Question

我想使用LinearGradientBrush用渐变填充画布上的矩形范围。问题是，我希望渐变在矩形的两边看起来都是一样的，无论矩形有多大。

我想要绘制的是这样的：

这是我的第一次尝试：

LinearGradientBrush brush = new LinearGradientBrush();
brush.SpreadMethod = GradientSpreadMethod.Reflect;
brush.GradientStops.Add(new GradientStop((Color)ColorConverter.ConvertFromString("#FF0000FF"), 0.0));
brush.GradientStops.Add(new GradientStop((Color)ColorConverter.ConvertFromString("#22FFFFFF"), 0.25));
brush.GradientStops.Add(new GradientStop((Color)ColorConverter.ConvertFromString("#22FFFFFF"), 0.75));
brush.GradientStops.Add(new GradientStop((Color)ColorConverter.ConvertFromString("#FF0000FF"), 1.00));
brush.StartPoint = new Point(0, 0);
brush.EndPoint = new Point(1, 0);

Rectangle rect = new Rectangle();            
rect.Width = 100;
rect.Height = 100;
rect.Fill = brush;
Canvas.SetLeft(rect, 50);
Canvas.SetTop(rect, 50);
MyCanvas.Children.Add(rect);

Rectangle rect2 = new Rectangle();
rect2.Width = 300;
rect2.Height = 100;
rect2.Fill = brush;
Canvas.SetLeft(rect2, 50);
Canvas.SetTop(rect2, 200);
MyCanvas.Children.Add(rect2);

不太对;矩形越大，渐变越宽：

我尝试将MappingMode设置为Absolute，但这也不起作用。

LinearGradientBrush brush = new LinearGradientBrush();
brush.MappingMode = BrushMappingMode.Absolute;
brush.SpreadMethod = GradientSpreadMethod.Reflect;

brush.GradientStops.Add(new GradientStop((Color)ColorConverter.ConvertFromString("#FF0000FF"), 0.0));
brush.GradientStops.Add(new GradientStop((Color)ColorConverter.ConvertFromString("#22FFFFFF"), 0.25));

brush.StartPoint = new Point(0, 0);
brush.EndPoint = new Point(50, 0);   //I want the gradient to be across 50 pixels

Rectangle rect = new Rectangle();    
//Everything else is the same

这给我一些看起来像这样的东西：

离开了。有什么建议吗？

Answer 1

实现此目的的一种方法是创建custom control 在Grid上用3个矩形组成它;

1列，宽50像素，矩形填充线性渐变
1列“内容”矩形填充剩余部分
1列，宽50像素，矩形填充线性渐变。

Answer 2

您可以使用将矩形的背景绑定到其ActualHeight并使用转换器，计算该宽度的百分比表示预期的宽度（使用绝对值，您也可以直接设置像素）：

class HeightToBrushComplexPropertyConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        double height = (double)value;
        double percent = 50.0 / height;

        LinearGradientBrush brush = new LinearGradientBrush();
        brush.StartPoint = new Point(0, 0);
        brush.EndPoint = new Point(1, 0);

        brush.MappingMode = BrushMappingMode.RelativeToBoundingBox;
        brush.SpreadMethod = GradientSpreadMethod.Pad;

        brush.GradientStops.Add(new GradientStop((Color)ColorConverter.ConvertFromString("#FF0000FF"), 0.0));
        brush.GradientStops.Add(new GradientStop((Color)ColorConverter.ConvertFromString("#22FFFFFF"), percent));
        brush.GradientStops.Add(new GradientStop((Color)ColorConverter.ConvertFromString("#22FFFFFF"), 1 - percent));
        brush.GradientStops.Add(new GradientStop((Color)ColorConverter.ConvertFromString("#FF0000FF"), 1));

        return brush;

    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

对此转换器进行改进：接受像素数和颜色作为参数。

LinearGradientBrush，两端都有固定宽度的渐变

2 个答案: