Advanced MFC Programming

Chapter 11. Sample: Simple Paint
……
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m_ptPrevious=point;
if(m_rgnFreeSel.GetSafeHandle() != NULL)
{
m_rgnFreeSel.DeleteObject();
}
m_dcMem.MoveTo(m_ptMouseDown);
m_dcMem.BeginPath();
For WM_MOUSEMOVE message, we need to draw the freeform outline in the client window and do the
same thing to CGDIView::m_bmpDraw. Note since the current image ratio may not be 1:1, we must use
normalized points when recording path:
……
……
pPenOld=dc.SelectObject(&m_penDot);
dc.MoveTo(m_ptPrevious);
dc.LineTo(point);
m_ptPrevious=point;
dc.SelectObject(pPenOld);
m_dcMem.LineTo(pt);
For WM_LBUTTONUP message, we need to draw the last segment of outline, close the figure, and end the
path. Then we need to create the region from path, and set the dimension of the tracker to the dimension of
the bounding box of the selected region. Again we must consider ratio conversion here: since the path is
recorded with a ratio of 1:1, we must scale its bounding box to the current image ratio. In the sample,
function CGDIView::UnnormalizeTrackerRect(…) is added to scale a normalized rectangle to the current
image ratio. The rest thing needs to be done is the same with that of rectangular selection: we need to back
up the whole image as well as the selected area:
……
……
pPenOld=dc.SelectObject(&m_penDot);
dc.MoveTo(m_ptPrevious);
dc.LineTo(point);
dc.SelectObject(pPenOld);
m_dcMem.LineTo(pt);
m_dcMem.CloseFigure();
m_dcMem.EndPath();
m_rgnFreeSel.CreateFromPath(&m_dcMem);
m_rgnFreeSel.GetRgnBox(rect);
m_trackerSel.m_rect=UnnormalizeTrackerRect(rect);
BackupCurrentBmp();
BackupSelection();
Invalidate(FALSE);
Resizing and Moving the Freeform Selection
Resizing and moving the freeform selection is almost the same with that of rectangular selection,
except that before copying the selected area, we must offset or resize the region and select it into the target
DC. The following portion of function CGDIView::OnLButtonDown(…) shows how the region is resized and
selected into the target memory DC, and how the selected image is copied back:
……
::ReleaseCapture();
m_trackerSel.Track(this, point);
ResumeBackupBmp();
m_rgnFreeSel.GetRgnBox(rectOrgTracker);
rectCurTracker=NormalizeTrackerRect(m_trackerSel.m_rect);
nCount=m_rgnFreeSel.GetRegionData(NULL, 0);
lpRgnData=(LPRGNDATA)new BYTE[nCount];
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