孙鑫VC学习笔记：第四讲 MFC消息映射机制和CDC类的使用

MFC的消息映射机制

------------------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;
}
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---------------------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.*/

实现画线函数

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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);
}

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MSDN

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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

);

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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

使用CDC类完成画线的功能.

CDC* GetDC();

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DrawView.CPP

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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);
}
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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

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CClientDC::CClientDCSee Also

Constructs a CClientDC object that accesses the client area of the CWnd pointed

to by pWnd.

explicit CClientDC(

CWnd* pWnd

);

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（如需访问整个电脑屏幕，使用CWnd::GetDesktopWindow 函数）

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

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

);

CDC::SelectObject

MSDN

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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

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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);

}

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创建画刷

CBrush类

MSDN

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CBrush::CBrush

Constructs a CBrush object.

CBrush( );

CBrush(

COLORREF crColor

);

CBrush(

int nIndex,

COLORREF crColor

);

explicit CBrush(

CBitmap* pBitmap

);

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DrawView.CPP

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void CDrawView::OnLButtonUp(UINT nFlags, CPoint point)

{

// TODO: Add your message handler code here and/or call default

CBrush brush(RGB(255,0,0)); //创建画刷

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);

}

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创建位图的画刷:

CBitmap类

MSDN

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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.

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LoadBitmap函数,加载位图

MSDN

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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

);

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DrawView.CPP

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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);

}

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透明画刷的创建

CBrush::FromHandle

MSDN

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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

);

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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

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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);

}

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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.