System Pens and System Brushes in GDI+

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

System pens and system brushes are pens and brushes that are used to create system colors. In this section we will discuss how to create and use system pens and brushes.

There are two ways to create system pens and brushes. First, you can create pens and brushes using the SystemColors class. SystemColors represents the system colors in GDI+, providing static properties for system colors, such as ActiveBorder and ControlText. The second way to create systems pens and brushes use the SystemPens and SystemBrushes classes.

For performance reasons, it is a good idea to use the SystemPens and SystemBrushes classes rather than creating pens and brushes by using the SystemColors class.

System Pens

The SystemPens class represents a pen created with the system colors. This class has a static property for each system color that represents the system pen with that particular color. Table 4.16 lists the properties of the SystemPens class.

The SystemPens class also provides a method FormSystemColor that creates a Pen object from a Color structure. To create a system pen, we pass a SystemColors object. The following code shows how to use the FromSystemColor method:

            Pen pn = SystemPens.FromSystemColor(SystemColors.HotTrack);

TABLE 4.16: SystemPens properties

Property	Description
ActiveCaptionText	Pen with active window's title bar color
Control	Pen with control color
ControlDark	Pen with the shadow color of a 3D element
ControlDarkDark	Pen with the dark shadow color of a 3D element
ControlLight	Pen with the light color of a 3D element
ControlLightLight	Pen with the highlight color of a 3D element
ControlText	Pen with the control text color
GrayText	Pen with disabled color
Highlight	Pen with highlighting
HighlightText	Pen with highlighted text color
InactiveCaptionText	Pen with inactive title bar color
InfoText	Pen with the color of the text of a ToolTip
MenuText	Pen with the color of a menu's text
WindowFrame	Pen with the color of a window frame
WindowText	Pen with the color of the text in the client area of a window

System Brushes

The SystemBrushes class represents a Brush object using the system colors. All properties of SystemBrushes are static read-only properties. Table 4.17 describes these properties.

TABLE 4.17: SystemBrushes properties

Property	Description
ActiveBorder	Brush object with the color of the active window's border
ActiveCaption	Brush object with the background color of the active window's title bar
ActiveCaptionText	Brush object with the color of the text active window's title bar
AppWorkspace	Brush object with the color of the application work space
Control	Brush object with the face color of a 3D element
ControlDark	Brush object with the shadow color of a 3D element
ControlDarkDark	Brush object with the dark shadow color of a 3D element
ControlLight	Brush object with the light color of a 3D element
ControlLightLight	Brush object with the highlight color of a 3D element
ControlText	Brush object with the color of text in a 3D element
Desktop	Brush object with the color of the desktop
Highlight	Brush object with the color of the background of selected items
HighlightText	Brush object with the color of the text of selected items
HotTrack	Brush object with the color used to designate a hot tracked item
InactiveBorder	Brush object with the color of an inactive window's title bar
InactiveCaption	Brush object with the color of the background of an inactive window's title bar
Info	Brush object with the color of the background of a ToolTip
Menu	Brush object with the color of a menu's background
ScrollBar	Brush object with the color of the background of a scroll bar
Window	Brush object with the color of the background in the client area of a window
WindowText	Brush object with the color of the text in the client area of a window

Note: The MSDN documentation states that the SystemBrushes properties return a SolidBrush object, but that the statement is not quite accurate. These properties return a Brush object that must be cast to a SolidBrush object. If you run the code without casting them, the compiler throws an error.

The SystemBrushes class also provides a FromSystemColor method, which creates a Brush Object from a specified system color. The following code shows how to use the FromSystemMethod:

            SolidBrush brush = (SolidBrush)SystemBrushes.FromSystemColor(SystemColors.ActiveCaption);

Disposing of System Pens and Brushes

You cannot dispose of system pens and brushes. If you try to dispose of them, GDIF+ generates an error because these objects belong to the system

Listing 4.26 uses SystemBrushes and SystemPens object to draw two lines and rectangle.

Listing 4.26: Using the SystemBrushes and SystemPens classes

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;

namespace SystemPensSystemBrushes

{

    public partial class Form1 : Form

    {

        public Form1()

        {

             InitializeComponent();

        }

        private void Form1_Paint(object sender, PaintEventArgs e)

        {

            Graphics g = e.Graphics;

            //Create a pen using SystemPens

            Pen pn = SystemPens.FromSystemColor(SystemColors.HotTrack);

            //Create a brush using SystemBrushes

            SolidBrush brush = (SolidBrush)SystemBrushes.FromSystemColor(SystemColors.ActiveCaption);

            //Draw lines and rectangles

            g.DrawLine(pn, 20, 20, 20, 100);

            g.DrawLine(pn, 20, 20, 100, 20);

             g.FillRectangle(brush, 30, 30, 50, 50);

            //YOU CAN'T DISPOSE OF SYSTEM PENS AND 

            //BRUSHES.IF YOU TRY, GDI+ WILL GENERATE 

            //AN ERROR.

            //pn.Dispose ();

            //brush.Dispose ();

        }

    }

}

Figure 4.31 shows the output from Listing 4.26.

FIGURE 4.31: Using system pens and system brushes

Conclusion

Hope the article would have helped you in understanding how to draw a line chart 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.