Rectangle Annotation With Rounded Corner in Oxyplot

It has been few months since I started playing around with Oxyplot, and it continues to impresses me. Having said that, there are times when certain challenges are thrown showing light on certain limitation of the tool. One of such limitation and a way to overcome is being discussed in this blog post.

Oxyplot supports a wide range of Annotations including Rectangle Annotation, Text Annotation, Image Annotation, Ellipse Annotation and Line Annotation among others. These by itself are extremely powerful and easy to use. However, recently I came across a business need where I would need to draw a Rectangle Annotation with Rounded Corner.

The Oxyplot library doesn’t allow us an in-build mechanism to do it. However, the good part is, that is not end of the road. We can create our own custom annotation. Before we hit code, it would be a good idea to discuss how we plan to create a RoundedCornerRectangleAnnotation.

Rounded Rectangle OxyPlot

The crux of the idea is to generate the rounded effect by drawing a set of two rectangle and 4 circle/ellipse. The Radius of the circles would be the intended corner radius of the final rectangle.

Okay, that’s enough for idea, let’s go ahead and write some code.

Part of Custom Annotation Class

 private void DrawRoundedRectangle(IRenderContext rc)
        {
            var xMin = double.IsNaN(this.MinimumX) || this.MinimumX.Equals(double.MinValue)
                            ? this.ClipByXAxis
                                ? this.XAxis.ActualMinimum
                                : this.XAxis.InverseTransform(this.PlotModel.PlotArea.Left)
                            : this.MinimumX;
            var xMax = double.IsNaN(this.MaximumX) || this.MaximumX.Equals(double.MaxValue)
                            ? this.ClipByXAxis
                                ? this.XAxis.ActualMaximum
                                : this.XAxis.InverseTransform(this.PlotModel.PlotArea.Right)
                            : this.MaximumX;
            var yMin = double.IsNaN(this.MinimumY) || this.MinimumY.Equals(double.MinValue)
                            ? this.ClipByYAxis
                                ? this.YAxis.ActualMinimum
                                : this.YAxis.InverseTransform(this.PlotModel.PlotArea.Bottom)
                            : this.MinimumY;
            var yMax = double.IsNaN(this.MaximumY) || this.MaximumY.Equals(double.MaxValue)
                            ? this.ClipByYAxis
                                ? this.YAxis.ActualMaximum
                                : this.YAxis.InverseTransform(this.PlotModel.PlotArea.Top)
                            : this.MaximumY;
            var xCornerRadius = (CornerRadius / (XAxis.Maximum - XAxis.Minimum)) * 100;
            var yCornerRadius = (CornerRadius / (YAxis.Maximum - YAxis.Minimum)) * 100;
            this.screenRectangleWithClippedXAxis = new OxyRect(this.Transform(xMin + xCornerRadius, yMin), this.Transform(xMax - xCornerRadius, yMax));
            this.screenRectangleWithClippedYAxis = new OxyRect(this.Transform(xMin, yMin + yCornerRadius), this.Transform(xMax, yMax - yCornerRadius));
            this.screenEllipseLeftBottom = new OxyRect(this.Transform(xMin, yMin), this.Transform(xMin + 2* xCornerRadius, yMin + 2* yCornerRadius));
            this.screenEllipseLeftTop = new OxyRect(this.Transform(xMin, yMax), this.Transform(xMin + 2 * xCornerRadius, yMax - 2 * yCornerRadius));
            this.screenEllipseRightBottom = new OxyRect(this.Transform(xMax, yMin), this.Transform(xMax - 2 * xCornerRadius, yMin + 2 * yCornerRadius));
            this.screenEllipseRightTop = new OxyRect(this.Transform(xMax, yMax), this.Transform(xMax - 2 * xCornerRadius, yMax - 2 * yCornerRadius));
            // clip to the area defined by the axes
            var clippingRectangle = OxyRect.Create(
                this.ClipByXAxis ? this.XAxis.ScreenMin.X : this.PlotModel.PlotArea.Left,
                this.ClipByYAxis ? this.YAxis.ScreenMin.Y : this.PlotModel.PlotArea.Top,
                this.ClipByXAxis ? this.XAxis.ScreenMax.X : this.PlotModel.PlotArea.Right,
                this.ClipByYAxis ? this.YAxis.ScreenMax.Y : this.PlotModel.PlotArea.Bottom);
            rc.DrawClippedRectangle(clippingRectangle,this.screenRectangleWithClippedXAxis,
                                            this.GetSelectableFillColor(this.Fill),
                                            this.GetSelectableColor(this.Stroke),
                                            this.StrokeThickness);
            rc.DrawClippedRectangle(clippingRectangle, this.screenRectangleWithClippedYAxis,
                                            this.GetSelectableFillColor(this.Fill),
                                            this.GetSelectableColor(this.Stroke),
                                            this.StrokeThickness);
            rc.DrawClippedEllipse(clippingRectangle, screenEllipseLeftBottom,
                                            this.GetSelectableFillColor(this.Fill),
                                            this.GetSelectableColor(this.Stroke),
                                            this.StrokeThickness);
            rc.DrawClippedEllipse(clippingRectangle, screenEllipseLeftTop,
                                this.GetSelectableFillColor(this.Fill),
                                this.GetSelectableColor(this.Stroke),
                                this.StrokeThickness);
            rc.DrawClippedEllipse(clippingRectangle, screenEllipseRightBottom,
                                this.GetSelectableFillColor(this.Fill),
                                this.GetSelectableColor(this.Stroke),
                                this.StrokeThickness);
            rc.DrawClippedEllipse(clippingRectangle, screenEllipseRightTop,
                                this.GetSelectableFillColor(this.Fill),
                                this.GetSelectableColor(this.Stroke),
                                this.StrokeThickness);
            if (!string.IsNullOrEmpty(this.Text))
            {
                var textPosition = this.GetActualTextPosition(() => this.screenRectangle.Center);
                rc.DrawClippedText(
                    clippingRectangle,
                    textPosition,
                    this.Text,
                    this.ActualTextColor,
                    this.ActualFont,
                    this.ActualFontSize,
                    this.ActualFontWeight,
                    this.TextRotation,
                    HorizontalAlignment.Center,
                    VerticalAlignment.Middle);
            }
        }

 

You can find the complete class code in Gist Link. The complete source code, including the WPF Wrapper can be found in the forked implementation at my GitHub.

PS:The implementation, of course has its own flaws. You cannot set Stroke for the Rounded Rectangle, hopefully, I would be able to workaround this issue soon.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s