LineCap, DashCap, and DashStyle in GDI+

This article has been excerpted from book "Graphics Programming with GDI+".

Pens offer more options than what we have seen so far. A line's caps are the starting and ending points of the line. For example, you may have seen lines with arrows and circles. Figure 4.24 shows some lines with their cap and dash styles.

Using Pen properties and methods, you can draw lines with cap and dash styles. Here we will discuss line cap and line dash styles only briefly.

Note: We can divide caps into two types: anchor and nonanchor. The width of an anchor cap is bigger than the width of the line; the width of a nonanchor cap is the same as the width of the line.

The LineCap property of the Pen class represents the cap style used at the beginning and ending of lines drawn by the pen. You can determine the current cap style of a line by calling the GetLineCap method, which returns a LineCap enumeration. You can also apply a line cap style using the SetLineCap method. This method takes an argument of LineCap enumeration type. Table 4.12 describes the members of the LineCap enumeration.

The SetLineCap method takes the line cap style for the beginning, ending, and dash cap of the line. The first and second parameters of SetLineCap are of type LineCap. The third parameter is of type DashCap enumeration



FIGURE 4.24: Line cap and dash styles

TABLE 4.12: LineCap members

Member	Description
AnchorMask	A mask used to check whether a line cap is an anchor cap.
ArrowAnchor	An arrow-shaped anchor cap.
Custom	A custom line cap.
DiamondAnchor	A diamond anchor cap.
Flat	A flat line cap.
NoAnchor	No anchor.
Round	A round line cap.
RoundAnchor	A round anchor cap.
Square	A square line cap.
SquareAnchor	A square anchor cap.
Triangle	A triangular line cap.

TABLE 4.13: DashCap members

Member	Description
Flat	A square cap that squares off both ends of each dash.
Round	A circular cap.
Triangle	A triangular cap.

The DashCap enumeration specifies the type of graphics shapes used on both ends of each dash in a dashed line. Table 4.13 describes the members of the DashCap enumeration.

The DashStyle enumeration specifies the style of a dashed line drawn by the pen. Table 4.14 describes the members of the DashStyle enumeration.

TABLE 4.14: DashStyle members

Member	Description
Custom	A user-defined custom dash style.
Dash	A line consisting of dashes.
DashDot	A line consisting of a repeating dash-dot pattern.
DashDotDot	A line consisting of a repeating dash-dot pattern of.
Dot	A line consisting of dots.
Solid	A solid line.

Listing 4.20 shows how to use various styles and properties of the Pen class to draw different kinds of dashed lines with different kinds of starting and ending caps. We use the DashStyle, SetLineCap, StartCap, and EndCap members of the Pen class to set the line dash style, line cap style, start cap style, and end cap style, respectively.

LISTING 4.20: Using the Pen class to draw dashed lines

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace LineCapDash
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = this.CreateGraphics();
            g.Clear(this.BackColor);

            //Create three pens
            Pen redPen = new Pen(Color.Red, 6);
            Pen bluePen = new Pen(Color.Blue, 7);
            Pen greenPen = new Pen(Color.Green, 7);
            redPen.Width = 8;

            //Set line styles
            redPen.DashStyle = DashStyle.Dash;
            redPen.SetLineCap(LineCap.DiamondAnchor,
            LineCap.ArrowAnchor, DashCap.Flat);
            greenPen.DashStyle = DashStyle.DashDotDot;
            greenPen.StartCap = LineCap.Triangle;
            greenPen.EndCap = LineCap.Triangle;
            greenPen.DashCap = DashCap.Triangle;
            greenPen.DashStyle = DashStyle.Dot;
            greenPen.DashOffset = 3.4F;
            bluePen.StartCap = LineCap.DiamondAnchor;
            bluePen.EndCap = LineCap.DiamondAnchor;
            greenPen.SetLineCap(LineCap.RoundAnchor,
                LineCap.Square, DashCap.Round);

            //Draw lines
            g.DrawLine(redPen, new Point(20, 50),
                new Point(150, 50));
            g.DrawLine(greenPen, new Point(30, 80),
                new Point(200, 80));
            g.DrawLine(bluePen, new Point(30, 120),
                new Point(250, 120));

            //Release resources. If you don't release
            //using Dispose, the GC (garbage collector)
            //takes care of it for you.
            redPen.Dispose();
            greenPen.Dispose();
            g.Dispose();
        }
    }
}

Figure 4.25 shows the output from Listing 4.20.


FIGURE 4.25: Drawing dashed lines with different cap style

Conclusion

Hope the article would have helped you in understanding LineCap, DashCap, and DashStyle in GDI+. Read other articles on GDI+ on the website.

This book teaches .NET developers how to work with GDI+ as they develop applications that include graphics, or that interact with monitors or printers. It begins by explaining the difference between GDI and GDI+, and covering the basic concepts of graphics programming in Windows.