System Colors in GDI+

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

The SystemColors class represents the Windows system colors; it provides 26 read-only properties, each of which returns a Color object. Table 5.1 lists the properties of the SystemColors class.

The following code snippet uses the SystemColors class to set colors of a few Window controls. In this code we set the background colors of a textbox, a radio button, and a button to inactive border, active caption, and control dark system colors, respectively.

            textBox1.BackColor = SystemColors.InactiveBorder;

            radioButton1.BackColor = SystemColors.ActiveCaption;

            button1.BackColor = SystemColors.ControlDarkDark;

If you're wondering whether you can create a brush or a pen from the SystemColors class to fill and draw shapes, curves, and text, the answer is, absolutely. The following code snippet uses SystemColors to create SolidBrush and Pen objects. This code creates a solid brush and a pen from active caption system and highlight text system colors, respectively.

            SolidBrush brush = new SolidBrush(SystemColors.ActiveCaption);

            Pen pn = new Pen(SystemColors.HighllightText);

TABLE 5.1 SystemColor Properties

Property	Description
ActiveBorder	Active window border color
ActiveCaption	Active window title bar background color
ActiveCaptionText	Active window title bar text color
AppWorkspace	Multiple-document interface (MDI) workspace background color
Control	Control background color
ControlDark	3D control shadow color
ControlDarkDark	3D control dark shadow color
ControlLight	3D control highlight color
ControlLightLight	3D control light highlight color
ControlText	Text color of controls
Desktop	Window desktop color
GrayText	Disabled text color
HighLight	Highlighted text background color
HeighlightText	Highlighted text color
HotTrack	Hot track color
InactiveBorder	Inactive window border color
InactiveCaption	Inactive window caption bar color
InactiveCaptionText	Inactive window caption bar text color
Info	ToolTip background color
InfoText	ToolTip text color
Menu	Menu background color
MenuText	Menu text color
ScrollBar	Background color of scroll bars
Window	Background color of window
WindowFrame	Thin window frame color
WindowText	Window text color

For performance reasons, GDI+ provides SystemPens and SystemBrushes classes, which should be used instead of creating a brush or pen from the SystemColors class. For example, the following method is advisable for creating system brushes and pens. This code snippet creates a solid brush and a pen from active caption and highlight text system colors, respectively.

            SolidBrush brush1 = (SolidBrush)SystemBrushes.FromSystemColor

            (SystemColors.ActiveCaption);

            Pen pn1 = SystemPens.FromSystemColor

            (SystemColors.HighlightText);

Listing 5.3 uses the SystemBrushes and SystemPens classes to create a SolidBrush object and three Pen objects, which are used later to draw and fill graphics objects. The solid brush is created from the active caption system color, and the three pens are created from highlight text, control light, and control dark system colors, respectively. Later the brush and pens are used to draw two lines, a rectangle, and an ellipse.

LISTING 5.3: Using SystemPens and SystemBrushes

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 WindowsFormsApplication2

{

     public partial class Form1 : Form

    {

        public Form1()

        {

             InitializeComponent();

        }

        private void Form1_Load(object sender, EventArgs e)

        {          

        }

        private void Form1_Paint(object sender, PaintEventArgs e)

        {

             //Create a Graphics object

            Graphics g = this.CreateGraphics();

             //Create brushes and pens 

            SolidBrush brush1 = (SolidBrush)SystemBrushes.FromSystemColor

                (SystemColors.ActiveCaption);

            Pen pn1 = SystemPens.FromSystemColor

                (SystemColors.HighlightText);

            Pen pn2 = SystemPens.FromSystemColor

                (SystemColors.ControlLightLight);

            Pen pn3 = SystemPens.FromSystemColor

                (SystemColors.ControlDarkDark);

             //Draw and fill graphics objects

            g.DrawLine(pn1, 10, 10, 10, 200);

             g.FillRectangle(brush1, 60, 60, 100, 100);

            g.DrawEllipse(pn3, 20, 20, system-colors-in-gdi0, system-colors-in-gdi0);

            g.DrawLine(pn2, 10, 10, 200, 10);

             //Dispose of object

            g.Dispose();

        }

    }

}

Figure 5.3 shows the output from Listing 5.3. System colors were used to draw two lines, an ellipse, and a rectangle.

Figure 5.3: Using system colors to draw graphics object

Note: When you create pens using SystemPens, you cannot modify the width or other properties of the pen .The code will compile but will throw an unhandled exception when executed .If you create a pen using SystemColors, however, you can modify its width like this:

            Pen pn = new Pen(SystemColors.HighlightText);

            Pn.Width = 4;

Conclusion

Hope the article would have helped you in understanding System Colors 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.