如何：保持背景图像的长宽比

更新：2007 年 11 月

下面的示例演示如何使用 ImageBrush 的 Stretch 属性来保持图像的纵横比。

默认情况下，当您使用 ImageBrush 绘制某个区域时，该区域的内容将进行拉伸以完全填充输出区域。当输出区域和图像的纵横比不同时，图像就会因拉伸而失真。

为了让 ImageBrush 保持其图像的长宽比，请将 Stretch 属性设置为 Uniform 或 UniformToFill。

示例

下面的示例使用两个 ImageBrush 对象来绘制两个矩形。每个矩形都为 300x150 像素，每个矩形都包含一个 300x 300 像素的图像。第一个画笔的 Stretch 属性设置为 Uniform，第二个画笔的 Stretch 属性设置为 UniformToFill。

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

namespace Microsoft.Samples.Graphics.UsingImageBrush
{
    /// <summary>
    /// Demonstrates different ImageBrush Stretch settings.
    /// </summary>
    public class StretchModes : Page
    {
        public StretchModes()
        {

            // Create an ImageBrush with its Stretch
            // property set to Uniform. The image it
            // contains will be expanded as much as possible
            // to fill the output area while still
            // preserving its aspect ratio.
            ImageBrush uniformBrush = new ImageBrush();
            uniformBrush.ImageSource = 
                new BitmapImage(new Uri("sampleImages\\square.jpg", UriKind.Relative));
            uniformBrush.Stretch = Stretch.Uniform;

            // Freeze the brush (make it unmodifiable) for performance benefits.
            uniformBrush.Freeze();

            // Create a rectangle and paint it with the ImageBrush.
            Rectangle rectangle1 = new Rectangle();
            rectangle1.Width = 300;
            rectangle1.Height = 150;
            rectangle1.Stroke = Brushes.MediumBlue;
            rectangle1.StrokeThickness = 1.0;
            rectangle1.Fill = uniformBrush;

            // Create an ImageBrush with its Stretch
            // property set to UniformToFill. The image it
            // contains will be expanded to completely fill
            // the rectangle, but its aspect ratio is preserved.
            ImageBrush uniformToFillBrush = new ImageBrush();
            uniformToFillBrush.ImageSource =
                new BitmapImage(new Uri("sampleImages\\square.jpg", UriKind.Relative));
            uniformToFillBrush.Stretch = Stretch.UniformToFill;

            // Freeze the brush (make it unmodifiable) for performance benefits.
            uniformToFillBrush.Freeze();

            // Create a rectangle and paint it with the ImageBrush.
            Rectangle rectangle2 = new Rectangle();
            rectangle2.Width = 300;
            rectangle2.Height = 150;
            rectangle2.Stroke = Brushes.MediumBlue;
            rectangle2.StrokeThickness = 1.0;
            rectangle2.Margin = new Thickness(0, 10, 0, 0);
            rectangle2.Fill = uniformToFillBrush;

            StackPanel mainPanel = new StackPanel();
            mainPanel.Children.Add(rectangle1);
            mainPanel.Children.Add(rectangle2);

            Content = mainPanel;
            Background = Brushes.White;
            Margin = new Thickness(20);
            Title = "ImageBrush Stretch Modes";


        }
    }
}

<!-- Demonstrates different ImageBrush Stretch settings.-->
<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"
  Background="White" Margin="20"
  Title="ImageBrush Stretch Modes">
  <StackPanel>

    <!-- The ImageBrush in this example has its
         Stretch property set to Uniform. As a result,
         the image it contains is expanded as much as possible
         to fill the rectangle while
         still preserving its aspect ratio.-->
    <Rectangle
      Width="300" Height="150" 
      Stroke="MediumBlue" StrokeThickness="1">
      <Rectangle.Fill>
        <ImageBrush
          Stretch="Uniform" ImageSource="sampleImages\square.jpg"
          PresentationOptions:Freeze="True" />
      </Rectangle.Fill>
    </Rectangle>

    <!-- The ImageBrush in this example has its
         Stretch property set to UniformToFill. As a result,
         the image is expanded to completely fill
         the rectangle, but its aspect ratio is preserved.-->
    <Rectangle
      Width="300" Height="150"
      Stroke="MediumBlue" StrokeThickness="1"
      Margin="0,10,0,0">
      <Rectangle.Fill>
        <ImageBrush 
          Stretch="UniformToFill" ImageSource="sampleImages\square.jpg" 
          PresentationOptions:Freeze="True" />
      </Rectangle.Fill>
    </Rectangle>
  </StackPanel>
</Page>

下面的插图显示第一个画笔的输出，该画笔的 Stretch 设置为 Uniform。

下一个插图显示第二个画笔的输出，该画笔的 Stretch 设置为 UniformToFill。

请注意，Stretch 属性对于其他 TileBrush 对象（即，DrawingBrush 和 VisualBrush）的行为方式相同。有关 ImageBrush 和其他 TileBrush 对象的更多信息，请参见使用图像、绘图和 Visual 进行绘制。

另请注意，尽管 Stretch 属性似乎指定 TileBrush 内容如何拉伸以适合其输出区域，但是它实际上指定 TileBrush 内容如何拉伸以填充其基本平铺图像。有关更多信息，请参见 TileBrush。

此代码示例摘自一个为 ImageBrush 类提供的更大的示例。有关完整示例，请参见 ImageBrush 示例。

请参见

概念

使用图像、绘图和 Visual 进行绘制

参考

TileBrush