Freeze the screen

[chris1985]

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

[Salem]

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.

[novacain]

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 ).

[andyhunter]

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:

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