EVC实现WIN CE下截屏并且保存到文件[By Erran]

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)
{
    HDC hScrDC, hMemDC;        
    int width, 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 = width;
    RGB24BitsBITMAPINFO.bmiHeader.biHeight = height;
    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, 0, 0, width, height, hScrDC, 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 + ((width*height)*3); ///3=(24 / 8)

//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, 3*width*height, 1, mStream);
//close file
   fclose(mStream);
}

//delete
DeleteObject(hMemDC);
DeleteObject(hScrDC);
DeleteObject(directBmp);
DeleteObject(previousObject);
}