Accessories for Controls: The Colors


Introduction to Colors



The color is one of the most fundamental aspects used to enhance the aesthetic appearance of a control. It is a non-spatial abstract that is added to an object to modify some of its visual aspects. The Win32 library provides various functions to deal with colors.


Three numeric values are used to create or specify a color. Each one of these values is 8 bits. The first number is called red. The second is called green. The third is called blue:

7 6 5 4 3 2 1 0
7 6 5 4 3 2 1 0
7 6 5 4 3 2 1 0

Converted to decimal, each one of these numbers would produce:

27 + 26 + 25 + 24 + 23 + 22 + 21 + 20 
= 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1
= 255



Therefore, each number can have a value that ranges from 0 to 255 in the decimal system. These three numbers are combined to produce a single value as follows:

Blue Green Red

Converted to decimal, this number has a value of 255 * 255 * 255 = 16581375. This means that we can have approximately 16 million colors available.

Creating a Color

Microsoft Windows characterizes a color as a 32-bit long integer. Therefore, a color is actually a combination of 32 bits. The bits of the most significant byte (the left byte) are reserved for the operating system's internal use and must be set to 0. Based on this, each color is characterized by its combination of a red, a green, and a blue values.

The 32-bit numeric value used by the Win32 library to characterize a color is defined as the COLORREF data type. You can use it to declare a color variable. Here is an example:

procedure TForm1.FormCreate(Sender: TObject);
var ClrMine : COLORREF;
    Color := ClrMine

When or after declaring such a variable, you can initialize it with a 32-bit decimal value. Here is an example:

procedure TForm1.FormCreate(Sender: TObject);
var ClrMine : COLORREF;
    ClrMine := 1637623;
    Color   := ClrMine;

To provide support for colors, the VCL provides the TColor enumerator for the actions you can use to take advantage of the various aspects of colors. The VCL itself defines a color as a member of the TColor enumerator. Although you can use the COLORREF data type to declare or use a color, you should always cast your color variables to TColor. Otherwise, most of the time, you will receive a nevertheless and somewhat harmless warning. For example, the above COLORREF value can be used to colorize the client area of a form after being cast to TColor as follows:

procedure TForm1.FormCreate(Sender: TObject);
var ClrMine : COLORREF;
    ClrMine := 1637623;
    Color   := TColor(ClrMine);

Characteristics of Colors


The Color as a Combination of Red, Green, and Blue Values

Although the above number (1637623) is a legitimate color value, it is difficult to identify and predict as its red, green, and blue values are not known. To create a color value, the Win32 API provides the RGB macro. The RGB macro behaves like a function and requires three numeric values separated by a comma. Each value must range between 0 and 255 both included. Using RGB, the above initialization can be done as follows:

procedure TForm1.FormCreate(Sender: TObject);
var ClrMine : COLORREF;
    ClrMine := RGB(247, 252, 24);
    Color := TColor(ClrMine);

You can also declare a color using the TColor enumerator as a data type. Like any other, the variable can have any valid Pascal name. After declaring the variable, you can initialize it. To do this, you can assign it any long integer value. You can also use the RGB macro to create the color. Whether using a constant long or the RGB macro, you should always cast the value to TColor. Here is an example:

procedure TForm1.FormCreate(Sender: TObject);
    FirstColor : TColor;
    SecondColor : TColor;
    FirstColor := TColor(723873);
    SecondColor := TColor(RGB(247, 252, 24));

You can also initialize a TColor variable using a color name as we will review below.

Decoding a Color

Whether a color was initialized with a 32-bit long integer, the RGB macro, or a valid color name, if you want to retrieve the red, green, and blue values of a color, you can use the GetRValue(), the GetGValue(), and/or the GetBValue() macros to extract the value of each. Each macro takes a 32-bit value as argument, rgb. The GetRValue() macro returns the red value of the rgb parameter. The GetGValue() macro returns the green value of the rgb number. The GetBValue() macro returns the blue value of rgb.

Color Identification

When all three red, green, and blue numbers of a color have their lowest value, which is 0, the color is referred to as black. When the numbers are at their highest value, which is 255, the color qualifies as white. To help with color naming, the VCL provides a list of color identifiers in the graphics.hpp header file. These names can be used throughout any VCL application where a color would be used. To see a list of these colors, on the Object Inspector, click the Color (or any color-related) field and click the arrow of its combo box. The names of colors start with cl.

