Getting a DrawingContext for a wpf WriteableBitmap

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I found sixlettervariables’ solution the most workable one. However, there’s a “drawingContext.Close()” missing. According to MSDN, “A DrawingContext must be closed before its content can be rendered”.
The result is the following utility function:

public static BitmapSource CreateBitmap(
    int width, int height, double dpi, Action<DrawingContext> render)
{
    DrawingVisual drawingVisual = new DrawingVisual();
    using (DrawingContext drawingContext = drawingVisual.RenderOpen())
    {
        render(drawingContext);
    }
    RenderTargetBitmap bitmap = new RenderTargetBitmap(
        width, height, dpi, dpi, PixelFormats.Default);
    bitmap.Render(drawingVisual);

    return bitmap;
}

This can then easily be used like this:

BitmapSource image = ImageTools.CreateBitmap(
    320, 240, 96,
    drawingContext =>
    {
        drawingContext.DrawRectangle(
            Brushes.Green, null, new Rect(50, 50, 200, 100));
        drawingContext.DrawLine(
            new Pen(Brushes.White, 2), new Point(0, 0), new Point(320, 240));
    });

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