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Editorial Team
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Asked: 2026-05-28T14:01:51+00:00

I was trying to create a brush that draws a geometry. Everything worked fine

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I was trying to create a brush that draws a geometry. Everything worked fine until I tried to add Dashing to the shape.

I found that when I create the geometry using Geometry.Parse, the dashed line appears correctly, but when I create it directly using StreamGeometryContext, nothing gets rendered.

This is the code I’m using:

private void RenderGeometryAndSetAsBackground()
{
    Point startPoint = new Point(3505961.52400725, 3281436.57325874);
    Point[] points = new Point[] {
        new Point(3503831.75515445,3278705.9649394),
        new Point(3503905.74802898,3278449.37713916),
        new Point(3507242.57331039,3276518.41148474),
        new Point(3507700.6914325,3276536.23547958),
        new Point(3510146.73449577,3277964.12812859),
        new Point(3509498.96473447,3278678.60178448),
        new Point(3507412.1889951,3277215.64022219),
        new Point(3504326.22698001,3278682.85514017),
        new Point(3506053.34789057,3281390.66371786)};

    string geom = "M3505961.52400725,3281436.57325874L3503831.75515445,3278705.9649394 3503905.74802898,3278449.37713916 3507242.57331039,3276518.41148474 3507700.6914325,3276536.23547958 3510146.73449577,3277964.12812859 3509498.96473447,3278678.60178448 3507412.1889951,3277215.64022219 3504326.22698001,3278682.85514017 3506053.34789057,3281390.66371786";
    //Geometry geometry = StreamGeometry.Parse(geom);

    StreamGeometry geometry = new StreamGeometry();
    using (StreamGeometryContext sgc = geometry.Open())
    {
        sgc.BeginFigure(startPoint, false, true);
        foreach (Point p in points)
        {
            sgc.LineTo(p, true, true);
        }
    }

    Pen pen = new Pen(Brushes.Yellow, 3);
    pen.DashStyle = new DashStyle(new double[] { 30, 30 }, 0);
    //GeometryDrawing gd = new GeometryDrawing(null, pen, path.RenderedGeometry);
    GeometryDrawing gd = new GeometryDrawing(null, pen, geometry);
    DrawingBrush drawingBrush = new DrawingBrush(gd);
    DrawingBrush tile = drawingBrush.Clone();
    tile.Viewbox = new Rect(0.5, 0, 0.25, 0.25);
    RenderTargetBitmap rtb = new RenderTargetBitmap(256, 256, 96, 96, PixelFormats.Pbgra32);

    var drawingVisual = new DrawingVisual();
    using (DrawingContext context = drawingVisual.RenderOpen())
    {
        context.DrawRectangle(tile, null, new Rect(0, 0, 256, 256));
    }
    rtb.Render(drawingVisual);

    ImageBrush bgBrush = new ImageBrush(rtb);
    Background = bgBrush;
}

When done that way, nothing is getting drawn. If I don’t use dashing (or set the dashing to null) it works fine. It also works if I use the StreamGeometry.Parse(geom) and keeps the dashing.

Trying to call sgc.Close() didn’t help. Currently my only workaround is to call:

geometry = Geometry.Parse(geometry.ToString());

which is not very nice…

What am I missing?

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1 Answer

  1. Editorial Team

    That’s a pretty fascinating bug you got there, I can confirm it. Some ILSpy digging revealed the cause: the implicit BeginFigure call that is generated by Geometry.Parse sets the isFilled parameter to true, whereas you set it to false in your explicit StreamGeometryContext call. Change the second parameter in sgc.BeginFigure from false to true, and the dashed lines will render.

    The WPF path markup syntax does not allow specifying whether any individual figure should be filled or not, so I suppose that’s why the parser defaults to filling them all, just to be sure. But I can’t see any good reason why dashed lines would require filled figures, that has to be a WPF bug.

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