封存位图代码的一个疑问

保存位图代码的一个疑问

保存位图代码的一个疑问，代码来自：
http://bbs.csdn.net/topics/20173554

代码有个地方没看懂：

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

这句getdibits这个函数的作用是将位图像素 的的数据写到缓冲区域lpbi中的某个位置中！！1


在getdibits之前有这么几句代码：
 lpbi = (LPBITMAPINFOHEADER)GlobalLock(hDib);
    *lpbi = bi;

  很明显是用来设置位图信息头的，

可是我们的调色板结构体，代码却没有呈现，如何写到缓冲区中？

getdibtis这个函数并不是将调色板写到缓冲区中。




int SaveBitmapToFile(HBITMAP hBitmap, LPSTR lpFileName) //hBitmap 为刚才的屏幕位图句柄
 {      //lpFileName 为位图文件名
 HDC     hDC;         
     //设备描述表
 int     iBits;      
   //当前显示分辨率下每个像素所占字节数
 WORD    wBitCount;   
     //位图中每个像素所占字节数
       //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;
 BITMAP          Bitmap;        
 //位图属性结构
BITMAPFILEHEADER   bmfHdr;        
 //位图文件头结构
       BITMAPINFOHEADER   bi;            
 //位图信息头结构 
LPBITMAPINFOHEADER lpbi;          
 //指向位图信息头结构
     HANDLE          fh, hDib, hPal;
 HPALETTE     hOldPal=NULL;
 //定义文件，分配内存句柄，调色板句柄
   
    //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 &lt;= 1)
       wBitCount = 1;
    else if (iBits &lt;= 4)
       wBitCount = 4;
    else if (iBits &lt;= 8)
       wBitCount = 8;
    else if (iBits &lt;= 32)
       wBitCount = 24;
    //计算调色板大小
    if (wBitCount &lt;= 8)
       dwPaletteSize=(1&lt;&lt;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 = GetStockObject(DEFAULT_PALETTE);
    if (hPal)
    {
       hDC = GetDC(NULL);
       hOldPal=SelectPalette(hDC,(HPALETTE)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, (BITMAPINFO *)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;
 }

[解决办法]
The GetDIBits function retrieves the bits of the specified compatible bitmap and copies them into a buffer as a DIB using the specified format.

Syntax
以带有颜色区分的格式查看复制到剪贴板打印int GetDIBits(
__in HDC hdc,
__in HBITMAP hbmp,
__in UINT uStartScan,
__in UINT cScanLines,
__out LPVOID lpvBits,
__inout LPBITMAPINFO lpbi,
__in UINT uUsage
);
int GetDIBits(
__in HDC hdc,
__in HBITMAP hbmp,
__in UINT uStartScan,
__in UINT cScanLines,
__out LPVOID lpvBits,
__inout LPBITMAPINFO lpbi,
__in UINT uUsage
);

Parameters
hdc [in]
A handle to the device context.

hbmp [in]
A handle to the bitmap. This must be a compatible bitmap (DDB).

uStartScan [in]
The first scan line to retrieve.

cScanLines [in]
The number of scan lines to retrieve.

lpvBits [out]
A pointer to a buffer to receive the bitmap data. If this parameter is NULL, the function passes the dimensions and format of the bitmap to the BITMAPINFO structure pointed to by the lpbi parameter.

lpbi [in, out]
A pointer to a BITMAPINFO structure that specifies the desired format for the DIB data.

uUsage [in]
The format of the bmiColors member of the BITMAPINFO structure. It must be one of the following values.

Value Meaning
DIB_PAL_COLORS The color table should consist of an array of 16-bit indexes into the current logical palette.

DIB_RGB_COLORS The color table should consist of literal red, green, blue (RGB) values.

Remarks
If the requested format for the DIB matches its internal format, the RGB values for the bitmap are copied. If the requested format doesn't match the internal format, a color table is synthesized. The following table describes the color table synthesized for each format.

封存位图代码的一个疑问

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