Advanced MFC Programming

Chapter 8. DC, Pen, Brush and Palette
We can declare a brush type variable using class CBrush, and create various kind of brushes by calling
any of the following functions: CBrush::CreateSolidBrush(…), CBrush::CreateHatchBrush(…),
CBrush::CreatePatternBrush(…). In the sample, only solid brush is used. In Windows, there are several
pre-implemented default GDI objects that can be retrieved and used at any time. These objects include
pens, brushes, fonts, etc. We can get any object by calling ::GetStockObject(…) API function. The
returned value is a handle that could be attached to a GDI variable (declared by MFC class) of the same
type. For example, the following code shows how to obtain a gray brush and attach it to a CBrush type
variable:
CBrush brush;
brush.Attach(::GetStockObject(GRAY_BRUSH));
//After some drawing
brush.Detach();
We need to detach the object before the GDI variable goes out of scope.
When a rectangle is not finally fixed, we may want to draw only its border and leave its interior
unpainted. To implement this, we can select a NULL (hollow) brush into the device context. A hollow
brush can be obtained by calling function ::GetStockObject(…) using HOLLOW_BTRUSH or NULL_BRUSH flag.
Sample 8.2-1\GDI demonstrates how to implement an interactive environment to let the user draw
rectangles. It is an SDI application generated by Application Wizard. Like what we implemented in sample
8.1\GDI, first some member variables and functions are declared in the document for storing rectangles:
……
……
……
class CGDIDoc : public CDocument
{
public:
void AddRect(CRect rect){m_paRects.Add(new CRect(rect));}
CRect *GetRect(int nID){return (CRect *)m_paRects.GetAt(nID);}
int GetNumOfRects(){return m_paRects.GetSize();}
protected:
CPtrArray m_paRects;
};
In the destructor, all the objects in array m_paRects are deleted:
CGDIDoc::~CGDIDoc()
{
while(m_paRects.GetSize())
{
delete m_paRects.GetAt(0);
m_paRects.RemoveAt(0);
}
}
In class CGDIView, some new variables are declared, they will be used to record rectangles, erasing
state and window capture state:
……
……
class CGDIView : public CView
{
protected:
CRect m_rectDraw;
BOOL m_bNeedErase;
BOOL m_bCapture;
};
Two Boolean type variables are initialized in the constructor:
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