DrawingGroup Vs DrawingVisual Transform

问题

I have two methods that draw a rotated rectangle on the screen.

RenderMethod1 renders a rectangle rotated by 30 degrees using a DrawingVisual

private static void RenderMethod1(DrawingContext dc) {
    DrawingVisual drawingVisual = new DrawingVisual();
    using (DrawingContext context = drawingVisual.RenderOpen()) {
        Rect rect = new Rect(new System.Windows.Point(100, 100), new System.Windows.Size(320, 80));
        context.DrawRectangle(System.Windows.Media.Brushes.LightBlue, (System.Windows.Media.Pen)null, rect);
    }
    drawingVisual.Transform = new RotateTransform(30, 100, 100);
    dc.DrawDrawing(drawingVisual.Drawing);
}

RenderMethod2 renders a rectangle rotated by 30 degrees using a DrawingGroup

    private static void RenderMethod2(DrawingContext dc) {
        DrawingGroup group = new DrawingGroup();
        DrawingVisual drawingVisual = new DrawingVisual();
        using (DrawingContext context = drawingVisual.RenderOpen()) {
            Rect rect = new Rect(new System.Windows.Point(100, 100), new System.Windows.Size(320, 80));
            context.DrawRectangle(System.Windows.Media.Brushes.LightBlue, (System.Windows.Media.Pen)null, rect);
        }
        group.Children.Add(drawingVisual.Drawing);
        group.Transform = new RotateTransform(30, 100, 100);
        group.Freeze();
        dc.DrawDrawing(group);
    }

The output is as follows:

RenderMethod1

RenderMethod2

As you can see RenderMethod1 and RenderMethod2 outputs are supposed to be exactly the same but they are not. Is there anything I am doing wrong in RenderMethod1?

Thanks for help in advance,

回答1:

I finally got around the problem by changing RenderMethod1 as follow and it works as expected.

private static void RenderMethod1(DrawingContext dc) {
    DrawingGroup drawingVisual = new DrawingGroup();
    using (DrawingContext context = drawingVisual.Open()) {
        Rect rect = new Rect(new System.Windows.Point(100, 100), new System.Windows.Size(320, 80));
        context.DrawRectangle(System.Windows.Media.Brushes.LightBlue, (System.Windows.Media.Pen)null, rect);
    }
    drawingVisual.Transform = new RotateTransform(30, 100, 100);
    dc.DrawDrawing(drawingVisual);
}

来源：https://stackoverflow.com/questions/8565002/drawinggroup-vs-drawingvisual-transform

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transform