Question

我正试图在我的应用拍摄的照片上添加水印。我能想到的最简单的方法是使用FrameworkElement构建图层，然后使用RenderTargetBitmap创建水印图像。

以下是我的XAML示例。

    <ScrollViewer x:Name="Zoom" Grid.Column="1" HorizontalScrollMode="Enabled" VerticalScrollMode="Enabled" VerticalScrollBarVisibility="Hidden" HorizontalScrollBarVisibility="Hidden" ZoomMode="Enabled">
        <Border x:Name="BgBorder">
            <Grid x:Name="ImageGird" SizeChanged="ImageGird_SizeChanged">
                <Grid x:Name="CaptureGird">
                    <Image x:Name="CapturedImage" Stretch="None" Source="ms-appx:///Assets/Photo.jpg" />
                    <StackPanel x:Name="Watermark" VerticalAlignment="Top" HorizontalAlignment="Left" Background="#6FFFFFFF" Margin="10">
                        <TextBlock Text="Name" Foreground="Black" Margin="10,2.5,10,2.5" />
                        <TextBlock Text="12345" Foreground="Black" Margin="10,2.5,10,2.5"/>
                        <TextBlock Text="54321" Foreground="Black" Margin="10,2.5,10,2.5" />
                    </StackPanel>
                </Grid>
            </Grid>
        </Border>
    </ScrollViewer>

由于所需图像的分辨率，它被包裹在ScrollViewer中，因此可以缩小，但是当我尝试使用下面的代码创建此图像的位图时，渲染的位图比较小FrameworkElement

private async void Button_Click(object sender, RoutedEventArgs e)
{
    try
    {
        var displayI = DisplayInformation.GetForCurrentView();
        var renderTargetBitmap = new RenderTargetBitmap();
        await renderTargetBitmap.RenderAsync(ImageGird, (int)ImageGird.ActualWidth, (int)ImageGird.ActualHeight);
        IBuffer pixels = await renderTargetBitmap.GetPixelsAsync();
        CapturedImage2.Source = renderTargetBitmap;

        Debug.WriteLine("Button_Click: ImageGrid: " + ImageGird.ActualWidth + "x" + ImageGird.ActualHeight + " RenderTargetBitmap: " + renderTargetBitmap.PixelWidth + "x" + renderTargetBitmap.PixelHeight);
    }
    catch (Exception )
    {
    }
}

调试输出

Button_Click: ImageGrid: 5344x3008 RenderTargetBitmap: 4096x2306

有人能告诉我为什么渲染的位图比我创建它的实际元素要小得多吗？

还有更好的方法为图像添加水印吗？

Answer 1

ActualWidth和ActualHeight是计算值。因此，特别是对于网格而言，这些值可能会随着时间的推移而改变。我的猜测是，当你设置图像源时，重新计算实际的宽度和高度。

我认为您应该能够使堆栈面板成为图像的子项并将其相对于父图像定位，这将使其适用于可变图像大小。您还可以尝试在网格上设置一些约束，并使用它们来确定您的位图大小，而不是使用实际的宽度/高度。

Answer 2

Havel a look Win2D并使用离屏绘图。

Answer 3

感谢@ A.J.Bauer向我指出Win2D，我能够非常优雅地解决这个问题。

    /// <summary>
    /// Create a watermarked image from an image stream
    /// </summary>
    /// <param name="sender">Jpeg image stream.</param>
    private async Task<ImageSource> CreateWaterMarkedImage(IRandomAccessStream stream)
    {
        // Ensure our stream is at the beginning.
        stream.Seek(0);
        // Create our Win2D in memory renderer.
        CanvasDevice device = CanvasDevice.GetSharedDevice();
        CanvasRenderTarget offscreen = new CanvasRenderTarget(device, (float)ImageGird.ActualWidth, (float)ImageGird.ActualHeight, 96);
        // Create our Win2D bitmap
        CanvasBitmap bmp = await CanvasBitmap.LoadAsync(offscreen, stream, 96);
        // Create a text formatter for our watermark
        var format = new CanvasTextFormat()
        {
            FontSize = 40,
            HorizontalAlignment = CanvasHorizontalAlignment.Left,
            VerticalAlignment = CanvasVerticalAlignment.Top,
            WordWrapping = CanvasWordWrapping.Wrap,
            FontFamily = "Arial",
            FontWeight = FontWeights.SemiBold
        };
        // Get a Win2D drawing session instance
        using (CanvasDrawingSession ds = offscreen.CreateDrawingSession())
        {
            // Layer our resulting Watermarked image.
            ds.DrawImage(bmp);
            // Create the Win2D text layout so we can get the bounds.
            var tl = new CanvasTextLayout(ds, "Name\r\n12345\r\n54321", format, 1000, 1000);
            // Create a background for the text
            ds.FillRectangle(10, 10, (float)tl.DrawBounds.Width + 20f, (float)tl.DrawBounds.Height + 20f, new Color() { A = 0x6F, R = 0xFF, G = 0xFF, B = 0xFF });
            // Add the text layout.
            ds.DrawTextLayout(tl, 10, 10, Colors.Black);
            // Clear up the memory.
            tl.Dispose();
        }

        // Create our bitmap so we can return an ImageSource
        BitmapImage im = new BitmapImage();
        using (InMemoryRandomAccessStream oStream = new InMemoryRandomAccessStream())
        {
            // Save the Win2D canvas renderer a stream.
            await offscreen.SaveAsync(oStream, CanvasBitmapFileFormat.Jpeg, 1.0f);
            stream.Seek(0);
            // Stream our Win2D pixels into the Bitmap
            await im.SetSourceAsync(oStream);
            Debug.WriteLine("CreateWaterMarkedImage: ImageGrid: " + ImageGird.ActualWidth + "x" + ImageGird.ActualHeight + " Bitmap: " + im.PixelWidth + "x" + im.PixelHeight);
        }
        // Tidy Up.
        format.Dispose();
        bmp.Dispose();
        offscreen.Dispose();
        device.Dispose();
        return im;
    }

结果调试给了我。

CreateWaterMarkedImage: ImageGrid: 5344x3008 Bitmap: 5344x3008

如果设置Image UIElement的来源，则会显示带水印的图像。

CapturedImage2.Source = await CreateWaterMarkedImage(photoStream);

此示例非常适合我的需求，但是如果您使用Win2D XAML控件，任何人都应该能够轻松地进行调整。

Windows应用商店应用 - RenderTargetBitmap创建不正确大小的位图

3 个答案: