Usage of MFC CRectTracker

1. Base concept and principle on how to use CRectTracker:
Allows an item to be displayed, moved, and resized in different fashions.
--Form MSDN
Example to use this (when you drag the mouse, the RectTracker comes):
1) QQ Snap Desktop picture;
2) Windows explorer;
....

2. Important member funtions of CRectTracker:
SetRect        // set the rect of rect tracker
Track          // change the position of rect tracker
SetCursor      // Change the cursor
HitTest       
Draw           // draw the rect tracker

Refer MSDN for the Detail.

3. Take an example to show how to use the CRectTracker.
Implement goal show as the follow picture:
 

Environment VS 2008 Windows XP EN

1) start a MFC dialog based project named tracker
2) Add three member:
    CRectTracker m_tracker; // CRectTracker object
    CPoint m_start;         // the the mouse down, record the start point here
    BOOL m_bDraw;           // whether draw

3) Add a WM_LBUTTONDOWN handle function(OnLButtonDown)

void  CtrackerDlg::OnLButtonDown(UINT nFlags, CPoint point)
... {

    int nHitTest;
    nHitTest = m_tracker.HitTest(point);

    if ( nHitTest < 0 )     // if the mouse down point is outside of the rect tracker
    ...{
        m_start = point;    // Record the start drawing point
        m_bDraw = TRUE;     // set m_bDraw (in handle funtion WM_MOUSEMOVE will test this to decide whether to draw)
    }