GDI Accessories and Tools: Brushes
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GDI Accessories and Tools: Brushes |
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Introduction |
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A brush is a drawing tool used to fill out closed shaped or the interior of lines. A brush behaves like picking up a bucket of paint and pouring it somewhere. In the case of computer graphics, the area where you position the brush is called the brush origin. The color (or picture) that the brush holds would be used to fill the whole area until the brush finds a limit set by some rule. A brush can be characterized by its color (if used), its pattern used to fill the area, or a picture (bitmap) used as the brush. To create a brush, the MFC provides the CBrush class. Therefore, to start, you can declare a variable of this type using the default constructor as follows: CBrush NewBrush; |
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Because there can be so many variations of brushes, there are different member functions for the various possible types of brushes you would need. The easiest brush you can create is made of a color.
A brush is referred to as solid if it is made of a color simply used to fill a closed shaped. To create a solid brush, you can use the following constructor: CBrush(COLORREF crColor); The color to provide as the crColor argument follows the rules we reviewed for colors. To use the newly created brush, you can select it into the device context by calling the CDC::SelectObject(). Once this is done. Any closed shape you draw (ellipse, rectangle, polygon) would be filled with the color specified. After using the brush, you can dismiss it and restore the previous brush. Here is an example:
Once a brush has been selected, it would be used on all shapes that are drawn under it, until you delete or change it. Here is an example:
If you want to use a different brush, you should create a new one. Here is an example:
If you had declared a CBrush variable using the default constructor, you can initialize it with a color by calling the CBrush::CreateSolidBrush() method. Its syntax is: BOOL CreateSolidBrush(COLORREF crColor); This member function can be used in place of the second constructor. It takes the same type of argument, a color as crColor and produces the same result. Here is an example:
A hatch brush is one that uses a drawn pattern to regularly fill an area. Microsoft Windows provides 6 preset patterns for such a brush. To create a hatched brush, you can use the following constructor: CBrush(int nIndex, COLORREF crColor); If you had declared a CBrush variable using the default constructor, you can call the CreateHatchBrush() member function to initialize it. The syntax of this method is: BOOL CreateHatchBrush(int nIndex, COLORREF crColor); In both cases, the nIndex argument specifies the hatch pattern that must be used to fill the area. The possible values to use are HS_BDIAGONAL, HS_CROSS, HS_DIAGCROSS, HS_FDIAGONAL, HS_HORIZONTAL, or HS_VERTICAL. The crColor argument specifies the color applied on the drawn pattern. Here is an example:
A pattern brush is one that uses a bitmap or (small) picture to fill out an area. To create DDB bitmap, you can first create an array of WORD values. Then call the CBitmap::CreateBitmap() method to initialize it. As this makes the bitmap ready, call the CBrush::CreatePatternBrush() method to initialize the brush. The syntax of this member function is: BOOL CreatePatternBrush(CBitmap* pBitmap); Once the brush has been defined, you can select in into a device context and use it as you see fit. For example, you can use it to fill a shape. Here is an example:
Another technique you can use to create a pattern brush consists of using a bitmap resource. Before creating a pattern, you must first have a picture, which can be done by creating a bitmap. For example, imagine you create the following bitmap:
To create a brush based on a bitmap, you can use the following constructor: CBrush(CBitmap* pBitmap); If you had declared a CBrush variable using the default constructor, you can call the CBrush::CreatePatternBrush() member function to initialize it. Its syntax is: BOOL CreatePatternBrush(CBitmap* pBitmap); Here is an example:
The Win32 library provides the LOGBRUSH structure that can be used to create a brush by specifying its characteristics. LOGBRUSH is defined as follows: typedef struct tagLOGBRUSH {
UINT lbStyle;
COLORREF lbColor;
LONG lbHatch;
} LOGBRUSH, *PLOGBRUSH;
The lbStyle member variable specifies the style applied on the brush. The lbColor is specified as a COLORREF value. The lbHatch value represents the hatch pattern used on the brush. Here is an example:
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