Question

我正在关注this文章，我得到了保存的画布，但是，我想扩展代码的功能并将画布的特定部分保存为图像，而不是整个画布。

我尝试设置rect.Offset和rect.Location属性，但图片始终保存在画布的左上角。

有谁知道如何以类似的方式实现我想要的功能？

谢谢！

Answer 1

一种简单的方法是在渲染整个画布后使用CroppedBitmap。如果需要多个图像，可以重复使用相同的RenderTargetBitmap。

RenderTargetBitmap rtb = new RenderTargetBitmap((int)canvas.RenderSize.Width,
    (int)canvas.RenderSize.Height, 96d, 96d, System.Windows.Media.PixelFormats.Default);
rtb.Render(canvas);

var crop = new CroppedBitmap(rtb, new Int32Rect(50, 50, 250, 250));

BitmapEncoder pngEncoder = new PngBitmapEncoder();
pngEncoder.Frames.Add(BitmapFrame.Create(crop));

using(var fs = System.IO.File.OpenWrite("logo.png"))
{
    pngEncoder.Save(fs);
}

Answer 2

我知道这是一个古老的问题，但是我花了一些时间搜索并尝试不同的答案才能得出可靠可靠的结果。因此，为将来节省一些时间，这里提供了一项小服务，可以将画布保存到文件中，或者返回ImageSource以便在应用程序中的其他位置显示。

对于生产应用程序，附加的空值和错误检查等，应使其更加健壮。

public static class RenderVisualService
{
    private const double defaultDpi = 96.0;

    public static ImageSource RenderToPNGImageSource(Visual targetControl)
    {
        var renderTargetBitmap = GetRenderTargetBitmapFromControl(targetControl);

        var encoder = new PngBitmapEncoder();
        encoder.Frames.Add(BitmapFrame.Create(renderTargetBitmap));

        var result = new BitmapImage();

        using (var memoryStream = new MemoryStream())
        {
            encoder.Save(memoryStream);
            memoryStream.Seek(0, SeekOrigin.Begin);

            result.BeginInit();
            result.CacheOption = BitmapCacheOption.OnLoad;
            result.StreamSource = memoryStream;
            result.EndInit();
        }

        return result;
    }

    public static void RenderToPNGFile(Visual targetControl, string filename)
    {
        var renderTargetBitmap = GetRenderTargetBitmapFromControl(targetControl);

        var encoder = new PngBitmapEncoder();
        encoder.Frames.Add(BitmapFrame.Create(renderTargetBitmap));

        var result = new BitmapImage();

        try
        {
            using (var fileStream = new FileStream(filename, FileMode.Create))
            {
                encoder.Save(fileStream);
            }
        }
        catch (Exception ex)
        {
            System.Diagnostics.Debug.WriteLine($"There was an error saving the file: {ex.Message}");
        }
    }

    private static BitmapSource GetRenderTargetBitmapFromControl(Visual targetControl, double dpi = defaultDpi)
    {
        if (targetControl == null) return null;

        var bounds = VisualTreeHelper.GetDescendantBounds(targetControl);
        var renderTargetBitmap = new RenderTargetBitmap((int)(bounds.Width * dpi / 96.0),
                                                        (int)(bounds.Height * dpi / 96.0),
                                                        dpi,
                                                        dpi,
                                                        PixelFormats.Pbgra32);

        var drawingVisual = new DrawingVisual();

        using (var drawingContext = drawingVisual.RenderOpen())
        {
            var visualBrush = new VisualBrush(targetControl);
            drawingContext.DrawRectangle(visualBrush, null, new Rect(new Point(), bounds.Size));
        }

        renderTargetBitmap.Render(drawingVisual);
        return renderTargetBitmap;
    }
}

还有一个示例WPF应用程序演示了它的使用。

MainWindow.xaml

<Window x:Class="CanvasToBitmapDemo.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:CanvasToBitmapDemo"
    mc:Ignorable="d"
    Title="MainWindow" Height="450" Width="800">
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="Auto" />
        <RowDefinition Height="Auto" />
    </Grid.RowDefinitions>

    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
    </Grid.ColumnDefinitions>

    <StackPanel Grid.Row="0" Grid.ColumnSpan="2" Orientation="Horizontal" HorizontalAlignment="Center">
        <Button Click="Button_Click" Content="Capture Image" Width="100"/>
        <Button Click="Button_Click_1" Content="Save To Disk" Width="100"/>
    </StackPanel>

    <Canvas x:Name="PART_Canvas" Grid.Row="1" Grid.Column="0">
        <Ellipse Canvas.Top="50"
                 Canvas.Left="60"
                 Fill="Gold"
                 Width="250"
                 Height="250" />

        <Polyline Stroke="#FF853D00"
                  StrokeThickness="10"
                  StrokeEndLineCap="Round"
                  StrokeStartLineCap="Round"
                  Points="110,100 120,97 130,95 140,94 150,95 160,97 170,100" />

        <Ellipse Canvas.Top="115"
                 Canvas.Left="114"
                 Fill="#FF853D00"
                 Width="45"
                 Height="50" />

        <Polyline Stroke="#FF853D00"
                  StrokeThickness="10"
                  StrokeEndLineCap="Round"
                  StrokeStartLineCap="Round"
                  Points="205,120 215,117 225,115 235,114 245,115 255,117 265,120" />

        <Ellipse Canvas.Top="120"
                 Canvas.Left="208"
                 Fill="#FF853D00"
                 Width="45"
                 Height="50" />

        <Polyline Stroke="#FF853D00"
                  StrokeThickness="10"
                  StrokeEndLineCap="Round"
                  StrokeStartLineCap="Round"
                  Points="150,220 160,216 170,215 180,215 190,216 202,218 215,221" />

    </Canvas>

    <Image x:Name="PART_Image" Grid.Row="1" Grid.Column="1" Stretch="None"/>
</Grid>

以及调用服务的背后代码。

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        PART_Image.Source = RenderVisualService.RenderToPNGImageSource(PART_Canvas);
    }

    private void Button_Click_1(object sender, RoutedEventArgs e)
    {
        RenderVisualService.RenderToPNGFile(PART_Canvas, "myawesomeimage.png");
    }
}

Answer 3

查看此解决方案是否适合您。

Size size = new Size(width, height);
canvas.Measure(size);
canvas.Arrange(new Rect(X, Y, width, height));

//Save Image
...  
...

// Revert old position
canvas.Measure(new Size());

Answer 4

查看您发布的链接，显然您可以在此处选择渲染的目标坐标。

RenderTargetBitmap rtb = new RenderTargetBitmap((int)rect.Right,
     (int)rect.Bottom, 96d, 96d, System.Windows.Media.PixelFormats.Default);

将WPF画布保存为图像

4 个答案: