Advanced MFC Programming

Chapter 8. DC, Pen, Brush and Palette
}
m_ptEnd=point;
ptrDoc->AddLine(CRect(m_ptStart.x, m_ptStart.y, m_ptEnd.x, m_ptEnd.y));
m_bNeedErase=FALSE;
Invalidate();
if(m_bCapture == TRUE)
{
::ReleaseCapture();
m_bCapture=FALSE;
}
CView::OnLButtonUp(nFlags, point);
Here a dotted pen is created again to erase the old line. Then function CView::GetDocument() is called
to obtain a pointer to the document. After the line information is retrieved from the mouse position,
function CGDIDoc::AddLine(…) is called to add new data to the document. Then flag m_bNeedErase is
cleared, and window capture is released. Finally function CWnd::Invalidate() is called to update the client
window. By default, this action will cause function CView::OnDraw(…) to be called.
For SDI and MDI applications, function CView::OnDraw(…) will be added to the project at the
beginning by Application Wizard. In order to implement our own interface, we need to rewrite this member
function as follows:
void CGDIView::OnDraw(CDC* pDC)
{
CPen pen;
CPen *ptrPenOld;
int nMode;
int nNumOfLines;
int i;
CRect *ptrRect;
CGDIDoc *pDoc=GetDocument();
ASSERT_VALID(pDoc);
}
pen.CreatePen(PS_SOLID, 1, RGB(255, 0, 0));
ptrPenOld=pDC->SelectObject(&pen);
nMode=pDC->SetROP2(R2_COPYPEN);
nNumOfLines=pDoc->GetNumOfLines();
for(i=0; iGetLine(i);
pDC->MoveTo(ptrRect->TopLeft());
pDC->LineTo(ptrRect->BottomRight());
}
pDC->SetROP2(nMode);
pDC->SelectObject(ptrPenOld);
In the above function CPen::CreatePen(…) is called to create a red solid pen whose width is 1 device
unit. Since the window DC is passed as a parameter to this funciton, we do not need to call CWnd::GetDC()
or declare CClientDC type variable to obtain window’s device context. After the pen is selected into the
DC, the drawing mode is set to R2_COPYPEN, which will output the pen’s color to the target device. Next
function CGDIDoc::GetNumOfLines() is called to retrieve the total number of lines stored in the document.
Then a loop is used to draw every line in the client window. Finally the DC’s original drawing mode is
resumed and the new pen is selected out of it.
8.2 Rectangle and Ellipse
It is easy to implement rectangle drawing after we understand the previous sample. To draw a
rectangle, we need to call function CDC::Rentangle(…) and pass a CRect type value to it. The rectangle’s
border will be drawn using current pen selected by the DC, and its interior will be filled with the currently
selected brush.
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