使用RenderTargetBitmap创建WPF Canvas区域的快照

Question

我想在我的应用程序中创建一个Canvas区域的快照.我正在使用Visual Brush来获取快照并使用PngEncoder保存它.但是生成的PNG只是一个空白的黑色图像.我不确定问题是创建的BitmapSource还是PNGEncoder问题.这是我用来获取相同代码的代码.

public void ConvertToBitmapSource(UIElement element)
{
    var target = new RenderTargetBitmap((int)(element.RenderSize.Width), (int)(element.RenderSize.Height), 96, 96, PixelFormats.Pbgra32);
    var brush = new VisualBrush(element);

    var visual = new DrawingVisual();
    var drawingContext = visual.RenderOpen();


    drawingContext.DrawRectangle(brush, null, new Rect(new Point(0, 0),
    new Point(element.RenderSize.Width, element.RenderSize.Height)));

    drawingContext.Close();

    target.Render(visual);

    PngBitmapEncoder encoder = new PngBitmapEncoder();
    BitmapFrame outputFrame = BitmapFrame.Create(target);
    encoder.Frames.Add(outputFrame);
    using (FileStream file = File.OpenWrite("TestImage.png"))
    {
         encoder.Save(file);
    }

}   

Answer 1

谢谢你们的问题和答案.

为了其他人的利益寻找相同的答案

我发现Clemens方式在图像中留下了黑带,图像向下或向右移动.好像它没有将元素渲染到位图中的正确位置.

所以我不得不像Amar建议的那样使用VisualBrush.

这是适合我的代码:

    RenderTargetBitmap RenderVisual(UIElement elt)
    {
        PresentationSource source = PresentationSource.FromVisual(elt);
        RenderTargetBitmap rtb = new RenderTargetBitmap((int)elt.RenderSize.Width,   
              (int)elt.RenderSize.Height, 96, 96, PixelFormats.Default);

        VisualBrush sourceBrush = new VisualBrush(elt);
        DrawingVisual drawingVisual = new DrawingVisual();
        DrawingContext drawingContext = drawingVisual.RenderOpen();
        using (drawingContext)
        {
            drawingContext.DrawRectangle(sourceBrush, null, new Rect(new Point(0, 0), 
                  new Point(elt.RenderSize.Width, elt.RenderSize.Height)));
        }
        rtb.Render(drawingVisual);

        return rtb;
    }

Answer 2

不确定为什么你的代码无法正常工作.这有效:

public void WriteToPng(UIElement element, string filename)
{
    var rect = new Rect(element.RenderSize);
    var visual = new DrawingVisual();

    using (var dc = visual.RenderOpen())
    {
        dc.DrawRectangle(new VisualBrush(element), null, rect);
    }

    var bitmap = new RenderTargetBitmap(
        (int)rect.Width, (int)rect.Height, 96, 96, PixelFormats.Default);
    bitmap.Render(visual);

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

    using (var file = File.OpenWrite(filename))
    {
        encoder.Save(file);
    }
}