孙鑫VC学习笔记：第四讲 MFC消息映射机制和CDC类的使用

1.在文档-视图结构中,View类总是覆盖在CMainFrm框架窗口之上的.所以框架窗口无法对
WM_LBUTTONDOWN消息做出响应.

2.在添加WM_LBUTONDOWN后,查看我们的工程的源程序变化
<1>查看 DrawView.h
-----------------------------------------------------------------------------------
protected:
//{{AFX_MSG(CDrawView)    //注释宏
afx_msg void OnLButtonDown(UINT nFlags, CPoint point); //消息响应函数原型的声明.
//}}AFX_MSG
-----------------------------------------------------------------------------------
afx_msg 也是一个宏,指明后面的函数是消息响应函数
<2>查看 DrawView.cpp
-----------------------------------------------------------------------------------
    BEGIN_MESSAGE_MAP(CDrawView, CView)
//{{AFX_MSG_MAP(CDrawView)
ON_WM_LBUTTONDOWN() //通过这个宏,把消息和我们的消息响应函数
                      //CDrawView::OnLButtonDown(UINT nFlags, CPoint point)
       //关联起来
//}}AFX_MSG_MAP
// Standard printing commands
ON_COMMAND(ID_FILE_PRINT, CView::OnFilePrint)
ON_COMMAND(ID_FILE_PRINT_DIRECT, CView::OnFilePrint)
ON_COMMAND(ID_FILE_PRINT_PREVIEW, CView::OnFilePrintPreview)
    END_MESSAGE_MAP()
-----------------------------------------------------------------------------------

3.MFC的消息映射机制
查看MFC的源代码:WINCORE.CPP
---------------------------------------------------------------------------------
LRESULT CWnd::WindowProc(UINT message, WPARAM wParam, LPARAM lParam)
{
// OnWndMsg does most of the work, except for DefWindowProc call
LRESULT lResult = 0;
if (!OnWndMsg(message, wParam, lParam, &lResult))//真正的消息处理都是由OnWndMsg
                                                  //函数进行处理的
  lResult = DefWindowProc(message, wParam, lParam);
return lResult;
}
---------------------------------------------------------------------------------

查看AFX_WIN.h
---------------------------------------------------------------------------------
virtual LRESULT WindowProc(UINT message, WPARAM wParam, LPARAM lParam);
--------------------------------------------------------------------------------
//WindowProc(UINT message, WPARAM wParam, LPARAM lParam);是一个虚函数

/*在MFC中维护了一张消息到窗口的对应表,当接收到一个消息后,通过消息的句柄,找到与其相
关联的窗口对象的指针,然后传给CWnd::WindowProc函数,CWnd::WindowProc函数函数交由
CWnd::OnWndMsg函数进行处理,判断子类是否有这个消息的响应函数,通过查看这个类的头文件
看有没有消息响应函数原型的声明,查看源文件,看有没有消息响应函数的定义.如果子类有,那
么交由子类处理消息,如果子类没有,消息交由父类进行处理.*/

4.实现我们的画线函数
---------------------------------------------------------------------------------
   void CDrawView::OnLButtonDown(UINT nFlags, CPoint point)
   {
  // TODO: Add your message handler code here and/or call default
  //MessageBox("View Clicled!");
  m_ptOrigin=point;
  CView::OnLButtonDown(nFlags, point);
   }

void CDrawView::OnLButtonUp(UINT nFlags, CPoint point)
{
  // TODO: Add your message handler code here and/or call default
  HDC hdc;
  hdc=::GetDC(m_hWnd); //每个从CWnd类派生出来的类都有一个内部的数据成员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);
}

---------------------------------------------------------------------------------

MSDN
----------------------------------------------------------------------------------
BOOL MoveToEx(
HDC hdc,          // handle to device context
int X,            // x-coordinate of new current position
int Y,            // y-coordinate of new current position
LPPOINT lpPoint   // old current position
);
BOOL LineTo(
HDC hdc,    // device context handle
int nXEnd, // x-coordinate of ending point
int nYEnd   // y-coordinate of ending point
);
----------------------------------------------------------------------------------

5.CDC类
MFC把所有和窗口相关的操作都封装在CWnd类中.同样,MFC把所有和绘图相关的操作也封装在
CDC类中.
class CDC :public CObject
{
.........................
};
使用CDC类完成画线的功能.
MSDN
----------------------------------------------------------------------------------
CWnd::GetDC
Retrieves a pointer to a common, class, or private device context for the client
area depending on the class style specified for the CWnd.

