如何:向绘图应用不透明遮罩

更新:2007 年 11 月

此示例演示如何向 Drawing 应用不透明蒙板。DrawingGroup 类是仅有的支持不透明蒙板的 Drawing 对象类型。

若要向 Drawing 对象应用不透明蒙板,请将其添加到 DrawingGroup,并设置 DrawingGroup 对象的 OpacityMask 属性。

下面的插图显示了 DrawingGroup 的三个视图:不带不透明蒙板的绘图、单独的不透明蒙板以及应用不透明蒙板后的 DrawingGroup

具有不透明遮罩的 DrawingGroup

示例

下面的示例将 RadialGradientBrush 用作 DrawingGroup 的不透明蒙板。

说明:

虽然此示例使用 RadialGradientBrush 作为不透明蒙板,但 LinearGradientBrushDrawingBrushImageBrushVisualBrush 对象可以构成良好的不透明蒙板。有关不透明蒙板及其工作原理的更多信息,请参见不透明遮罩概述

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace SDKSample
{
    /// <summary>
    /// Shows how to create and apply an OpacityMask to
    /// a DrawinGroup.
    /// </summary>
    public class OpacityMaskExample : Page
    {
        public OpacityMaskExample()
        {

            //
            // Create a GeometryDrawing.
            //

            // Define the drawing's contents.
            PathFigure pLineFigure = new PathFigure();
            pLineFigure.StartPoint = new Point(25, 25);
            PolyLineSegment pLineSegment = new PolyLineSegment();
            pLineSegment.Points.Add(new Point(0, 50));
            pLineSegment.Points.Add(new Point(25, 75));
            pLineSegment.Points.Add(new Point(50, 50));
            pLineSegment.Points.Add(new Point(25, 25));
            pLineSegment.Points.Add(new Point(25, 0));
            pLineFigure.Segments.Add(pLineSegment);
            PathGeometry pGeometry = new PathGeometry();
            pGeometry.Figures.Add(pLineFigure);

            GeometryDrawing drawing1 = new GeometryDrawing(
                    Brushes.Lime,
                    new Pen(Brushes.Black, 10),
                    pGeometry
                );

            //
            // Create another GeometryDrawing.
            //
            GeometryDrawing drawing2 = new GeometryDrawing(
                    Brushes.Lime,
                    new Pen(Brushes.Black, 2),
                    new EllipseGeometry(new Point(10, 10), 5, 5)
                );

            // Create the DrawingGroup and add the
            // geometry drawings.
            DrawingGroup aDrawingGroup = new DrawingGroup();
            aDrawingGroup.Children.Add(drawing1);
            aDrawingGroup.Children.Add(drawing2);

            //
            // Define an opacity mask and apply it to the
            // drawing group.
            //
            RadialGradientBrush opacityMask = new RadialGradientBrush();
            opacityMask.GradientStops.Add(new GradientStop(Color.FromArgb(255, 0, 0, 0), 0.0));
            opacityMask.GradientStops.Add(new GradientStop(Color.FromArgb(0, 0, 0, 0), 0.55));
            opacityMask.GradientStops.Add(new GradientStop(Color.FromArgb(255, 0, 0, 0), 0.65));
            opacityMask.GradientStops.Add(new GradientStop(Color.FromArgb(0, 0, 0, 0), 0.75));
            opacityMask.GradientStops.Add(new GradientStop(Color.FromArgb(255, 0, 0, 0), 0.80));
            opacityMask.GradientStops.Add(new GradientStop(Color.FromArgb(0, 0, 0, 0), 0.90));
            opacityMask.GradientStops.Add(new GradientStop(Color.FromArgb(255, 0, 0, 0), 1.0));

            aDrawingGroup.OpacityMask = opacityMask;


            // Use an Image control and a DrawingImage to
            // display the drawing.
            DrawingImage aDrawingImage = new DrawingImage(aDrawingGroup);

            // Freeze the DrawingImage for performance benefits.
            aDrawingImage.Freeze();

            Image anImage = new Image();
            anImage.Source = aDrawingImage;
            anImage.Stretch = Stretch.None;
            anImage.HorizontalAlignment = HorizontalAlignment.Left;

            // Create a border around the images and add it to the
            // page.
            Border imageBorder = new Border();
            imageBorder.BorderBrush = Brushes.Gray;
            imageBorder.BorderThickness = new Thickness(1);
            imageBorder.VerticalAlignment = VerticalAlignment.Top;
            imageBorder.HorizontalAlignment = HorizontalAlignment.Left;
            imageBorder.Margin = new Thickness(20);
            imageBorder.Child = anImage;

            this.Background = Brushes.White;
            this.Margin = new Thickness(20);
            this.Content = imageBorder;

        }
    }
}
<Page 
  xmlns="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="https://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:PresentationOptions="https://schemas.microsoft.com/winfx/2006/xaml/presentation/options" 
  xmlns:mc="https://schemas.openxmlformats.org/markup-compatibility/2006"
  mc:Ignorable="PresentationOptions"
  Margin="20" Background="White">
  <Border BorderBrush="Gray" BorderThickness="1" 
    HorizontalAlignment="Left" VerticalAlignment="Top" Margin="20">
    <Image Stretch="None" HorizontalAlignment="Left">
      <Image.Source>
        <DrawingImage PresentationOptions:Freeze="True">
          <DrawingImage.Drawing>

            <!-- A DrawingGroup with a RadialGradientBrush as its opacity mask. -->
            <DrawingGroup>
              <GeometryDrawing Brush="Lime" Geometry="M 25,25 L 0,50 25,75 50,50 25,25 25,0">
                <GeometryDrawing.Pen>
                  <Pen Thickness="10" Brush="Black" />
                </GeometryDrawing.Pen>
              </GeometryDrawing>
              <GeometryDrawing Brush="Lime">
                <GeometryDrawing.Geometry>
                  <EllipseGeometry Center="10,10" RadiusX="5" RadiusY="5" />
                </GeometryDrawing.Geometry>
                <GeometryDrawing.Pen>
                  <Pen Thickness="2" Brush="Black" />
                </GeometryDrawing.Pen>
              </GeometryDrawing>
              <DrawingGroup.OpacityMask>

                <!-- The opacity mask. -->
                <RadialGradientBrush>
                  <GradientStop Offset="0.0" Color="#FF000000" />
                  <GradientStop Offset="0.55" Color="#00000000" />
                  <GradientStop Offset="0.65" Color="#FF000000" />
                  <GradientStop Offset="0.75" Color="#00000000" />
                  <GradientStop Offset="0.80" Color="#FF000000" />
                  <GradientStop Offset="0.90" Color="#00000000" />
                  <GradientStop Offset="1.0" Color="#FF000000" />
                </RadialGradientBrush>
              </DrawingGroup.OpacityMask>
            </DrawingGroup>
          </DrawingImage.Drawing>
        </DrawingImage>
      </Image.Source>
    </Image>
  </Border>


</Page>

请参见

概念

Drawing 对象概述

不透明遮罩概述

参考

DrawingGroup.OpacityMask