Convert DrawingContext to Geometry?

Question

Does anybody know whether there is a possiblity to save or convert a DrawingContext to a Geometry?

E.g. after

using (DrawingContext dc = RenderOpen())
{
    dc.DrawLine(penSelected, Data.MidTop, Data.MidTop + vertical);
    dc.DrawLine(pen, Data.MidTop - horizontal, Data.MidTop + thickness);
    dc.DrawLine(pen, Data.MidTop + vertical - thickness, Data.MidTop + horizontal + vertical);
    dc.DrawText(new FormattedText(Data.Time2.ToString("0.0"), cultureinfo, FlowDirection.LeftToRight, typeface, 8, Brushes.Black),
        Data.MidTop + 3 * thickness);
    dc.DrawText(new FormattedText(Data.Time2.ToString("0.0"), cultureinfo, FlowDirection.LeftToRight, typeface, 8, Brushes.Black),
        Data.MidTop + vertical - horizontal - 3 * thickness);
}

to somehow save the drawn objects in a geometry?

Answer 1

When you populate a DrawingVisual with visual content, you are effectively creating a hierarchical collection of Drawing objects, which are accessible by the DrawingVisual's Drawing property (of type DrawingGroup). Each of these Drawing objects is actually of one of the following types:

• GeometryDrawing
• GlyphRunDrawing
• ImageDrawing
• VideoDrawing
• DrawingGroup

Two of these provide a property or method to get a Geometry. Obviously, GeometryDrawing has a Geometry property, whereas GlyphRunDrawing has a GlyphRun property that returns a GlyphRun object, which in turn has a BuildGeometry method. This method returns a Geometry of the outline of the GlyphRun's text.

A static helper method to create a Geometry from a DrawingGroup may look like this:

public static Geometry CreateGeometry(DrawingGroup drawingGroup)
{
    var geometry = new GeometryGroup();

    foreach (var drawing in drawingGroup.Children)
    {
        if (drawing is GeometryDrawing)
        {
            geometry.Children.Add(((GeometryDrawing)drawing).Geometry);
        }
        else if (drawing is GlyphRunDrawing)
        {
            geometry.Children.Add(((GlyphRunDrawing)drawing).GlyphRun.BuildGeometry());
        }
        else if (drawing is DrawingGroup)
        {
            geometry.Children.Add(CreateGeometry((DrawingGroup)drawing));
        }
    }

    geometry.Transform = drawingGroup.Transform;
    return geometry;
}

You would just pass the value of the DrawingVisual's Drawing property to this method:

var geometry = CreateGeometry(visual.Drawing);