CDC* GetDC();
----------------------------------------------------------------------------------
DrawView.CPP
---------------------------------------------------------------------------------
void CDrawView::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);
}
---------------------------------------------------------------------------------
6.使用CClientDC
CClientDC派生自CDC
构造CClientDC对象的时候自动调用GetDC,而在析构的时候自动调用ReleaseDC.从而我们不需要
显示的去调用这两个函数.只需要仅仅构造一个CClientDC对象.
MSDN
-----------------------------------------------------------------------------------
CClientDC::CClientDCSee Also
Constructs a CClientDC object that accesses the client area of the CWnd pointed
to by pWnd.

explicit CClientDC(
        CWnd* pWnd
     );
-----------------------------------------------------------------------------------
构造的时候需要一个CWnd*
DrawView.CPP
-----------------------------------------------------------------------------------
void CDrawView::OnLButtonUp(UINT nFlags, CPoint point)
{
// TODO: Add your message handler code here and/or call default
//CClientDC dc(this);
    CClientDC dc(GetParent());//获得父窗口(框架窗口的句柄)
dc.MoveTo(m_ptOrigin);
dc.LineTo(point);
}

7.CWindowDC
class CWindowDC : public CDC
构造CWindowDC对象时,自动调用GetWindowDC,析构时自动调用ReleaseDC.
有了CWindowDC对象我们可以访问整个屏幕区域,包括客户区域和非客户区域.
MSDN
----------------------------------------------------------------------------------
CWindowDC::CWindowDC
     Constructs a CWindowDC object that accesses the entire screen area
(both client and nonclient) of the CWnd object pointed to by pWnd.

     explicit CWindowDC(
        CWnd* pWnd
     );
-----------------------------------------------------------------------------------
DrawView.CPP
-----------------------------------------------------------------------------------
   void CDrawView::OnLButtonUp(UINT nFlags, CPoint point)
   {
// TODO: Add your message handler code here and/or call default
//CWindowDC dc(this);
    CWindowDC dc(GetParent());//获得父窗口(框架窗口的句柄)
dc.MoveTo(m_ptOrigin);
dc.LineTo(point);
   }
-----------------------------------------------------------------------------------

8.CWnd::GetDesktopWindow 函数
MSDN
-------------------------------------------------------------------------------------
CWnd::GetDesktopWindow
Returns the Windows desktop window.

static CWnd* PASCAL GetDesktopWindow( );
-------------------------------------------------------------------------------------
DrawView.CPP
-----------------------------------------------------------------------------------
   void CDrawView::OnLButtonUp(UINT nFlags, CPoint point)
   {
// TODO: Add your message handler code here and/or call default
//CWindowDC dc(this);
    CWindowDC dc(GetDesktopWindow());//获得桌面窗口句柄
dc.MoveTo(m_ptOrigin);
dc.LineTo(point);
   }
-----------------------------------------------------------------------------------

9.画出其他颜色的线条

CPen类
封装了和画笔相关的操作.
CPen的构造函数
MSDN
-----------------------------------------------------------------------------------
Constructs a CPen object.

CPen( );
CPen(
    int nPenStyle,       //笔的风格 PS_SOLID   Creates a solid pen.
                            //PS_DASH   Creates a dashed pen. Valid only when the
       //pen width is 1 or less, in device units.
                            //PS_DOT   Creates a dotted pen.........
    int nWidth,          //线条的宽度
    COLORREF crColor     //笔的颜色
);
CPen(
    int nPenStyle,
    int nWidth,
    const LOGBRUSH* pLogBrush,
    int nStyleCount = 0,
    const DWORD* lpStyle = NULL
);
-----------------------------------------------------------------------------------
RGB宏
MSDN
-----------------------------------------------------------------------------------
COLORREF RGB(
   BYTE byRed,    // red component of color
   BYTE byGreen, // green component of color
   BYTE byBlue    // blue component of color
);               //RGB(0,0,0)Black,RGB(255,255,255)White
-----------------------------------------------------------------------------------
CDC::SelectObject
MSDN
-------------------------------------------------------------------------------------
CDC::SelectObject
Selects an object into the device context.