There are two categories of color names you will use in your applications: those used or configured by the operating system and those defined by the VCL. The colors whose values are controlled by the operating system are set using the Appearance tab of the Display program of Control Panel:

Just like you, because users are able and free to change these colors to their liking, it is almost impossible to predict the appearance of these colors on someone else's computer. Fortunately, if you want to use one of these colors, you can ask your application to check its value on the user's computer. To do this, you can call the GetSysColor() function. This function receives a constant value that is defined in the operating system representing one of the appearance's colors and returns the 32-bit value of that color. The colors defined in Control Panel and/or the VCL and can be passed as the nIndex argument of the GetSysColor() function are:

System Color Role: Color of System Color - nIndex TColor Color Name
3D Objects Background COLOR_3DFACE
3D Objects: Top and Left Edges COLOR_3DHILIGHT
3D Objects: Right and Bottom Edges COLOR_3DDKSHADOW cl3DDkShadow
3D Effect of Buttons and Dialog Boxes: Top and left edges COLOR_3DLIGHT cl3DLight
3D Effect of Buttons and Dialog Boxes: Right and bottom edges COLOR_3DSHADOW
Background of Buttons and Dialog Boxes COLOR_BTNFACE clBtnFace
Text of Buttons COLOR_BTNTEXT clBtnText
General Text on Windows COLOR_WINDOWTEXT  
Active Title Bar COLOR_ACTIVECAPTION clActiveCaption
Active Window Border COLOR_ACTIVEBORDER clActiveBorder
Inactive Window Border COLOR_INACTIVEBORDER clInactiveBorder
Application Background COLOR_BACKGROUND clBackground
Desktop General COLOR_DESKTOP clBackground
Desktop Background COLOR_BACKGROUND clBackground
Inactive Title Bar Background COLOR_INACTIVECAPTION clInactiveCaption
Inactive Title Bar Text COLOR_INACTIVECAPTIONTEXT clInactiveCaptionText
Background of MDI COLOR_APPWORKSPACE clAppWorkSpace
Menu Bar   clMenuBar
Menu Background COLOR_MENU clMenu
Menu Text COLOR_MENUTEXT clMenuText
Menu Highlight   clMenuHighlight
Scrollbar COLOR_SCROLLBAR clScrollBar
Selected Items Background COLOR_HIGHLIGHT clHighlight
Selected Items Text COLOR_HIGHLIGHTTEXT clHighlightText
ToolTip Background COLOR_INFOBK clInfoBk
ToolTip Text COLOR_INFOTEXT clInfoText
Window: Text on Caption COLOR_CAPTIONTEXT clCaptionText
Window Background COLOR_WINDOW clWindow
Window Frame COLOR_WINDOWFRAME clWindowFrame
Window Text COLOR_WINDOWTEXT clWindowText
Right Side of a Gradient Active Window Title Bar COLOR_GRADIENTACTIVECAPTION clGradientActiveCaption
Right Side of a Gradient Inactive Window Title Bar COLOR_GRADIENTINACTIVECAPTION clGradientInactiveCaption
Color of Hot-Track Item (See Tree View) COLOR_HOTLIGHT clHotLight

Besides the system colors defined in the right column, the VCL provides various color names whose values are constant and can be predicted for an application. These colors are clBlack, clMaroon, clGreen, clOlive, clNavy, clPurple, clTeal, clGray, clSilver, clRed, clLime, clYellow, clBlue, clFushsia, clAqua, clLtGray, clDkGray, clWhite, clMoneyGreen, clSkyBlue, clCream, clMedGray, clNone, and clDefault. Remember that you can create any color you want by providing its red, green, and blue value then initialize a TColor variable with it.

Color Palettes

Device independence is the ability for an application to draw its intended figures, text, shapes, and display colors regardless of the device on which the drawing is performed. One way to take care of this is to manage colors at the operating system level so that Microsoft Windows can select the right color to render an object or portion of it. In some cases, a device, such as a monitor or a printer, may need to take care of the coloring details of the job(s) it is asked to perform.

A color palette is a list of colors that a device can display. For example, one device may be able to handle only two colors. Such is the case for a black and white printer. Another device could be able to use more colors than that. To control this situation, Microsoft Windows keeps track of the color palette of each device installed on the computer.

There are two types of color palettes. The default color palette is a list of colors that the operating system would use on a device unless notified otherwise. There are typically 20 reserved colors as default. A logical palette is a palette that an application creates for a specific device context.


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