c - Copying content from a hidden or clipped window in XP?

Question

I need to copy the content of a window (BitBlt) which is hidden, to another window. The problem is that once I hide the source window, the device context I got isn't painted anymore.

Answer 1

What you need is the PrintWindow function that's available in Win32 API since Windows XP. If you need it to work with older versions of Windows, you can try WM_PRINT, although I've never been able to make it work.

There's a nice article here that shows how to use PrintWindow, and here's the relevant code snippet from that article:

// Takes a snapshot of the window hwnd, stored in the memory device context hdcMem
HDC hdc = GetWindowDC(hwnd);
if (hdc)
{
    HDC hdcMem = CreateCompatibleDC(hdc);
    if (hdcMem)
    {
        RECT rc;
        GetWindowRect(hwnd, &rc);

        HBITMAP hbitmap = CreateCompatibleBitmap(hdc, RECTWIDTH(rc), RECTHEIGHT(rc));
        if (hbitmap)
        {
            SelectObject(hdcMem, hbitmap);

            PrintWindow(hwnd, hdcMem, 0);

            DeleteObject(hbitmap);
        }
        DeleteObject(hdcMem);
    }
    ReleaseDC(hwnd, hdc);
}

I should have some Python code that uses wxPython to achieve the same thing. Drop me a note if you want it.