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The ToArgb and ToKnownColor methods convert an ARGB or KnownColor value, respectively, to a Color structure.

Listing 5.1 illustrates different ways to create Color objects and use them in an application to draw various graphics objects, including a filled ellipse with a red brush, a filled rectangle with a blue brush, and a line with a green pen. The application first creates four Color objects via the FromArgb , FromName , FromKnownColor , and Empty methods. The FromArgb method creates a translucent pure red Color object, using parameters 120, 255, 0, and 0. The FromName method creates a Color object from the string "Blue". The FromKnownColor method creates a color object from the known color Green .

Listing 5.1 Using the methods and properties of the Color structure

private void ColorStructMenu_Click(object sender, System.EventArgs e) { // Create Graphics object Graphics g = this.CreateGraphics(); // Create Color object from ARGB Color redColor = Color.FromArgb(120, 255, 0, 0); // Create Color object form color name Color blueColor = Color.FromName("Blue"); // Create Color object from known color Color greenColor = Color.FromKnownColor(KnownColor.Green); // Create empty color Color tstColor = Color.Empty; // See if a color is empty if(tstColor.IsEmpty) { tstColor = Color.DarkGoldenrod; } // Create brushes and pens from colors SolidBrush redBrush = new SolidBrush(redColor); SolidBrush blueBrush = new SolidBrush(blueColor); SolidBrush greenBrush = new SolidBrush(greenColor); Pen greenPen = new Pen(greenBrush, 4); // Draw GDI+ objects g.FillEllipse(redBrush, 10, 10, 50, 50); g.FillRectangle(blueBrush, 60, 10, 50, 50); g.DrawLine(greenPen, 20, 60, 200, 60); // Check property values MessageBox.Show("Color Name :"+ blueColor.Name + ", A:"+blueColor.A.ToString() + ", R:"+blueColor.R.ToString() + ", B:"+blueColor.B.ToString() + ", G:"+blueColor.G.ToString() ); // Dispose of GDI+ objects redBrush.Dispose(); blueBrush.Dispose(); greenBrush.Dispose(); greenPen.Dispose(); g.Dispose(); }

Figure 5.1 shows the output from Listing 5.1.

The GetBrightness , GetHue , and GetSaturation methods return a color's brightness, hue, and saturation component values, respectively. Listing 5.2 reads the hue, saturation, and brightness components of a color and displays their values on the form by using the DrawString method.

Listing 5.2 Getting brightness, hue, and saturation of a color

private void HSBMenu_Click(object sender, System.EventArgs e) { // Create a Graphics object Graphics g = this.CreateGraphics(); // Create a color Color clr = Color.FromArgb(255, 200, 0, 100); // Get hue, saturation, and brightness components float h = clr.GetHue(); float s = clr.GetSaturation(); float v = clr.GetBrightness(); string str = "Hue: "+ h.ToString() + "\n" + "Saturation: "+ s.ToString() + "\n" + "Brightness: "+ v.ToString(); // Display data g.DrawString(str, new Font("verdana", 12), Brushes.Blue, 50, 50); // Dispose of object g.Dispose(); }

Figure 5.2 shows the output from Listing 5.2. The values of hue, saturation, and brightness in this particular color are 330, 1, and 0.3921569, respectively.

5.2.3 System Colors

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 Windows controls. In this code we set the background colors of a text box, 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.

Table 5.1. SystemColors properties

SolidBrush brush = new SolidBrush(SystemColors.ActiveCaption); Pen pn = new Pen(SystemColors.HighlightText);

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 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

private void SystemColorsMenu_Click(object sender, System.EventArgs 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, 170, 170); 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.

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;

5.2.4 The ColorConverter and ColorTranslator Classes

The ColorConverter class is used to convert colors from one data type to another. This class is inherited from the TypeConverter class, which defines the functionality for conversion of types and accessing values and properties of types. The TypeConverter class serves as a base class for many conversion classes, and ColorConverter and FontConverter are two of them. We will discuss FontConverter in more detail later in this chapter. Some of the common methods of the TypeConverter class (which are available in the ColorConverter class) are described in Table 5.2.

Table 5.2. Common TypeConverter methods

Listing 5.4 uses the ColorConverter class methods to convert colors. We store a color in a string and call the ConvertFromString method, which returns the Color object. Later we will use the Color objects to create two brushes that we will use to fill a rectangle and an ellipse.

Listing 5.4 Using the ColorConverter class to convert colors

private void ColorConvert_Click(object sender, System.EventArgs e) { Graphics g = this.CreateGraphics(); g.Clear(this.BackColor); string str = "#FF00FF"; ColorConverter clrConverter = new ColorConverter(); Color clr1 = (Color)clrConverter.ConvertFromString(str); // Use colors SolidBrush clr2 = new SolidBrush(clr1); SolidBrush clr3 = new SolidBrush(clr1); // Draw GDI+ objects g.FillEllipse(clr2, 10, 10, 50, 50); g.FillRectangle(clr3, 60, 10, 50, 50); // Dispose of objects clr2.Dispose(); clr3.Dispose(); g.Dispose(); }

Figure 5.4 shows the output from Listing 5.4.

The ColorTranslator class provides methods to translate colors to and from HTML, OLE, and Win32 color values. These methods are useful when you're using legacy color structures that pre-date the .NET Framework. For example, you may have legacy code that gives the HTML color representation of a color. Table 5.3 describes the methods of the ColorTranslator class. All of the methods are static.

Listing 5.5 uses the ColorTranslator class to translate colors from Win32 and HTML colors. Later these colors will be used to create brushes.

Listing 5.5 Translating colors

private void ColorTranslator_Click(object sender, System.EventArgs e) { Graphics g = this.CreateGraphics(); // Translate colors Color win32Color = ColorTranslator.FromWin32(0xFF0033); Color htmlColor = ColorTranslator.FromHtml("#00AAFF"); // Use colors SolidBrush clr1 = new SolidBrush(win32Color); SolidBrush clr2 = new SolidBrush(htmlColor); // Draw GDI+ objects g.FillEllipse(clr1, 10, 10, 50, 50); g.FillRectangle(clr2, 60, 10, 50, 50); // Dispose of objects clr1.Dispose(); clr2.Dispose(); g.Dispose(); }

Table 5.3. ColorTranslator methods

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In a manner similar to the "from" methods just discussed, you can translate a Color structure into Win32, HTML, and OLE values using the ToWin32 , ToHtml , and ToOle methods, respectively.

Note

You can also transform colors using transformation methods. Some of the transformation methods are for scaling, translating, rotating, and shearing . We cover this functionality in Chapter 10.