Re: Floating window beside the main app window

From:

Victor <big.boss@chefmail.de>

Newsgroups:

microsoft.public.vc.language

Date:

Fri, 29 Jun 2007 05:41:22 -0700

Message-ID:

<1183120882.243954.13010@q75g2000hsh.googlegroups.com>

Sorry, but I have to raise a new question now.

Well, my floating window does what I need, but there are now some
different problems...

The shown below func gets invoked on the main thread in the
OnInitDialog().

static void CreateScreenWindow(HINSTANCE hInst) {
        const char* className = "ScreenWindow";

        WNDCLASS wc;
        memset(&wc, 0, sizeof(WNDCLASS));

        wc.style = CS_OWNDC;
        wc.lpfnWndProc = (WNDPROC)WndProc;
        wc.hInstance = hInst;
        wc.hCursor = LoadCursor(NULL, IDC_ARROW);
        wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
        wc.lpszClassName = className;

        if (RegisterClass(&wc) == 0) {
                char buf[128];
                sprintf(buf, "Failed to register class (%d)",
GetLastError());
                MessageBox(NULL, buf, NULL, MB_OK);
                return;
        }

        RECT clientSize;
        clientSize.top = 0;
        clientSize.left = 0;
        clientSize.right = 400;
        clientSize.bottom = 250;

        DWORD style = WS_BORDER | WS_CAPTION;

        AdjustWindowRect(&clientSize, style, FALSE);

        int winWidth = clientSize.right - clientSize.left;
        int winHeight = clientSize.bottom - clientSize.top;

        int winLeft = (GetSystemMetrics(SM_CXSCREEN) - winWidth) / 2;
        int winTop = (GetSystemMetrics(SM_CYSCREEN) - winHeight) / 2;

        hScreen = CreateWindow(className, "toolscreen", style,
winLeft,
winTop, winWidth, winHeight, 0, 0, hInst, 0);

        if (hScreen == 0) {
                char buf[128];
                sprintf(buf, "Failed to create window (%d)",
GetLastError());
                MessageBox(NULL, buf, NULL, MB_OK);
                return;
        }

        UpdateWindow(hScreen);
        MoveWindow(hScreen, winLeft, winTop, winWidth, winHeight,
TRUE);
}

The created window does not get shown until a worker thread tells it
to do so somewhen by means of ShowWindow(TRUE). Well, then it
obediently appears on the screen - but the system gets overloaded at
the same moment and stays so till the window disappears through
invoking ShowWindow(FALSE) by the worker thread.
I checked the reason and found that the floating window receives en
masse messages WM_PAINT - several hundreds a second. Gradually
modifying the window proc I made it to contain only the following
code :

case WM_PAINT :
    return 0;

The system stays hopeless overloaded. If altering this code this way:

case WM_PAINT :
    return DefWindowProc(hWnd, msg, wParam, lParam);

the overloading does not take place any more... but the window does
not perform its work any more, too.

My questions now are :

(a) What is the crucial difference between 'return 0' and 'return
DefWindowProc()' in this case that can lead to this drastical
difference in the behaviour?

(b) What - at least theoretically - can cause the flood of WM_PAINT's?

Thanks in advance for everybody who could give me an enlightening
idea.

Victor