#1,151 – Custom Arc Shape, part III

In the previous example of a custom arc shape, we use the standard Stroke and StrokeThickness properties when rendering the shape.  Note, however, that when we increase the thickness of the stroke, part of the stroke lies outside of the boundaries of the shape.

We can fix this problem by accounting for the stroke thickness in the drawing logic.  The updated code is shown below.

        protected override Geometry DefiningGeometry
        {
            get
            {
                double maxWidth = Math.Max(0.0, RenderSize.Width - StrokeThickness);
                double maxHeight = Math.Max(0.0, RenderSize.Height - StrokeThickness);
                //Console.WriteLine(string.Format("* maxWidth={0}, maxHeight={1}", maxWidth, maxHeight));

                double xStart = maxWidth / 2.0 * Math.Cos(StartAngle * Math.PI / 180.0);
                double yStart = maxHeight / 2.0 * Math.Sin(StartAngle * Math.PI / 180.0);

                double xEnd = maxWidth / 2.0 * Math.Cos(EndAngle * Math.PI / 180.0);
                double yEnd = maxHeight / 2.0 * Math.Sin(EndAngle * Math.PI / 180.0);

                StreamGeometry geom = new StreamGeometry();
                using (StreamGeometryContext ctx = geom.Open())
                {
                    ctx.BeginFigure(
                        new Point((RenderSize.Width / 2.0) + xStart,
                                  (RenderSize.Height / 2.0) - yStart),
                        false,
                        false);
                    ctx.ArcTo(
                        new Point((RenderSize.Width / 2.0) + xEnd,
                                  (RenderSize.Height / 2.0) - yEnd),
                        new Size(maxWidth / 2.0, maxHeight / 2),
                        0.0,     // rotationAngle
                        (EndAngle - StartAngle) > 180,   // greater than 180 deg?
                        SweepDirection.Counterclockwise,
                        true,    // isStroked
                        true);
                }

                return geom;
            }
        }