紋理貼圖 內存-從內存DC中獲取截取桌的面圖像用於紋理貼圖時，獲取的內容一直是空的怎麼回事

從內存DC中獲取截取桌的面圖像用於紋理貼圖時，獲取的內容一直是空的怎麼回事

我的程序是這樣的，獲取桌面圖像，傳到內存DC，在內存DC中取出圖像，生成紋理（或其他處理操作，比如融合），進行紋理貼圖。
我開始的時候寫了兩個小程序，一個是獲取桌面圖像並顯示，已經成功；一個是從桌面的絕對路徑載入一幅位圖，並用於紋理貼圖，也成功了。
現在想把兩個程序合起來，不用從硬盤讀取的位圖貼圖，改用從DC獲取的位圖貼圖。但是程序運行效果就是貼出的圖灰蒙蒙的白色。經過我自己的實驗，發現如果放位圖的指針地址裡沒有東西的話，就會出現這種效果。
說明我根本沒從內存DC中將位圖取出來，大神們快看看，這個改怎麼解決，已經三天了，實在沒招了。

    glClear(GL_COLOR_BUFFER_BIT| GL_DEPTH_BUFFER_BIT );
    GLfloat ctrlpoints[4][4][3] = {
        {{-2.5,-3, 0.0},{-2,-1.5,0.0},
        {2,-1.5,0.0},{2.5,-3,0.0}},
        {{-3,-1.5,0.0},{-2,-0.3,0.0},
        {2,-0.3,0.0},{3,-1.5,0.0}},
        {{-3.5,0.0,0.0},{-2,0.9,0.0},

        {2,0.9,0.0},{3.5,0.0,0.0}},
        {{-4,1.5,0.0},{-2,2.1,0.0},
        {2,2.1,0.0},{4,1.5,0.0}}
    };
    GLfloat texpts[2][2][2] = {{{0.0, 0.0}, {1.0, 0.0}}, 
    {{0.0, 1.0}, {1.0, 1.0}}};
    glMap2f(GL_MAP2_VERTEX_3,0,1,3,4,0,1,12,4,&ctrlpoints[0][0][0]);
    glMap2f(GL_MAP2_TEXTURE_COORD_2, 0, 1, 2, 2, 
        0, 1, 4, 2, &texpts[0][0][0]);
    glEnable(GL_MAP2_TEXTURE_COORD_2);
    glEnable(GL_MAP2_VERTEX_3);
    glMapGrid2f(20,0.0,1.0,20,0.0,1.0);
    glColor3f (0.0f, 0.0f, 0.0f);  
    //makeImage();
    RECT rcView;
    GetClientRect(&rcView);
    CDC *deskDC = CDC::FromHandle(::GetDC(NULL));//獲取當前DC
    CDC memDC;
    memDC.CreateCompatibleDC(deskDC);//創建兼容DC
    CBitmap pDeskBmp ;
    CBitmap *pOldBmp;
    UINT uDeskBmpWidth = ::GetSystemMetrics(SM_CXSCREEN);//屏幕寬度
    UINT uDeskBmpHeight = ::GetSystemMetrics(SM_CYSCREEN);//屏幕高度
    pDeskBmp.CreateCompatibleBitmap(deskDC, uDeskBmpWidth, uDeskBmpHeight);//創建兼容位圖
    pOldBmp = memDC.SelectObject(&pDeskBmp);//將兼容位圖選入創建的DC中
    memDC.BitBlt(0, 0, uDeskBmpWidth, uDeskBmpHeight, deskDC, 0, 0, SRCCOPY);//將屏幕圖像復制到內存DC中
    BITMAP bmp;
    pDeskBmp.GetBitmap(&bmp);
    bmp.bmBits=(char*)malloc((bmp.bmWidth)*(bmp.bmHeight)*(bmp.bmBitsPixel));

    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    //glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, imageWidth, imageHeight, 0,
    //             GL_BGR_EXT, GL_UNSIGNED_BYTE, data);
    gluBuild2DMipmaps(GL_TEXTURE_2D, GL_RGB, bmp.bmWidth, bmp.bmHeight, 
        GL_BGR_EXT, GL_UNSIGNED_BYTE, bmp.bmBits);//
    glEnable(GL_TEXTURE_2D);
    glEvalMesh2(GL_LINE, 0, 20, 0, 20);
    glFlush();

最佳回答：

問題已經解決，bmp.bmBits=(char*)malloc((bmp.bmWidth)*(bmp.bmHeight)*(bmp.bmBitsPixel));這裡雖然開辟了空間，但是裡面是空的，
////char data = (char)malloc((bmp.bmWidth)*(bmp.bmHeight)*3);
////pOldBmp->GetBitmapBits((bmp.bmWidth)*(bmp.bmHeight)*3, data);
這樣開辟空間就能讀到位圖信息了。