Thread: ScreenShot-10 times in one second and showing it in Image component

  1. #1
    Registered User
    Join Date
    Jan 2010

    ScreenShot-10 times in one second and showing it in Image component

    Hi, I have a big problem. I want to do a program which will get a part of the screen of a program. After that It will show this small rectangle in Image component in BCB. But the problem is, it has to refresh it at least 10 times in one second. For now I succeeded in doing a code that gets a screen but it is too slow. It is refreshing in 2,5-3 seconds(It is copying all pixels separately by GetPixel() function to Image):/ This code below is within a loop. It should show the window but it shows only black screen. When I'm using analogical code but with loading a bitmap from file everthing works fine.


        HDC WinDC;
        HDC CopyDC;
        HBITMAP hBitmap;
        RECT rt;
        HWND Wnd=FindWindow(NULL,"WINDOW");
                  if(Wnd==0) {MessageBox(0,"didnt found the window!",0,0);}
        GetWindowRect (Wnd, &rt);
        WinDC = GetDC (Wnd);
        CopyDC = CreateCompatibleDC (global_hdc);
        std::cout<<rt.right - rt.left<<std::endl;
        std::cout<<rt.bottom -<<std::endl;
        hBitmap = CreateCompatibleBitmap (WinDC,
                                                                    800, //width
        SelectObject (CopyDC, hBitmap);
        BitBlt (global_hdc, //destination
                   800, //width
                   600, //height
                   CopyDC, //source
                   0, 0,
    2.Analogical code with loading from file:

        HBITMAP image;
        BITMAP bm;
        HDC hdcMem;
        //load the bitmap image
        image = (HBITMAP)LoadImage(0,"asteroid.bmp",IMAGE_BITMAP,0,0,LR_LOADFROMFILE);
        //read the bitmap's properties
        GetObject(image, sizeof(BITMAP), &bm);
        //create a device context for the bitmap
        hdcMem = CreateCompatibleDC(global_hdc);
        SelectObject(hdcMem, image);
        //draw the bitmap to the window (bit block transfer)
                   global_hdc, //destination device context
                   0, 0, //x,y location on destination
                   bm.bmWidth, bm.bmHeight, //width,height of source bitmap
                   hdcMem, //source bitmap device context
                   0, 0, //start x,y on source bitmap
                   SRCCOPY); //blit method
        //delete the device context and bitmap

    I want to get a part of window in a game and want to show this rectangle on my form. I've chosen Image component(BCB) for that but I'm not sure that it is enough fast way. I've got known that the problem is that I don't load the bitmap(of the black screen). So I have to load about 10 or more pictures per second from DC of this game window, am I right? But I don't have any idea how to load it from window and put in the image component(I think Image component don't have HDC so I can't use BitBlt function?).

    I would be also grateful for orienting me how to analize pixels as fastly as possible. I mean I want analize about 50000 pixels four times in one second(checking if their color is red).
    Last edited by arva; 01-24-2010 at 08:40 AM.

  2. #2
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    ScreenShot-10 times in one second and showing it in Image component - C++

    You didn't read this sites code posting guidelines.

    Or choose carefully...
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  3. #3
    Registered User
    Join Date
    Jan 2010
    Is this from a Direct3D game?
    From my experience the performance of Direct3D-GDI interactions is very poor. (Personally I find GDI performance in it self to be quite lacking)
    Assuming that you don't have the source code of said game; What I would do is something like
    Hook Direct3D9::Present or EndScene in the game
    Read out the back buffer and write the pixel data to a shared memory mapped file
    Read said pixel data from my external app and render it to a Direct3D surface.

    There are probably easier ways of getting pixel data from a D3D window, but this way you also get the added benefit of being able to control the target's rendering pipeline

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