组合纯色画笔

不幸的是,WPF中不支持自定义画笔(画笔类型标记为“Internal”,无法从继承),因此无法创建由两个画笔组成的混合画笔,该混合画笔可以像普通SolidColorBrush一样从XAML中使用。

作为解决方法,您可以使用markupextension来模拟自定义画笔的行为,这允许您使用XAML语法并提供自定义值,这允许我们使用内置的solidcolorbrush(不需要自定义画笔)设置为混合两种颜色时获得的值:

/// <summary>
/// Markup extension to mix two SolidColorBrushes together to produce a new SolidColorBrush.
/// </summary>
[MarkupExtensionReturnType(typeof(SolidColorBrush))]
public class MixedColorBrush : MarkupExtension, INotifyPropertyChanged
{
    /// <summary>
    /// The foreground mix color; defaults to white.  
    /// If not changed, the result will always be white.
    /// </summary>
    private SolidColorBrush foreground = Brushes.White;

    /// <summary>
    /// The background mix color; defaults to black.  
    /// If not set, the result will be the foreground color.
    /// </summary>
    private SolidColorBrush background = Brushes.Black;

    /// <summary>
    /// PropertyChanged event for WPF binding.
    /// </summary>
    public event PropertyChangedEventHandler PropertyChanged;

    /// <summary>
    /// Gets or sets the foreground mix color.
    /// </summary>
    public SolidColorBrush Foreground
    {
        get 
        { 
            return this.foreground; 
        }
        set 
        { 
            this.foreground = value; 
            this.NotifyPropertyChanged("Foreground"); 
        }
    }

    /// <summary>
    /// Gets or sets the background mix color.
    /// </summary>
    public SolidColorBrush Background
    {
        get 
        { 
            return this.background; 
        }
        set 
        { 
            this.background = value; 
            this.NotifyPropertyChanged("Background"); 
        }
    }

    /// <summary>
    /// Returns a SolidColorBrush that is set as the value of the 
    /// target property for this markup extension.
    /// </summary>
    /// <param name="serviceProvider">Object that can provide services for the markup extension.</param>
    /// <returns>The object value to set on the property where the extension is applied.</returns>
    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        if (this.foreground != null && this.background != null)
        {
            // Create a new brush as a composite of the old ones
            // This does simple non-perceptual additive color, e.g 
            // blue + red = magenta, but you can swap in a different
            // algorithm to do subtractive color (red + yellow = orange)
            return new SolidColorBrush(this.foreground.Color + this.background.Color);
        }

        // If either of the brushes was set to null, return an empty (white) brush.
        return new SolidColorBrush();
    }

    /// <summary>
    /// Raise the property changed event.
    /// </summary>
    /// <param name="propertyName">Name of the property which has changed.</param>
    protected void NotifyPropertyChanged(string propertyName)
    {
        if (this.PropertyChanged != null)
        {
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

然后可以像使用普通画笔一样从XAML中使用它:

<Grid>
    <Grid.Background>
        <local:MixedColorBrush Foreground="Blue" Background="Red"/>
    </Grid.Background>
</Grid>

或者使用标记扩展语法:

<Grid Background="{local:MixedColorBrush Foreground=Blue, Background=Red}">

这种方法的缺点是,不能使用DynamicResource或StaticResource引用将值绑定到应用程序中的其他资源。MarkupExtension不是DependencyObject,资源绑定只在DependencyObjects上工作;内置画笔是DependencyObjects,这就是绑定使用传统画笔的原因。

我也遇到了同样的问题。我通常只使用一个XAML,分别用于基本的暗色、基本的灯光,然后一个用于每个颜色的重音(蓝色、红色等)。强调是稍微看,这使它更暗时,然后选择较暗的主题与较暗的背景。

当用次要的强调色创建一个主题以在应用程序中具有更大的对比度时(例如,选择浅色主题时为灰色,选择深色主题时为强调色),我需要用两种颜色构建一个画笔,否则我将不得不为每种颜色创建一个深色和浅色主题。

我用的是:

<DrawingBrush x:Key="SecondaryAccentColorBrush" Viewport="0,0,1,1" TileMode="Tile">
    <DrawingBrush.Drawing>
        <DrawingGroup>
            <GeometryDrawing>
                <GeometryDrawing.Geometry>
                    <RectangleGeometry Rect="0,0,1,1" />
                </GeometryDrawing.Geometry>
                <GeometryDrawing.Brush>
                    <SolidColorBrush Color="{DynamicResource AccentColor}"/>
                </GeometryDrawing.Brush>
            </GeometryDrawing>
            <GeometryDrawing>
                <GeometryDrawing.Geometry>
                    <RectangleGeometry Rect="0,0,1,1" />
                </GeometryDrawing.Geometry>
                <GeometryDrawing.Brush>
                    <SolidColorBrush Color="{DynamicResource Gray10}"/>
                </GeometryDrawing.Brush>
            </GeometryDrawing>
        </DrawingGroup>
    </DrawingBrush.Drawing>
</DrawingBrush>

切换主题时,“gray10”的alpha在00和ff之间切换,因此画笔显示灰色或强调色。

从前景和背景画笔中获取颜色,混合它们,然后根据生成的颜色创建一个新的画笔。

C中的例子:

Color foreground = foregroundBrush.Color;
Color background = backgroundBrush.Color;

int opacity = 25;

int r = (opacity * (foreground.R - background.R) / 100) + background.R;
int g = (opacity * (foreground.G - background.G) / 100) + background.G;
int b = (opacity * (foreground.B - background.B) / 100) + background.B;

SolidColorBrush mixedBrush = new SolidColorBrush(Color.FromArgb(r, g, b));

一种简单的方法(但可能没有优化)。 创建一个 LinearGradientBrush 在两种颜色的重复模式中,端点等于起点:

<LinearGradientBrush SpreadMethod="Repeat" EndPoint="0,0">
                                <GradientStop Color="Red" Offset="0" />
                                <GradientStop Color="Yellow" Offset="1" />
                            </LinearGradientBrush>

这个给你一把橙色的刷子。