Advanced MFC Programming

Chapter 8. DC, Pen, Brush and Palette
……
}
dc.Ellipse(m_rectDraw);
……
……
void CGDIView::OnDraw(CDC* pDC)
{
}
ptrPenOld=pDC->SelectObject(&pen);
brush.CreateHatchBrush(HS_CROSS, RGB(255, 0, 255));
ptrBrushOld=pDC->SelectObject(&brush);
nMode=pDC->SetROP2(R2_COPYPEN);
nNumOfRects=pDoc->GetNumOfRects();
for(i=0; iEllipse(pDoc->GetRect(i));
}
In CGDIView::OnDraw(…), function CBrush::CreateSolidBrush(…) is also changed to CBrush::
CreateHatchBrush(…). By doing this, a different brush will be used to fill the interior of ellipse.
8.3 Curve
We can call function CDC::PolyBezier(…) to draw curves. This function has two parameters:
BOOL CDC::PolyBezier(const POINT* lpPoints, int nCount);
The first parameter lpPoints is a pointer to an array of points, which specify the control points that
can be used for drawing a curve. The second parameter nCount specifies how many control points are
included in the array. We need at least four control points to draw a curve, although the last three points
could be the same (In this case, a straight line will be drawn).
Sample 8.3\GDI demonstrates how to implement an interactive environment that can let the user draw
curves. It is a standard SDI application generated by Application Wizard. First new variable and functions
are declared in the document, which will be used to store the data of curves:
……
……
……
class CGDIDoc : public CDocument
{
public:
void AddPoint(CPoint pt){m_dwaPts.Add(pt.x); m_dwaPts.Add(pt.y);}
int GetNumOfPts(){return m_dwaPts.GetSize()/2;}
CPoint GetOnePt(int nID)
{
return CPoint(m_dwaPts.GetAt(nID*2), m_dwaPts.GetAt(nID*2+1));
}
protected:
CDWordArray m_dwaPts;
};
We use a CDWordArray type variable m_dwaPts to record control points, this class can be used to record
DWORD type value, which is 32-bit integer. Because a point contains two integers, we need two DWORD type
variables to store one point. So in CGDIDoc::AddPoint(…), function CDWordArray::Add(…) is called twice
to add both x and y coordinates to the array. Function CGDIDoc::GetNumOfPts() returns the number of
control points, which is obtained through dividing the size of the array by 2. Function
CGDIDoc::GetOnePt() returns a specified control point, which is obtained from two consecutive elements
contained in array m_dwaPts.
Curve drawing is implemented in function CGDIView::OnDraw(…) as follows:
211