Use line to introduce hdc cdc cclientdc cwindowdc usage

Create a project with a single document structure

HDC:

First, add windows message handler in the cyourclassview class. One is lbuttondown and the other is lbuttonup. Add the member variable m_ptorigin to record the initial vertex position.

Initialize the m_ptorigin variable in the view struct:

Cyourclassview: cyourclassview ()

{

// Todo: Add construction code here

M_ptorigin = 0;

}

Add the code to the lbuttondown function:

Void cyourclassview: onlbuttondown (uint nflags, cpoint point)

{

// Todo: add your message handler code here and/or call default

M_ptorigin = point;

Cview: onlbuttondown (nflags, point );

}

Add code in lbuttonup, first use HDC:

Void cyourclassview: onlbuttonup (uint nflags, cpoint point)

{

// Todo: add your message handler code here and/or call default

HDC;

HDC =: getwindowdc (m_hwnd );

Movetoex (HDC, m_ptorigin.x, m_ptorigin.y, null );

Lineto (HDC, point. X, point. y );

: Releasedc (m_hwnd, HDC );

Cview: onlbuttonup (nflags, point );

}

Use CDC:

Void cyourclassview: onlbuttonup (uint nflags, cpoint point)

{

// Todo: add your message handler code here and/or call default

CDC * PDC = getdc ();

PDC-> moveTo (m_ptorigin );

PDC-> lineto (point );

Releasedc (PDC );

Cview: onlbuttonup (nflags, point );

}

Use cclientdc:

Void cyourclassview: onlbuttonup (uint nflags, cpoint point)

{

// Todo: add your message handler code here and/or call default

Cclientdc DC (this );

DC. moveTo (m_ptorigin );

DC. lineto (point );

Cview: onlbuttonup (nflags, point );

}

Use cwindowdc:

Void cyourclassview: onlbuttonup (uint nflags, cpoint point)

{

// Todo: add your message handler code here and/or call default

Cwindowdc DC (this );

DC. moveTo (m_ptorigin );

DC. lineto (point );

Cview: onlbuttonup (nflags, point );

}