CPen* SelectObject(
    CPen* pPen
);
CBrush* SelectObject(
    CBrush* pBrush
);
virtual CFont* SelectObject(
    CFont* pFont
);
CBitmap* SelectObject(
    CBitmap* pBitmap
);
int SelectObject(
    CRgn* pRgn
);
CGdiObject* SelectObject(
    CGdiObject* pObject
);
------------------------------------------------------------------------------------

DrawView.CPP
-----------------------------------------------------------------------------------
   void CDrawView::OnLButtonUp(UINT nFlags, CPoint point)
   {
// TODO: Add your message handler code here and/or call default

  CPen pen(PS_SOLID,1,RGB(255,0,0)); //创建画笔
  CClientDC dc(this);
  CPen *pOldPen=dc.SelectObject(&pen);//把创建的画笔选进设备描述表
  dc.MoveTo(m_ptOrigin);
  dc.LineTo(point);
  dc.SelectObject(pOldPen); //还原设备描述表
  CView::OnLButtonUp(nFlags, point);
   }
-----------------------------------------------------------------------------------
10.创建画刷
CBrush类
MSDN
---------------------------------------------------------------------------------
CBrush::CBrush
Constructs a CBrush object.

CBrush( );
CBrush(
    COLORREF crColor
);
CBrush(
    int nIndex,
    COLORREF crColor
);
explicit CBrush(
    CBitmap* pBitmap
);
---------------------------------------------------------------------------------

CView::OnLButtonUp(nFlags, point);
}
-----------------------------------------------------------------------------------

创建位图的画刷:
CBitmap类
MSDN
-----------------------------------------------------------------------------------
CBitmap::CBitmap
Constructs a CBitmap object.

CBitmap( ); // 需要使用函数对其进行初始化
Remarks
The resulting object must be initialized with one of the initialization member
functions.
-------------------------------------------------------------------------------------
LoadBitmap函数,加载位图
MSDN
-------------------------------------------------------------------------------------
CBitmap::LoadBitmap
Loads the bitmap resource named by lpszResourceName or identified by the ID number
in nIDResource from the application's executable file.

BOOL LoadBitmap(
    LPCTSTR lpszResourceName
);
BOOL LoadBitmap(
    UINT nIDResource
);
-------------------------------------------------------------------------------------
DrawView.CPP
-----------------------------------------------------------------------------------
   void CDrawView::OnLButtonUp(UINT nFlags, CPoint point)
   {
// TODO: Add your message handler code here and/or call default

  CBitmap bitmap;
  bitmap.LoadBitmap(IDB_BITMAP1); //加载位图
  CBrush brush(&bitmap);
  CClientDC dc(this);
  dc.FillRect(CRect(m_ptOrigin,point),&brush);//用制定的画刷,填充矩形区域

CView::OnLButtonUp(nFlags, point);
}
-----------------------------------------------------------------------------------

透明画刷的创建
CBrush::FromHandle
MSDN
-------------------------------------------------------------------------------------
CBrush::FromHandle
Returns a pointer to a CBrush object when given a handle to a Windows HBRUSH object.

static CBrush* PASCAL FromHandle(
    HBRUSH hBrush                        //这是CBrush类的静态方法
    //在静态的成员函数中,是不能引用非静态的数据成员
    //因为非静态的数据成员,是在类实例化一个对象时才分配内存空间的.
    //静态的数据成员使用之前必须初始化
);
-------------------------------------------------------------------------------------
由CBrush::FromHandle可以从一个画刷的句柄,得到指向这个画刷对象的指针.
DrawView.CPP
-----------------------------------------------------------------------------------
   void CDrawView::OnLButtonUp(UINT nFlags, CPoint point)
   {
// TODO: Add your message handler code here and/or call default

  CClientDC dc(this);
  CBrush *pBrush=CBrush::FromHandle((HBRUSH)GetStockObject(NULL_BRUSH));
  CBrush *pOldBrush=dc.SelectObject(pBrush);
  dc.Rectangle(CRect(m_ptOrigin,point));
  dc.SelectObject(pOldBrush);
  CView::OnLButtonUp(nFlags, point);
   }
-----------------------------------------------------------------------------------

11.设置绘图模式(CDC::SetROP2)
CDC::SetROP2函数
MSDN
------------------------------------------------------------------------------------
CDC::SetROP2
Sets the current drawing mode.
int SetROP2(
       int nDrawMode
);
Parameters
nDrawMode
Specifies the new drawing mode. It can be any of the following values:
R2_BLACK   Pixel is always black.
R2_WHITE   Pixel is always white.
R2_NOP   Pixel remains unchanged.
R2_NOT   Pixel is the inverse of the screen color.
R2_COPYPEN   Pixel is the pen color.
R2_NOTCOPYPEN   Pixel is the inverse of the pen color.

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