如何抓取屏幕中选中区域并存取为bmp位图的类？

/******************************************************************************
* FILE NAME: CopyScreenToBitmap.h *
* *
* DESCRIPTION: *
* 截屏位图文件 *
* *
* COPYRIGHT: *
* (C) Copyright LiuYong *
* All Rights Reserved *
* *
* AUTHOR: *
* liu yong *
* DATE : 2006-11-29 *
* *
*******************************************************************************/
class CCopyScreenToBitmap
{
public:
CCopyScreenToBitmap();
~CCopyScreenToBitmap();
//截取指定区域的屏幕到位图文件，文件目录默认让用户自己选择
BOOL SaveRectToBitmap( LPRECT lpRect, LPSTR lpFileName = NULL );
//截取全屏幕到位图文件，文件目录默认让用户自己选择
BOOL SaveScreenToBitmap( LPSTR lpFileName = NULL );

private:
HBITMAP SaveBitmapCopyScreenToBitmap( LPRECT lpRect );
BOOL SaveBitmapToFile( HBITMAP hBitmap , LPSTR lpFileName ) ;
void SaveBitmapToClipboard( HBITMAP hBitmap, HWND hWnd );

};

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

// CopyScreenToBitmap.cpp: implementation of the CCopyScreenToBitmap class.
//
//////////////////////////////////////////////////////////////////////

#include "stdafx.h"

#include "CopyScreenToBitmap.h"
#include <afxdlgs.h>

#ifdef _DEBUG
#undef THIS_FILE
static char THIS_FILE[]=__FILE__;
#define new DEBUG_NEW
#endif

//////////////////////////////////////////////////////////////////////
// Construction/Destruction
//////////////////////////////////////////////////////////////////////

CCopyScreenToBitmap::CCopyScreenToBitmap()
{

}

CCopyScreenToBitmap::~CCopyScreenToBitmap()
{

}

BOOL CCopyScreenToBitmap::SaveRectToBitmap(LPRECT lpRect, LPSTR lpFileName)
{
if(!lpRect)
{
::MessageBox( NULL,"请指定要截图的区域！","提示",MB_ICONINFORMATION );
return FALSE;
}
HBITMAP hBitmap = SaveBitmapCopyScreenToBitmap(lpRect);
if( !lpFileName )
{
CString Path;

CFileDialog dlg(FALSE,"*.*","新图形",NULL,
"位图文件(*.bmp)|*.bmp|所有文件(*.*)|*.*||",NULL);

//not change the default dir
dlg.m_ofn.Flags |= OFN_EXPLORER|OFN_OVERWRITEPROMPT|OFN_HIDEREADONLY|OFN_NOCHANGEDIR;
dlg.m_ofn.lpstrTitle = "保存图形";

if (dlg.DoModal() == IDCANCEL)
{
::DeleteObject(hBitmap);
return FALSE;
}

Path = dlg.GetPathName();

//save the bitmap
return SaveBitmapToFile(hBitmap,Path.GetBuffer( Path.GetLength() ) );
}
else
{
return SaveBitmapToFile( hBitmap, lpFileName );
}
}

BOOL CCopyScreenToBitmap::SaveScreenToBitmap( LPSTR lpFileName )
{
int cxSrc = GetSystemMetrics (SM_CXSCREEN) ; //源设备宽--屏幕宽
int cySrc = GetSystemMetrics (SM_CYSCREEN) ; //源设备高--屏幕高
CRect rect(0,0,cxSrc,cySrc);

HBITMAP hBitmap = SaveBitmapCopyScreenToBitmap( &rect );
if( !lpFileName )
{
CString Path;

CFileDialog dlg(FALSE,"*.*","新图形",NULL,
"位图文件(*.bmp)|*.bmp|所有文件(*.*)|*.*||",NULL);

//not change the default dir
dlg.m_ofn.Flags |= OFN_EXPLORER|OFN_OVERWRITEPROMPT|OFN_HIDEREADONLY|OFN_NOCHANGEDIR;
dlg.m_ofn.lpstrTitle = "保存图形";

if (dlg.DoModal() == IDCANCEL)
{
::DeleteObject(hBitmap);
return FALSE;
}

Path = dlg.GetPathName();

//save the bitmap
return SaveBitmapToFile(hBitmap,Path.GetBuffer( Path.GetLength() ) );
}
else
{
return SaveBitmapToFile( hBitmap, lpFileName );
}
}

//lpRect 代表选定区域
HBITMAP CCopyScreenToBitmap::SaveBitmapCopyScreenToBitmap(LPRECT lpRect)
{
// 屏幕和内存设备描述表
HDC hScrDC, hMemDC;

// 位图句柄
HBITMAP hBitmap, hOldBitmap;

// 选定区域坐标
int nX, nY, nX2, nY2;

// 位图宽度和高度
int nWidth, nHeight;

// 屏幕分辨率
int xScrn, yScrn;

// 确保选定区域不为空矩形
if (IsRectEmpty(lpRect))
return NULL;

//为屏幕创建设备描述表
hScrDC = CreateDC("DISPLAY", NULL, NULL, NULL);

//为屏幕设备描述表创建兼容的内存设备描述表
hMemDC = CreateCompatibleDC(hScrDC);

// 获得选定区域坐标
nX = lpRect->left;
nY = lpRect->top;
nX2 = lpRect->right;
nY2 = lpRect->bottom;

// 获得屏幕分辨率
xScrn = GetDeviceCaps(hScrDC, HORZRES);
yScrn = GetDeviceCaps(hScrDC, VERTRES);

//确保选定区域是可见的
if (nX < 0)
nX = 0;
if (nY < 0)
nY = 0;
if (nX2 > xScrn)
nX2 = xScrn;
if (nY2 > yScrn)
nY2 = yScrn;

nWidth = nX2 - nX;
nHeight = nY2 - nY;

