Advanced MFC Programming

Chapter 11. Sample: Simple Paint
void CGDIView::DrawLine(CPoint ptStart, CPoint ptEnd);
This function draws a line on the bitmap from point ptStart to ptend using the current foreground
color, which is stored in the document. The input parameters must be normalized points.
void CGDIView::BackupCurrentBmp();
For the purpose of backing up the current bitmap, a new CBitmap type variable m_bmpBackup is
declared in class CGDIView. When function CGDIView::BackupCurrentBmp() is called, we create a new
bitmap and attaches it to m_bmpBackup then initialize the bitmap with the current bitmap image
(CGDIView:: m_bmpDraw).
void CGDIView::ResumeBackupBmp();
This function does the opposite of the previous function, it copies the bitmap stored in CGDIView::
m_bmpBackup to CGDIView::m_bmpDraw.
With the above new functions, we are able to implement dot and line drawing. To implement
interactive line drawing, another new variable m_ptMouseDown is declared in class CGDIView. This variable
is used to record the position of mouse cursor when its left button is being pressed down. As the mouse
moves or the left button is released, we can use it along with the new mouse position to draw a straight line.
The following is the implementation of WM_LBUTTONDOWN message handler:
void CGDIView::OnLButtonDown(UINT nFlags, CPoint point)
{
int nCurrentTool;
CGDIDoc *pDoc;
}
if(m_bmpDraw.GetSafeHandle() != NULL)
{
pDoc=(CGDIDoc *)GetDocument();
nCurrentTool=pDoc->GetCurrentTool();
SetCapture();
m_ptMouseDown=NormalizePtPosition(point);
switch(nCurrentTool)
{
case TOOL_PEN:
{
DrawPoint(m_ptMouseDown);
pDoc->SetModifiedFlag(TRUE);
break;
}
case TOOL_LINE:
{
BackupCurrentBmp();
DrawPoint(m_ptMouseDown);
pDoc->SetModifiedFlag(TRUE);
break;
}
}
}
CScrollView::OnLButtonDown(nFlags, point);
After left button of the mouse is pressed down, we must set window capture in order to receive mouse
messages even when the cursor is not within the client window. The window capture is released when the
left button is released. If the current drawing object is dot, we need to call function CGDIView::
DrawPoint(…) to draw the dot at the current mouse position; if the current drawing object is line, we need
to first backup the current bitmap then draw a dot at the current mouse position.
For WM_MOUSEMOVE message, first we must check if the left button is being held down. If so, we can
further proceed to implement drawing. For dot drawing, we need to draw a new dot at the current mouse
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