ |
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if (double.IsNaN(baseFontSize) || baseFontSize <= 0 || !GetIsEnabled(visual) || |
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(GetCustomTextScaler(visual) ?? TopLevel.GetTopLevel(visual)?.PlatformSettings) is not { } scaler) |
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{ |
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return baseFontSize; |
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} |
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// Extend min/max to encompass the base size. Conveniently, this means that min > max is not possible.
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var min = Math.Min(GetMinFontSize(visual), baseFontSize); |
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var max = Math.Max(GetMaxFontSize(visual), baseFontSize); |
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return Math.Clamp(scaler.GetScaledFontSize(visual, baseFontSize), min, max); |
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} |
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} |
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