// 创建一个与屏幕设备描述表兼容的位图
hBitmap = CreateCompatibleBitmap(hScrDC, nWidth, nHeight);

// 把新位图选到内存设备描述表中
hOldBitmap = (HBITMAP)SelectObject(hMemDC, hBitmap);

// 把屏幕设备描述表拷贝到内存设备描述表中
BitBlt(hMemDC, 0, 0, nWidth, nHeight,hScrDC, nX, nY, SRCCOPY);

//得到屏幕位图的句柄
hBitmap = (HBITMAP)SelectObject(hMemDC, hOldBitmap);

//清除
DeleteDC(hScrDC);
DeleteDC(hMemDC);

// 返回位图句柄
return hBitmap;
}

/////得到屏幕位图句柄以后,我们
/////可以把屏幕内容粘贴到剪贴板上.
void CCopyScreenToBitmap::SaveBitmapToClipboard(HBITMAP hBitmap,HWND hWnd)
{
//hWnd为程序窗口句柄
if (OpenClipboard(hWnd))
{
//清空剪贴板
EmptyClipboard();

SetClipboardData(CF_BITMAP, hBitmap);

//关闭剪贴板
CloseClipboard();
}
}

//我们也可以把屏幕内容以位图格式存到磁盘文件上.
//lpFileName 为位图文件名
BOOL CCopyScreenToBitmap::SaveBitmapToFile(HBITMAP hBitmap , LPSTR lpFileName)
{
//设备描述表
HDC hDC;

//当前显示分辨率下每个像素所占字节数
int iBits;

//位图中每个像素所占字节数
WORD wBitCount=32;

//定义调色板大小， 位图中像素字节大小 ，
//位图文件大小 ， 写入文件字节数
DWORD dwPaletteSize=0,
dwBmBitsSize,
dwDIBSize, dwWritten;

//位图属性结构
BITMAP Bitmap;

//位图文件头结构
BITMAPFILEHEADER bmfHdr;

//位图信息头结构
BITMAPINFOHEADER bi;

//指向位图信息头结构
LPBITMAPINFOHEADER lpbi;

//定义文件，分配内存句柄，调色板句柄
HANDLE fh, hDib;
HPALETTE hPal,hOldPal=NULL;

//计算位图文件每个像素所占字节数
hDC = CreateDC("DISPLAY",NULL,NULL,NULL);
iBits = GetDeviceCaps(hDC, BITSPIXEL) * GetDeviceCaps(hDC, PLANES);
DeleteDC(hDC);

if (iBits <= 1)
wBitCount = 1;
else if (iBits <= 4)
wBitCount = 4;
else if (iBits <= 8)
wBitCount = 8;
else if (iBits <= 24)
wBitCount = 24;

//计算调色板大小
if (wBitCount <= 8)
dwPaletteSize = (1 << wBitCount) *sizeof(RGBQUAD);

//设置位图信息头结构
GetObject(hBitmap, sizeof(BITMAP), (LPSTR)&Bitmap);
bi.biSize = sizeof(BITMAPINFOHEADER);
bi.biWidth = Bitmap.bmWidth;
bi.biHeight = Bitmap.bmHeight;
bi.biPlanes = 1;
bi.biBitCount = wBitCount;
bi.biCompression = BI_RGB;
bi.biSizeImage = 0;
bi.biXPelsPerMeter = 0;
bi.biYPelsPerMeter = 0;
bi.biClrUsed = 0;
bi.biClrImportant = 0;

dwBmBitsSize = ((Bitmap.bmWidth *wBitCount+31)/32)* 4*Bitmap.bmHeight ;

//为位图内容分配内存
hDib = GlobalAlloc(GHND,dwBmBitsSize+dwPaletteSize+sizeof(BITMAPINFOHEADER));
lpbi = (LPBITMAPINFOHEADER)GlobalLock(hDib);
*lpbi = bi;

// 处理调色板
hPal = (HPALETTE)GetStockObject(DEFAULT_PALETTE);
if (hPal)
{
hDC = GetDC(NULL);
hOldPal = SelectPalette(hDC, hPal, FALSE);
RealizePalette(hDC);
}

// 获取该调色板下新的像素值
GetDIBits(hDC, hBitmap, 0, (UINT)Bitmap.bmHeight,(LPSTR)lpbi + sizeof(BITMAPINFOHEADER)+dwPaletteSize,(LPBITMAPINFO)lpbi, DIB_RGB_COLORS);

//恢复调色板
if (hOldPal)
{
SelectPalette(hDC, hOldPal, TRUE);
RealizePalette(hDC);
ReleaseDC(NULL, hDC);
}

//创建位图文件
fh = CreateFile(lpFileName, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);

if (fh == INVALID_HANDLE_VALUE)
return FALSE;

//设置位图文件头
bmfHdr.bfType = 0x4D42; // "BM"
dwDIBSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + dwPaletteSize + dwBmBitsSize;
bmfHdr.bfSize = dwDIBSize;
bmfHdr.bfReserved1 = 0;
bmfHdr.bfReserved2 = 0;
bmfHdr.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER) + (DWORD)sizeof(BITMAPINFOHEADER)+ dwPaletteSize;

// 写入位图文件头
WriteFile(fh, (LPSTR)&bmfHdr, sizeof(BITMAPFILEHEADER), &dwWritten, NULL);

// 写入位图文件其余内容
WriteFile(fh, (LPSTR)lpbi, dwDIBSize, &dwWritten, NULL);

//清除
GlobalUnlock(hDib);
GlobalFree(hDib);
CloseHandle(fh);

return TRUE;
}