EVC实现WIN CE下截屏并且保存到文件(转载)

在WinCE中, 由于WinCE的精简,有很多win32下的标准API不支持,所以有很多在vc上能够轻易实现的功能, 在evc中有点难度,必须变通一下,就拿截取屏幕来说,一个常用的函数GetDIBits在wince就Unsupported.当时为了实现这个功能, 颇费了了一番心血，当然其主要还是因为对api不是很熟悉。

最初使用的截屏方法说来还真有些丢人，一个一个点的取得颜色值，再保存到bmp文件中去，这样程序运行的速度超慢， 保存一个800X600的bmp差不多要一两分钟（研华8251板），觉得有些不对头，决定想办法改进一下，就使劲地看了一下Charles Petzold先生的《Programming Windows》（这本书很经典，值得好好研究一下），终于把时间缩短到几秒钟了，下面这个函数在evc和vc下都test pass(不用更改)，有不足之处欢迎指正，函数：

// this function create a bmp file to save the current screen;
// supported eVC++ 4.0 (wince 4.0) and vc++ 6.0 , test pass;
void CSnapDlg::OnScreenSave(const char *filename,int startx,int starty,int width,int height)
{ 
    HDC  hScrDC, hMemDC;        
    int iWidth=width,iHeight=height;
 
 //the pointer will save all pixel point's color value
 BYTE  *lpBitmapBits = NULL;
       
 //creates a device context for the screen device
    hScrDC = CreateDC(_T("DISPLAY"), NULL, NULL, NULL);

  //get the screen point size
    width = GetDeviceCaps(hScrDC, HORZRES);
    height = GetDeviceCaps(hScrDC, VERTRES);

    //creates a memory device context (DC) compatible with the screen device(hScrDC) 
    hMemDC = CreateCompatibleDC(hScrDC);

 //initialise the struct BITMAPINFO for the bimap infomation，
 //in order to use the function CreateDIBSection
 // on wince os, each pixel stored by 24 bits(biBitCount=24) 
 //and no compressing(biCompression=0)
    BITMAPINFO RGB24BitsBITMAPINFO;
    ZeroMemory(&RGB24BitsBITMAPINFO, sizeof(BITMAPINFO));
    RGB24BitsBITMAPINFO.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    RGB24BitsBITMAPINFO.bmiHeader.biWidth = iWidth;
    RGB24BitsBITMAPINFO.bmiHeader.biHeight = iHeight;
    RGB24BitsBITMAPINFO.bmiHeader.biPlanes = 1;
    RGB24BitsBITMAPINFO.bmiHeader.biBitCount = 24;
  
  　//use the function CreateDIBSection and SelectObject 
 　//in order to get the bimap pointer : lpBitmapBits
　 HBITMAP directBmp = CreateDIBSection(hMemDC, (BITMAPINFO*)&RGB24BitsBITMAPINFO,
       DIB_RGB_COLORS, (void **)&lpBitmapBits, NULL, 0);
 　HGDIOBJ previousObject = SelectObject(hMemDC, directBmp);

 // copy the screen dc to the memory dc
  BitBlt(hMemDC, startx, starty, iWidth, iHeight, hDC, 0, 0, SRCCOPY);
 
 //if you only want to get the every pixel color value,
 //you can begin here and the following part of this function will be unuseful;
 //the following part is in order to write file;

 //bimap file header in order to write bmp file
 BITMAPFILEHEADER bmBITMAPFILEHEADER;
 ZeroMemory(&bmBITMAPFILEHEADER, sizeof(BITMAPFILEHEADER));
 bmBITMAPFILEHEADER.bfType = 0x4d42;  //bmp 
 bmBITMAPFILEHEADER.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
 bmBITMAPFILEHEADER.bfSize = bmBITMAPFILEHEADER.bfOffBits + ((iWidth*iHeight)*3); ///3=(24 / 8)
 
//Windows 规定一个扫描行所占的字节数必须是4的倍数。
//有可能宽度所占的像素字节数不是4的倍数，所以必须把它转换成4的倍数。
  int DataSizePerLine=((iWidth+3)/4)*4*(iBitCount/8); //ensure the width is the multiple of 4
 int DataSize=DataSizePerLine*iHeight;//实际文件的大小
 //write into file
 FILE *mStream = NULL;
 if((mStream = fopenfilename, "wb")))
 {  
  //write bitmap file header
  fwrite(&bmBITMAPFILEHEADER, sizeof(BITMAPFILEHEADER), 1, mStream);
  //write bitmap info
  fwrite(&(RGB24BitsBITMAPINFO.bmiHeader), sizeof(BITMAPINFOHEADER), 1, mStream);
  //write bitmap pixels data
  fwrite(lpBitmapBits, DataSize, 1, mStream);
   //close file
  fclose(mStream);
 }
 
 //delete
 DeleteObject(hMemDC);
 DeleteObject(hScrDC);
 DeleteObject(directBmp);
 DeleteObject(previousObject);
}