Advanced MFC Programming

Chapter 11. Sample: Simple Paint
position by calling function CGDIView::DrawPoint(…); for line drawing, we need to first erase the old
drawings by copying the backup bitmap to CGDIView::m_bmpDraw, then draw a new line:
……
……
case TOOL_PEN:
{
if(nFlags & MK_LBUTTON)
{
if(pt != m_ptMouseDown)
{
DrawPoint(point);
pDoc->SetModifiedFlag(TRUE);
}
}
break;
}
case TOOL_LINE:
{
if(nFlags & MK_LBUTTON)
{
ResumeBackupBmp();
DrawLine(m_ptMouseDown, pt);
}
break;
}
The implementation of WM_LBUTTONUP message handler is almost the same with that of WM_MOUSEMOVE
message handler: for dot drawing, a new dot is drawn at the current mouse position by calling function
CGDIView::DrawPoint(…). For line drawing, the backup bitmap is first resumed to CGDIView::m_bmpdraw.
Then a new line is drawn between points represented by CGDIView::m_ptMouseDown and current mouse
position.
Mouse Cursor
It is desirable to change the shape of mouse cursor when it is within the bitmap image. We can either
choose a standard mouse cursor or design our own cursor. A standard cursor can be loaded by calling
function CWinApp::LoadStandardCursor(…). There are many standard cursors that can be used in the
application, which include beam cursor (IDC_IBEAM), cross cursor (IDC_CROSS), etc. The mouse cursor can
be changed by handling WM_SETCURSOR message. In this message handler, we can call ::SetCursor(…) to
change the current cursor shape if we do not want the default arrow cursor.
We need another function to judge if the current mouse cursor is within the bitmap image contained in
the client window. In the sample, function CGDIView::MouseWithinBitmap() is added for this purpose. The
current image ratio and scrolled positions are all taken into consideration when doing the calculation. The
following is the implementation of this function:
BOOL CGDIView::MouseWithinBitmap()
{
CPoint point;
CPoint ptScroll;
CRect rect;
CRect rectBmp;
BITMAP bm;
int nRatio;
CGDIDoc *pDoc;
pDoc=(CGDIDoc *)GetDocument();
nRatio=pDoc->GetRatio();
ptScroll=GetScrollPosition();
::GetCursorPos(&point);
GetWindowRect(rect);
point.Offset(-rect.left, -rect.top);
point.Offset(ptScroll);
ASSERT(m_bmpDraw.GetSafeHandle());
344