关于位图（Bitmap）

MSDN定义：https://msdn.microsoft.com/en-us/library/dd183377(v=vs.85).aspx

Bitmaps

A bitmap is a graphical object used to create, manipulate (scale, scroll, rotate, and paint), and store images as files on a disk. This overview describes the bitmap classes and bitmap operations.

位图的操作

1. 创建内存DC和位图对象（HBITMAP）

bool startBitMapPage(){HBITMAP hBitmap = NULL;HDC hdcMem = NULL;hdcMem = CreateCompatibleDC(getPrimaryDC());UT_return_val_if_fail(hdcMem, false);hBitmap = CreateCompatibleBitmap(getPrimaryDC(), page_rect.top - page_rect.bottom, page_rect.left - page_rect.right);UT_return_val_if_fail(hBitmap, false);SelectObject(hdcMem, hBitmap);GR_Win32AllocInfo ai(hdcMem, m_pDocInfo, NULL);m_pGraphics = (GR_Win32Graphics *)XAP_App::getApp()->newGraphics(ai);return true;}

这样就讲内存DC和位图对象进行了绑定，接下来可以直接对hdcMem执行各种GDI操作

2. 保存位图对象到文件

转自blog: 

http://blog.csdn.net/desow/article/details/4558776

BOOL SaveBmp(HBITMAP hBitmap, CString FileName)       {       HDC   hDC;       //当前分辨率下每象素所占字节数       int   iBits;       //位图中每象素所占字节数       WORD  wBitCount;       //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=0, dwDIBSize=0, dwWritten=0;         //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, hPal, hOldPal=NULL;               //计算位图文件每个像素所占字节数         hDC   = CreateDC(_T("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 wBitCount = 24;               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.biClrImportant = 0;       bi.biClrUsed = 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);             //hDC   =   m_pDc->GetSafeHdc();           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, (HPALETTE)hOldPal, TRUE);         RealizePalette(hDC);        ::ReleaseDC(NULL, hDC);    }              //   创建位图文件           fh = CreateFile(FileName, 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;    }