Freeze the screen

This is a discussion on Freeze the screen within the Windows Programming forums, part of the Platform Specific Boards category; I am using Getpixel() to capture pixels from the screen, but I need to lock the screen to stop it ...

  1. #1
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    Freeze the screen

    I am using Getpixel() to capture pixels from the screen, but I need to lock the screen to stop it from changing before I have had time to scan all the pixels. How do I freeze the screen?

    Thanks

  2. #2
    and the hat of int overfl Salem's Avatar
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    Look for a copy bitmap function in the manual (say) and make a copy of the whole thing in one single call.
    That should keep changes to a minimum.
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  3. #3
    train spotter
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    Look at Device contexts. They contain a bitmap, font, pen ect.

    Try..
    This will not stop the screen changing while your app runs.

    HDC hScreen = GetDC(NULL); // capture current screen

    //extract or copy the bitmap contained in hScreen

    //return hScreen to default items
    ReleaseDC(hScreen); //and free when finished

    I suggest you create a CompatibleBitmap() (in its own CompatibleDC() ) to copy the screen DC ( BitBlt() ).

    Then you can use GetDIBits() ect rather than the slow GetPixel() (all at once / individually ).
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  4. #4
    Handy Andy andyhunter's Avatar
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    You should try using the search function. I answered a very similar question to this not to long ago. Anyway here is some code that locks the screen, then copies the entire contents to memory, finally releases the screen:

    Code:
    HDC hdcScr, hdcMem;
    HWND hwnd;
    HBITMAP hBitmap;
    
        
    If(LockWindowUpdate(hwnd = GetDesktopWindow())) {//locking the screen
    
                   hdcScr = GetDCEx(hwnd, NULL, DCX_CACHE | DCX_LOCKWINDOWUPDATE);
                   hdcMem = CreateCompatibleDC(hdcScr);
                   hBitmap = CreateCompatibleBitmap(hdcScr, 60, 60);
                   SelectObject(hdcMem, hBitmap);
    
                   BitBlt(hdcMem, 0, 0, 60, 60, hdcScr, 0, 0, SRCCOPY);
    
                   //whatever else you want to do
    }
    DeleteDC(hdcMem);
    ReleaseDC(hwnd, hdcScr);
    DeleteObject(hBitmap);
    LockWindowUpdate(NULL); //unlock the screen
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