C++截屏当前活动窗口保存成BMP文件以及BMP文件的比较

#include <time.h>
#include <afxwin.h>
#include <stdio.h>
#include <comdef.h>
#include <iostream>
#include <atlimage.h>

/*
 * hwnd:要截图的窗口的句柄
 * fileName:要比较的图片的路径
 * offsets:有4个成员的int型数组，用于设置比较图片时，上、下、左、右的偏移量
 * offsets[0]：左
 * offsets[1]：上
 * offsets[2]：右
 * offsets[3]：下
 */
bool print_screen(HWND hwnd, const char* fileName, int offsets[])
{
	LPCTSTR pFileName = NULL;

	if(sizeof(TCHAR)==sizeof(char))
    {
        pFileName=(LPCTSTR)fileName;
    }
    else
    {
        int length= sizeof(TCHAR)*(strlen(fileName)+1);
        LPTSTR tcBuffer=new TCHAR[length];
        memset(tcBuffer,0,length);
        MultiByteToWideChar(CP_ACP,0,fileName,strlen(fileName),tcBuffer,length);
        pFileName=(LPCTSTR)tcBuffer ;
    }
	long t_start = ::GetTickCount();
	CDC dc;
	CDC *pDC = &dc;//屏幕DC

        // HWND hwnd = ::GetForegroundWindow(); // 获得当前活动窗口
	HDC activeDC = ::GetWindowDC(hwnd);   //获得要截屏的窗口的hDC

	pDC->Attach(activeDC);//获取当前活动窗口的DC
	RECT rect;
	::GetWindowRect(hwnd,&rect);//得到窗口的大小
	int Width = rect.right - rect.left;

	int Height = rect.bottom - rect.top;

	/*cout << "Width:" << Width << endl

	<< "Height:" << Height << endl << endl;*/

	CDC memDC;//内存DC

	memDC.CreateCompatibleDC(pDC);

	CBitmap memBitmap, *oldmemBitmap;//建立和屏幕兼容的bitmap

	memBitmap.CreateCompatibleBitmap(pDC, Width, Height);

	oldmemBitmap = memDC.SelectObject(&memBitmap);//将memBitmap选入内存DC

	memDC.BitBlt(0, 0, Width, Height, pDC, 0, 0, SRCCOPY);//复制屏幕图像到内存DC
        //以下代码保存memDC中的位图到文件

	BITMAP bmp;

	memBitmap.GetBitmap(&bmp);//获得位图信息

	FILE *fp = fopen("C:\\abc.bmp", "w+b");
	BITMAPINFOHEADER bih = {0};//位图信息头

	bih.biBitCount = bmp.bmBitsPixel;//每个像素字节大小

	bih.biCompression = BI_RGB;

	bih.biHeight = bmp.bmHeight;//高度

	bih.biPlanes = 1;

	bih.biSize = sizeof(BITMAPINFOHEADER);

	bih.biSizeImage = bmp.bmWidthBytes * bmp.bmHeight;//图像数据大小

	bih.biWidth = bmp.bmWidth;//宽度

	BITMAPFILEHEADER bfh = {0};//位图文件头

	bfh.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);//到位图数据的偏移量

	bfh.bfSize = bfh.bfOffBits + bmp.bmWidthBytes * bmp.bmHeight;//文件总的大小

	bfh.bfType = (WORD)0x4d42;

	fwrite(&bfh, 1, sizeof(BITMAPFILEHEADER), fp);//写入位图文件头

	fwrite(&bih, 1, sizeof(BITMAPINFOHEADER), fp);//写入位图信息头

	byte * p = new byte[bmp.bmWidthBytes * bmp.bmHeight];//申请内存保存位图数据

	GetDIBits(memDC.m_hDC, (HBITMAP) memBitmap.m_hObject, 0, Height, p,

		(LPBITMAPINFO) &bih, DIB_RGB_COLORS);//获取位图数据

	fwrite(p, 1, bmp.bmWidthBytes * bmp.bmHeight, fp);//写入位图数据

	delete [] p;

	fclose(fp);

        // 以下代码用于比较指定的BMP文件与内存中的截图
	CImage img;
	img.Load(pFileName);
	int nWidth = img.GetWidth();//获取图像宽度
	int nHeight = img.GetHeight();//获取图像高度
	if (Width != nWidth || Height != nHeight)
	{
		return false;
	}
	byte* pRealData;
	pRealData=(byte*)img.GetBits();

	int pit=img.GetPitch();

	int bitCount=img.GetBPP()/8;

	for (int y = offsets[1]; y < Height - offsets[3]; ++y)
	{
		for (int x = offsets[0]; x < Width - offsets[2]; ++x)
		{
			int pity = pit * y;
			int pitx = x*bitCount;
			if (up[bmp.bmWidth * (bmp.bmHeight - y - 1) + x] != 
(*(pRealData + pity + pitx + 2) << 16) + (*(pRealData + pity + pitx + 1) << 8) + 
*(pRealData + pity + pitx))
			{
				printf("(%d, %d) = %x, ",x, y, up[bmp.bmWidth *
 (bmp.bmHeight - y - 1) + x]);
				printf("(%d, %d) = %x\n",x, y, (*(pRealData + 
pity + pitx + 2) << 16) + (*(pRealData + pity + pitx + 1) << 8) + *(pRealData + 
pity + pitx));
				return false;
			}
		}
	}
	return true;
}

/*
 * hwnd:要截图的窗口的句柄
 * fileName:要比较的图片的路径
 * left:比较图片时的左偏移量
 * top:比较图片时的上偏移量
 * right:比较图片时的右偏移量
 * bottom:比较图片时的下偏移量
 */
int screenPrint(HWND hwnd, const char* fileName, int left, int top, int right, int bottom)
{
	if (left < 0 || top < 0 || right < 0 || bottom < 0)
	{
		return -1;
	}
	int offsets[4];
	offsets[0] = left;
	offsets[1] = top;
	offsets[2] = right;
	offsets[3] = bottom;
	bool isTheSame = print_screen(hwnd, fileName, offsets);
	if (isTheSame)
	{
		return 0;
	}
	else
	{
		return -1;
	}
}

速度尚可，比较两张1024 * 768的图片，耗时200ms以内