Bitblt后图像出现在屏幕右上方而不是窗口中

 void Device::Display()
{
    hdc = GetDC(hwnd);
    BitBlt(hdc, 0, 0, VIEWWIDTH, VIEWHEIGHT, hdcMem, 0, 0, SRCCOPY);
    ReleaseDC(hwnd, hdc);
    for (int j = 0; j < VIEWHEIGHT; j++)
    {
        memset(frameBuffer[j], 0, VIEWWIDTH*sizeof(unsigned int));
    }
}

void Device::Init()
{
    hdc = GetDC(hwnd);
    hdcMem = CreateCompatibleDC(hdc);
    ReleaseDC(hwnd, hdc);//暂时断开
    bmpInfo = { { sizeof(BITMAPINFOHEADER), VIEWWIDTH, -VIEWHEIGHT, 1, 32, BI_RGB, VIEWWIDTH * VIEWHEIGHT * 4, 0, 0, 0, 0 } };
    LPVOID ptr;
    nBmp = CreateDIBSection(hdcMem, &bmpInfo, DIB_RGB_COLORS, &ptr, 0, 0);
    oBmp = (HBITMAP)SelectObject(hdcMem, nBmp);

    frameBuffer = new unsigned int*[VIEWHEIGHT];

    char*framebuf = (char*)ptr;
    for (int j = 0; j < VIEWHEIGHT; j++)
    {
        frameBuffer[j] = (unsigned int*)(framebuf + VIEWWIDTH * 4 * j);
    }
}

hwnd是CreateWindowA返回的窗口句柄。
程序运行结果是这样

参考：http://blog.csdn.net/frenzy/article/details/1432628